CBSE Class 12

NCERT Solutions for Class 12 Biology Chapter 10 Microbes in Human Welfare

These Solutions are part of NCERT Solutions for Class 12 Biology. Here we have given NCERT Solutions for Class 12 Biology Chapter 10 Microbes in Human Welfare

Question 1.
Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes under a microscope, which sample would you carry and why?
Solution:
Curd. It is simple to carry and easily demonstrate the presence of Lactobacillus bacteria.

Question 2.
Give examples to prove that microbes release gases during metabolism.
Solution:

• Making of dough for bread, dosa, and idli with the help of fermenting microbes. Heat expels the gases and makes the food spongy.
• Production of biogas

Question 3.
In which food would you find lactic acid bacteria? Mention some of their useful applications.
Solution:
Curd. LAB (Lactic Acid Bacteria) produce acids that coagulate and partially digest the milk protein. LAB also play very beneficial role in the stomach to check disease-causing microbes.

Question 4.
Name some traditional Indian foods made of wheat, rice, and Bengal gram (or their products) which involve use of microbes.
Solution:
Idli, Dhokla, Dosa. Several food items such as dosa, idli, jalebi and bread are prepared by fermentation process in which one or more kinds of microbes are used.

Question 5.
In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Solution:
Microbes are very useful to combat disease-causing harmful bacteria. A number of antibiotics have been isolated from microorganisms. An antibiotic is a substance which in low concentration inhibits the growth and metabolic activity of pathogenic organisms without harming the host. Penicillin was the first antibiotic to be discovered by Alexander Fleming from fungus Penicillium notation. Antibiotics are obtained from lichens, fungi, eubacteria, and actinomycetes. Some common antibiotics and their sources are as follows :

1. Polymyxin – Bacillus polymyxa
2. Chloramphenicol – Streptomyces venezuelae
3. Neomycin – Streptomyces fradiae
4. Tetracycline (Terramycin) – Streptomyces rimosus
5. Cephalosporin – Cephalosporium acremonium

Question 6.
Name any two species of fungus, which are used in the production of the antibiotics
Solution:
Penicillium notatum provides antibiotic penicillin and antibiotic fumagillin is obtained from Aspergillus fumigatus.

Question 7.
What is sewage? In which way can sewage be harmful to us?
Solution:
The wastewater containing large amounts of organic matter and microbes is called sewage. The sewage contains many harmful pathogens. It will pollute the natural water bodies like rivers and streams if it is released into them. This will in turn cause the spreading of many communicable diseases which are transmitted through contaminated food and water.

Question 8.
What is the key difference between primary and secondary sewage treatment?
Solution:
Primary (1°) treatment is a physical process that involves for removal of particulate as settleable particles. Secondary (2°) treatment is purely a biological treatment involving microbial oxidation.

Question 9.
Do you think microbes can also be used as a source of energy? If yes, how?
Solution:

Biogas is a mixture of gas containing methane, hydrogen sulphide and carbon dioxide. Methane is the predominant gas. It is produced by microbial activity and is used as a source of energy. The types of gases produced depend upon the types of organic materials they (microbes) use. The bacteria grow anaerobically on cellulose, produce a large amount of meth­ane along with hydrogen and carbon dioxide. These bacteria are collectively called methanogens.

One of the common methanogens is Methanobacterium. Methanogens are commonly found in sewage. They are also found in the rumen (a chamber of the compound stomach) of cattle where a large amount of cellulosic food is present. These bacteria help in the breakdown of cellu­lose and thus play a vital role in digestion (symbiotic digestion). Thus, the excreta (dung) of cattle, commonly called gobar can be used for the produc­tion of biogas and hence called gobar gas.

Question 10.
Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.
Solution:
Due to its hazardous nature and anti-environmental effect the use of chemical fertilisers and chemical insecticides are very illegitimate. The development of biofertilisers and bioinsecticides has enabled us to reduce the use of chemical fertilisers and chemical insecticides. Microbes are very important biological agents as biofertilisers and biopesticides.
Microbes as biofertilisers

1. Free-living nitrogen-fixing bacteria – Azotobactcr, Clostridium.
2. Free-living nitrogen-fixing cyanobacteria – Anabaena, Nostoc.
3. Symbiotic nitrogen-fixing bacteria – Rhizobium
4. Symbiotic nitrogen-fixing cyanobacteria – Azolla – Anabaena
5. Mycorrhiza – symbiotic association between fungi and roots of a higher plant.

Microbes as bio-pesticides:
Biopesticides are that biological agents that are used to control weeds, insects, and pathogens. The microorganisms used as biopesticides are viruses, bacteria, protozoa, fungi, and mites. Some of the biopesticides are being used at a commercial scale. Most important example is the soil bacterium Bacillus thuringiensis (Bt). Spores of this bacterium produce the insecticidal Cry protein. This bacterium was the first biopesticide to be used on a commercial scale in the world. Through the use of genetic engineering, the scientists have introduced the B. thuringiensis toxin gene into plants. Such plants are resistant to attack by insect pests.

Question 11.
Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
Solution:
If the BOD level of A, B and C are 20 mg/L, 8 mg/L and 400 mg/L, the /most polluted one is sample ‘C’ i.e., untreated sewage water. Sample B is the least polluted and it is river water. Sample A is secondary effluent discharged from a treatment plant.

Question 12.
Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol-lowering agents) are obtained.
Solution:
Cyclosporin A – Trichoderma polysporum. Statin – Monascus purpureus.

Question 13.
Find out the role of microbes in the following:

1. Single-cell protein (SCP)
2. Soil

Solution:
1. Single-cell protein (SCP) is the protein extracted from cultivated microbial biomass. Edible mushrooms, yeast cells, and blue-green algae provide high protein resources with some medicinal effects. SCP is available in the forms of fresh cells, dry cells, tablets, or extracts.

2. The use of biological methods for controlling plant diseases and pests is called biocontrol. This method has been replaced by the indiscriminate use of chemicals used in the chemical control of pests. The chemicals used for killing pests are toxic and extremely harmful to men and domestic animals. They also pollute the environment and our crop plants.

Question 14.
Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, citric acid, penicillin and curd
Solution:
The correct order from viewpoint of human welfare should be as follows: Penicillin > biogas > citric acid > curd Penicillin is an antibiotic, which is used to combat pathogenic microorganisms. Today, we cannot imagine a world without antibiotics because antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu) and leprosy (kusht rog), which used to kill millions of people all over the globe. It should be given first priority.

As we are going to face a great crisis of fossil fuels in near future, biogas can be the legitimate and brilliant alternative to fossil fuels. It can be used as fuel for heating, cooking, lighting, power for irrigation and other purposes. It is considered an eco-friendly and pollution-free energy source.
Citric acid is produced through the fermentation carried out by Aspergillus niger on many carbohydrates. Citric acid is used in medicines, dyeing, mirror silvering, manufacture of ink, flavouring and preservation of food and candies.

Curd is prepared by fermentation of milk. Fermentation agents are lactic acid bacteria. Curd is more nutritious than milk as it contains a number of vitamins and organic acids.

Question 15.
How do biofertilisers enrich the fertility of the soil?
Solution:
The use of biological methods for controlling plant diseases and pests is called biocontrol. This method has been replaced by the indiscriminate use of chemicals used in the chemical control of pests. The chemicals used for killing pests are toxic and extremely harmful to men and domestic animals. They also pollute the environment and our crop plants.

We hope the NCERT Solutions for Class 12 Biology Chapter 10 Microbes in Human Welfare help you. If you have any query regarding NCERT Solutions for Class 12 Biology Chapter 10 Microbes in Human Welfare, drop a comment below and we will get back to you at the earliest.

Here we are providing NCERT Solutions for Class 12 English Vistas Chapter 2 The Tiger King. Students can get Class 12 English The Tiger King NCERT Solutions, Questions and Answers designed by subject expert teachers.

The Tiger King NCERT Solutions for Class 12 English Vistas Chapter 2

The Tiger King NCERT Text Book Questions and Answers

The Tiger King Reading with insight

Question 1.
The story is a satire on the conceit of those in power. How does the author employ the literary device of dramatic irony in the story?
Answer:
The story is a poignant satire on the abuse of power by the people in powerful positions. The Maharaja, fearing the prophecy that he would meet his death from the hundredth tiger, launched a feverish hunt in the name of “self-defence”.The state banned tiger hunting by anyone except the Maharaja. He declared that the property of the person, who dared to hunt a tiger, would be confiscated. The king was all set to realise his ambition. He vowed to attend to other matters only after killing of a hundred tigers. In the process, he came close to losing his throne when he refused permission to a high-ranking British officer to hunt tigers in his state.

When there were no more tigers left in his kingdom, he married a girl of a state with a large tiger population. With the passage of time, tigers had become extinct even in his father-in-law’s kingdom. On hearing the news of a tiger in a village of his kingdom, the Maharaja whimsically announced a three- year exemption from all taxes for that village and set out on the hunt at once.

When the tiger was not found, many officers lost their jobs. He put his whole kingdom through misery, threatening to take away jobs and double the taxes, until he was presented with the hundredth tiger. Ironically, in spite of his frenzied initiative to negate the prophecy, he met with his death at the hands of a wooden, toy tiger. In this way, the hundredth ‘toy tiger’ took its final revenge upon the Tiger King.

Dramatic irony is employed in the ironical twist in the tale— ninety-nine tigers were killed in vain, and the king came under threat from a wooden toy tiger. There is also a great deal of irony in how contrary to the ferociousness of tigers, the hundredth tiger was old and fainted from the shock of the bullet whizzing past. The tale is a satire on the pompous Maharaja, who heartlessly killed a hundred tigers, only to meet his nemesis in a toy.

Question 2.
What is the author’s indirect comment on subjecting innocent animals to the wilfulness of human beings?
Answer:
Through the story “The Tiger King”, the writer puts across his view of condemning the killing of animals. The Maharaja, the protagonist of the story, scared of a prophecy, killed tigers mercilessly. The author also raises a contemporary concern of the present times—the extinction of wildlife due to human activities. Asserting the “right” to kill animals is like asserting the right to steal, from future generations. The tiger population became extinct in the territories where he had an access to kill. The writer garbs it in the guise of a folklore, but addresses how merciless killing of animals leads to a depletion of natural resources. The sensitive environmental issue of certain species becoming extinct is beautifully and humorously conveyed.

Question 3.
How would you describe the behaviour of the Maharaja’s minions towards him? Do you find them sincere towards him or are they driven by fear when they obey him? Do we find a similarity in today’s political order?
Answer:
Since the Maharaja’s existence revolved around killing a hundred tigers, his minions, driven by fear, obeyed him. Even the astrologer was afraid of predicting his death till the Maharaja told him to “speak without fear”. Determined to fulfil his mission, the Maharaja threatened to confiscate the wealth and property of any person who dared to hurt a tiger.

Overtaken by the madness to kill hundred tigers, he unjustly levied taxes and threatened his subjects to take away their jobs. The minions seemed afraid of their whimsical monarch. They kept their opinions to themselves, and watched as their king drove the entire nation to risk for his personal agenda. In today’s political order, we have such examples of autocratic rulers and dynastic monopolies throughout the world. In many countries we see that the role of money, crime, electoral manipulation and muscle power greatly influences political decisions. Sycophants prevent those in power from seeing the truth.

Question 4.
Can you relate instances of game hunting among the rich and the powerful in the present times that illustrate the callousness of human beings towards wildlife?
Answer:
While not every medieval noble ever went off to war, they all, if physically able, went off to hunt on horseback. Hunting was the favourite pastime of the warrior class.However, in the recent past, when poaching has been made illegal, most hunters get away with murder in India. When Mansur Ali Khan Pataudi was apprehended for hunting down an endangered species of black buck, the ruthless, arrogant lifestyle of some Indians with inherited fortunes were exposed.

For years, animals—especially tigers and elephants—have been killed for their skins and organs. National parks, sanctuaries, and reserves have been virtually turned into hunting grounds by poachers. Armed with sophisticated weapons and vehicles, supported by corrupt officials and politicians, and glamorised by movie stars like Salman Khan, who was arrested for killing the black buck in Rajasthan, the poachers have ruled the jungles with little fear.

All this has led to certain species becoming extinct due to encroachment and hunting by human beings. One such example is the Tibetan Antelope, which has been hunted down by poachers for its skin, used to make the Shahtoosh shawl. This antelope yields one of the finest and most expensive wools in the world—a prized possession of the rich. Pearl essence is obtained primarily from herring and is one of the many by-products of large-scale commercial fishing.

Question 5.
We need a new system of the age of ecology—a system that will take care of all people and of the earth and of all life upon it. Discuss.
Answer:
In our diverse and increasingly interdependent world, it is crucial that we, the people of earth, declare our responsibility to the greater community of life. The survival of our earth depends upon the consciousness that we should move beyond nationalism to more global concerns, for instance, to a sense of bio-regionalism. The well-being of people and the biosphere depends upon preserving clean air, pure waters, fertile soils, and a rich variety of plants, animals and ecosystems. The global environment with its finite resources is a primary concern of all humanity. The community of our planet stands at a defining moment. With science and technology have come great benefits and also great harm.

The dominant patterns of production and consumption are altering the climate, degrading the environment, depleting resources, and causing massive extinction of species. A dramatic rise in population has increased the pressures on ecological systems and has overburdened social systems. The challenges humanity faces can only be met if people everywhere acquire an awareness of global inter- dependence, identify themselves with the larger world, and decide to live with a sense of universal responsibility.

The Tiger King Extra Questions and Answers

The Tiger King Short Answer Questions

Question 1.
Who was the Tiger King? Why was he so named?
Answer:
When the king was bom, the astrologers had foretold that one day he would be killed by a tiger. The king, they predicted, would grow up to become the greatest of all warriors, heroes and champions, but since he was bom in the hour of the bull, predicted that he would meet his end at the hand of its nemesis—the tiger.

Question 2.
When did the king kill his first tiger? What was his reaction?
Answer:
When the Maharaja came of age at twenty, he became the ruler of the State. It was then that he heard of the astrologer’s prediction. He immediately launched on a spree to kill hundred tigers, and killed the first of them around that time. He justified his hunt by calling it an act of “self-defence”. He was thrilled with his first kill, but was soon unsettled when the astrologer predicted that it would be the hundredth tiger that would kill him.

Question 3.
“The king seemed well set to realise his ambition.” What was his ambition? How did he set out realising it?
Answer:
The king’s ambition was to kill a hundred tigers. He went forth fearlessly, there were times when the bullet missed its mark, the tiger leapt upon him and he fought the beast with his bare hands. Each time it was the Maharaja who won.

Question 4.
The tiger hunt almost cost the Maharaja his throne. How?
Answer:
A high-ranking British officer visited Pratibandapuram. He was very fond of hunting tigers. He was keener on being photographed with the tigers he had shot. He wished to hunt tigers in Pratibandapuram. But the Maharaja firmly refused permission. He even refused to let him be photographed, standing over the tiger’s carcass. But the Maharaja appeased the officer by sending his wife expensive diamond rings as gifts.

Question 5.
What difficulty awaited the Maharaja’s tiger hunts after he killed seventy of them? How did he solve the situation?
Answer:
Within ten years of his hunt for tigers, the Maharaja succeeded in killing seventy tigers. With that, the tigers became extinct in the forests of Pratibandapuram. To resolve the issue, the Maharaja decided to get married to a girl of a royal family of the state with the highest tiger population.

Question 6.
What incentive did the Maharaja give to the village with the hundredth tiger? What was his reaction when the tiger was not found?
Answer:
The Maharaja announced a three-year exemption from all taxes for the village where a tiger was spotted. When the tiger was not found, the Maharaja refused to leave the forest until the tiger was found. As the days passed, many officers lost their jobs, he doubled the land tax, and threatened the.dewan, asking him to resign.

Question 7.
How was the hundredth tiger found?
Answer:
The dewan got a tiger from the People’s Park in Madras and kept it hidden in his house. At midnight when the town slept in peace, the dewan and his aged wife dragged the tiger to the car and shoved it into the seat. The dewan himself drove the car straight to the forest where the Maharaja was hunting.

Question 8.
Bring out the irony in the end of the story.
Answer:
The Maharaja, the greatest of warriors and heroes, was killed by a wooden tiger that cost only two annas and a quarter. After he spent years hunting down tigers to avoid the death that was predicted, he met his end at the hands of a toy tiger. The irony lay in the strange way his fate unfolded.

The Tiger King Long Answer Question

Question 1.
Bring out the irony in the title “The Tiger King”.
Answer:
The Maharaja of Pratibandapuram took on the title of His Highness Jamedar-General, Khiledar-Major, Sata Vyaghra Samhari, Maharajadhiraja Visva Bhuvana Samrat, Sir Jilani Jung Jung Bahadur; but this name was often shortened to Tiger King. As his name suggested, the astrologers predicted that he would grow up to become the warrior of warriors, hero of heroes, and champion of champions. They also foretold that he would be killed by a tiger.

However, his death was an anti-climax. He had killed ninety-nine tigers to overwrite the prediction of the astrologer. However, he died — not a valiant death on the battlefield or while hunting a tiger. Instead, his death was caused by a wooden tiger that cost only two annas and a quarter. The surface of the tiny little • wooden tiger, carved by an unskilled carpenter, was rough and had tiny slivers of wood like quills all over it. One of those quills pierced the Maharaja’s right hand. The next day, infection flared in the Maharaja’s right hand. In four days, it developed into a suppurating sore which spread all over the arm. Three famous surgeons operated but could not save him.

Question 2.
“The Tiger King” was punished for his crime of killing the tigers. Comment.
Answer:
The day the Maharaja was bom, astrologers predicted that he would be killed by a tiger as he was bom in the hour of the bull, which had a tiger for its enemy. The hundredth tiger would be the cause of his death. As the Maharaja grew up, he set out to hunt all the tigers, vowing he would attend to all other matters only after killing a hundred tigers. He was well set to realize his ambition. There was a time when the bullet missed its mark, the tiger leapt upon him, and he fought the beast with his bare hands.

Each time, it was the Maharaja who won. Within ten years, the tiger population became extinct in the forests of Pratibandapuram. To kill thirty more tigers, he married a girl from the royal family of a state with a large tiger population. After his marriage, Maharaja Jung Jung Bahadur killed five or six tigers each time he visited his father-in-law. In this manner, the number rose to ninety-nine. But, as luck would have it, he missed killing the hundredth tiger as it was still alive when the Maharaja took him for dead.

The Maharaja, however, paid for his deeds. His death was caused by a wooden tiger that cost only two annas and a quarter. The tiny little wooden tiger that he got as a gift for his son had been carved by an unskilled carpenter. Its surface was rough and tiny slivers of wood stood up like quills all over it. One of those slivers pierced the Maharaja’s right hand. The next day, infection flared in the Maharaja’s right hand. In four days, it developed into a suppurating sore which spread all over the arm. Despite famous surgeons operating on it, he could not be saved.

Question 3.
Why does the writer say: “Even the threat of a Stuka bomber will not throw me off track.”
Answer:
The Junkers Ju 87 ‘Stuka’ was a plane used by the Germans as a dive bomber. It was instantly recognizable with its inverted gull-wings and fixed undercarriage. The bomber’s accuracy was high when in a full dive as it used an automatic pull-up system to ensure that the plane pulled out of the dive once the bomb was released. The wheel covers were fitted with sirens that were used once the planes went into a dive, to shatter the morale of enemy troops and civilians. The fins of the bombs were also fitted with whistles to ensure that those being bombed knew just when the bombs were released and could track them on the way down. This was supposed to generate fear in them. The writer refers to the Stuka bombers to convey that nothing, not . even a horrific thing like a Stuka Bomber, could deter him from telling the story.

Question 4.
What does the writer mean when he says: “As Bharata said to Rama about Dasaratha, the Tiger King has reached that final abode of all living creatures”?
Answer:
In the Ramayana, Kaikeyi, the last and youngest of Dasaratha’s three wives, on Manthara’s advice, forced Dasaratha to banish Rama from the kingdom for a period of no less than fourteen years and place her son, Bharata, upon the throne of Ayodhya. Honouring his father’s vow, Rama relinquished his claim to the throne and left. In time, Dasaratha lost the will to live and died of grief.

Outraged at his mother’s act and grieved at the loss of his father, Bharata went to get back his brother Rama to take over as the next king. As Bharata conveyed to Rama the news about Dasaratha’s demise, the writer conveyed the news of Tiger King’s death to the reader in a similar fashion.

Question 5.
Explain the miracle that happened soon after the Maharaja was born.
Answer:
When the Maharaja was only a ten-day-old infant, a miracle occurred. The astrologers predicted that one day the king would grow up to become a valiant warrior. He would be one of the greatest heroes but would one day have to meet his death. As the astrologers foretold his future, a great miracle took place. The ten- day-old Maharaja spoke.

He said that all mortals would one day have to die. He wanted to know the cause of his death. The chief astrologer was wonderstruck. The infant Maharaja had not only spoken, but had also raised an intelligent question. The chief astrologer predicted that the prince was bom in the hour of the bull. The bull and the tiger being enemies; the Maharaja’s death would come from the tiger. As soon as Jung Jung Bahadur heard of the prophecy, he shouted a warning to all the tigers—“Let tigers beware!”

Question 6.
How did the Maharaja come close to losing his throne? How did he save it?
Answer:
Maharaja Jung Jung Bahadur had issued an order forbidding anyone but himself from shooting tigers in his kingdom. This order put him in danger of losing his throne. Once, a high-ranking British officer who was very fond of hunting tigers visited Pratibandapuram. He wished to hunt tigers in Pratibandapuram, but the Maharaja declined. The Maharaja not only sent a message forbidding him to kill tigers but he also refused to let the officer be photographed holding the gun and standing over the tiger’s carcass.

Since he prevented a British officer from fulfilling his desire, he stood in danger of losing his kingdom. Hence, the Maharaja sent a telegram to a famous company of jewellers in Calcutta to send samples of expensive diamond rings of different designs. About fifty rings were sent. The Maharaja sent the whole lot to the British officer’s wife expecting her to choose one or two rings and send the rest back. But she kept all of them for herself. The Maharaja had to foot a bill for three lakh rupees but was happy that he had managed to retain his kingdom.

Question 7.
In Pratibandapuram it was “easier to find tiger’s milk than a live tiger”. Why was this so?
Answer:
After the Maharaja had heard of the astrologer’s prediction, he set out to hunt a hundred tigers. He vowed he would attend to all other matters only after killing a hundred tigers. Within ten years, he was able to kill seventy tigers, but with this the tiger population became extinct in the forests of Pratibandapuram. To kill thirty more tigers, he asked his minister to find a girl from a royal family in a state with a large tiger population.

After the right girl was found, the Maharaja Jung Jung Bahadur killed five or six tigers each time he visited his father- in-law. In this manner, the number rose to ninety-nine. But, when just one tiger was left to achieve his count of a hundred, and he could not find another tiger, he sank into gloom. Finding a tiger was next to impossible. Here the author has used a hyperbole to stress the scarcity of tigers for a comical effect. Tiger’s milk, which is impossible to find, is used to convey that it became next to impossible to find a live tiger in Pratibandapuram.

Question 8.
Did the Maharaja ‘kill’ the hundredth tiger? Why/why not?
Answer:
After the Tiger King had killed ninety-nine tigers, the Maharaja sank into gloom as he could not find the hundredth tiger. Then, one day, when he heard that in his own state the sheep had begun to disappear from a hillside village, his hopes began to rise. Delighted, he even announced a three-year exemption from all taxes for the village and set out to find the tiger. But it was in vain. Furious, the Maharaja threw out many officers and doubled the land tax there.

The worried dewan was relieved when a tiger was brought from the People’s Park in Madras and he kept . it hidden in his house. At midnight, the dewan and his wife dragged the tiger to the car and drove it till the forest where the Maharaja was hunting. With a great difficulty, the dewan pushed it out. The next day, the old tiger wandered into the Maharaja’s presence. The Maharaja shot the beast and the tiger fell to the ground. The overjoyed Maharaja left after ordering that the tiger be brought to the capital in a grand procession, After
the Maharaja left, the hunters realized that the tiger was not dead; it had merely fainted from the shock of the bullet that went past it. For the fear of losing their jobs, the hunters decided to keep away the truth from the Maharaja and shot the tiger dead.

Question 9.
Why did the hunters not tell the Maharaja that he had failed in his mission of killing the hundredth tiger?
Answer:
After a great deal of effort, the Maharaja found the hundredth tiger. Ironically, for the Maharaja, who had earlier fought and killed a tiger bare-handed, killing the old tiger would have been a cake-walk; and yet destiny did not allow this. The Maharaja shot the tiger and thinking it dead, left the forest, feeling elated. But when the hunters took a closer look at the tiger, it rolled its eyes in bewilderment. The men realized that the tiger was not dead. The Maharaja’s bullet had missed it.

Nevertheless, it had fainted from the shock of the bullet speeding past. The hunters decided that the Maharaja must not come to know that he had missed his target. He was quick to anger and would punish them. They would lose their jobs or worse. Hence, one of the hunters took aim from a distance of one foot and shot the tiger. This time, the tiger was killed. But the Maharaja was blissful in his ignorance.

Question 10.
The story is a satire on the conceit of those in power. Comment.
Answer:
The story, “The Tiger King”, is a poignant satire on the self-importance that the people in power assume. Because of a prophecy made at the time of his birth, the Maharaja shouted a warning to all the tigers—’’Let tigers beware!” After he grew older, he started his tiger hunt in the innumerable forests in Pratibandapuram State and justified the act as he was doing so in “self-defence”. He banned tiger hunting in the State by anyone other than him and declared that the property of the person who would hurt a tiger would be confiscated. He vowed to attend to all other matters only after killing hundred tigers. After killing all the seventy tigers in his own kingdom, the Maharaja married a girl of a state with a large tiger population.

Soon, tigers became extinct even in his father-in-law’s kingdom. Hearing the news of a tiger in a village announced a three-year exemption from all taxes for that village and set out on the hunt at once. After shooting the tiger the Maharaja was relieved. However, the warrior of warriors, hero of heroes, and champion of champions did not die a valiant death on the battlefield or while hunting a tiger. Instead, his death was caused by infection resulting from a wound caused by a wooden tiger that cost only two annas and a quarter.

Question 11.
Human beings view nature merely as a resource to be exploited or even an enemy that needs to be vanquished. Comment with reference to The Tiger King.
Answer:
The author in the story “The Tiger King” expresses the view that there is no excuse or justification for stalking and killing an animal. Because of his blind faith in prophecy, the Maharaja kills tigers aimlessly. Ironically, he who had confessed as a child that “all those who are bom will one day have to die”, later sets out to become immortal by killing tigers, indiscriminately. Hunting animals by humans operates perversely. The Maharaja’s only need was to prove his masculinity, his dominance by killing hapless animals.

The writer reaffirms a very valid reason against hunting—the extinction of species due to human activities. We realize that asserting the right to kill animals is like asserting the right to steal from future generations. The Maharaja steals tigers from the future. The tiger population became extinct in the territories where he had an access to kill. Thus, the next generation would not have the right to see and learn from the bountiful earth that they inherited because the present generation would have left it barren.

NCERT Solutions for Class 12 Physics Chapter 14 Electronics Devices

NCERT Solutions for Class 12 Physics Chapter 14 Electronics Devices are part of NCERT Solutions for Class 12 Physics. Here we have given. NCERT Solutions for Class 12 Physics Chapter 14 Electronics Devices

Question 1.
In an n-type silicon, which of the following statement is true :
(a) Electrons are majority carriers and trivalent atoms are the dopants.
(b) Electrons are minority carriers and pentavalent atoms are the dopants.
(c) Holes are minority carriers and pentavalent atoms are the doplants.
(d) Holes are majority carriers and trivalent atoms are the dopants.
Answer:
(c) ‘Holes are minority carriers and pentavalent atoms are the dopants in n type semiconductor.’

Question 2.
Which of the statements given in Exercise 1 is true for p-type semiconductors ?
Answer:
(d) Holes are majority carriers and trivalent atoms are the dopants in p-type semiconductors.

Question 3.
Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to (Eg)c, (Eg)si and (Eg)Ge-
Which of the following statements is true ?
(a) (Eg)Si < (Eg)Ge < (Eg)c
(b)(E)c<(Eg)Ge>(Eg)si
(c) (Eg)c > (Eg)si > (Eg)Ge
(d) (Eg)c = (Eg)si = (Eg)Ge
Answer:
(C) (Eg)c > (Eg)Si > (Eg)Ge. Energy band gap is maximum in carbon and least in germanium among the given elements.

Question 4.
In an unbiased p-n junction, holes diffuse from the p-region to n-region because
(a) free electrons in the n-region attract them.
(b) they move across the junction by the potential difference.
(c) hole concentration in p-region is more as compared to n-region.
(d) All the above.
Answer:
(c) hole concentration in p-region is more as compared to n-region because hole diffusion takes place from higher concentration to lower concentration.

Question 5.
When a forward bias is applied to a p-n junction, it
(a) raises the potential barrier
(b) reduces the majority carrier current to zero
(c) lowers the potential barrier
(d) none of the above.
Answer:
(c) lowers the potential barrier by cancelling the depletion layer.

Question 6.
For transistor action, which of the following statements are correct :
(a) Base, emitter and collector regions should have similar size and doping concentrations.
(b) The base region must be very thin and lightly doped.
(c) The emitter junction is forward biased and collector junction is reverse biased.
(d) Both the emitter junction as well as the collector junction are forward biased.
Answer:
(b) and (c) : The base region must be very thin, lightly doped and the emitter junction is forward biased whereas collector junction is reverse biased to avoid unnecessary diffusion of charge carrier in the base and also for proper amplification.

Question 7.
For a transistor amplifier, the voltage gain :
(a) remains constant for all frequencies.
(b) is high at high and low frequencies and constant in the middle frequency range.
(c) is low at high and low frequencies and constant at mid frequencies.
(d) None of the above.
Answer:
(c) is low at high and low frequencies and constant at mid frequencies as per frequency response of a transistor.

Question 8.
In half-wave rectification, what is the output frequency if the input frequency is 50 Hz. What is the output frequency of a full-wave rectifier for the same input frequency.
Answer:
A half wave rectifier rectifies only one half cycle of input A.C.
.’. frequency of the output A.C.
= frequency of input A.C. = 50 Hz A full wave rectifier rectifies both halve cycles
of the A.C. input
.’. frequency of output A.C. = 2 x frequency of input A.C. = 2 x 50 = 100 Hz

Question 9.
For a CE-transistor amplifier, the audio signal voltage across the collector resistance of 2 kQ is 2 V. Suppose the current amplification factor of the transistor is 100, find the input signal voltage and base current, if the base resistance is 1 kΩ.
Answer:


Question 10.
Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 volt, calculate the output ac signal.
Answer:


Question 11.
A p-n photodiode is fabricated from a semiconductor with bandgap of 2.8 eV. Can it detect a wavelength of 6000 nm ?
Answer:

Since the energy of the light photon is less than the bandgap energy of the p-n diode, it can not be detected.

Question 12.
The number of silicon atoms per m³ is 5 x 10²⁸. This is doped simultaneously with 5 x 10²² atoms per m³ of Arsenic and 5 x 10²⁰ per m³ atoms of Indium. Calculate the number of electrons and holes. Given that n_i = 1.5 x 10¹⁶ m^-3. Is the material n-type or p- type ?
Answer:


Question 13.
In an intrinsic semiconductor, the energy gap E_g is 1.2 eV. Its hole mobility is much smaller than electron mobility and independent of temperature. What are the ratio between conductivity at 600 K and that at 300 K? Assume that the temperature dependence of intrinsic carrier concentration n_i is given by

Answer:

Thus, conductivity of a semiconductor increases with rise in temperature.

Question 14.
In a P-n junction diode, the current I can be expressed as

where I₀ is reverse saturation current. V is the voltage across the diode and is positive for forwarding bias and negative for reverse bias, and I is the current through the diode, K_B is the Boltzmann constant (8.6 x 10^-5 eV/K) and T is the absolute temperature. If for a given diode I₀ = 5 x 10^-12 A and T = 300 K, then
(a) What will be the forward current at a forwarding voltage of 0.6 V?
(b) What will be the increase in the current if the voltage across the diode is increased to 0.7 V?
(c) What is the dynamic resistance?
(d) What will be the current if reverse bias voltage changes from 1 V to 2 V?
Answer:
The statement of the given question is incorrect. The relation should be

Question 15.
You are given the two circuits as shown in Figure. Show that circuit (a) acts as OR gate while circuit (b) acts as AND gate.

Answer:


Question 16.
Write the truth table for a NAND gate connected as given in Fig. Hence identify the exact logic operation carried out by these circuits.

Answer:
The NAND gate shown in the truth table has only one input. Therefore, the truth table is

Since Y = \( \bar { A }\) in this case, the circuit is actually a NOT gate with the truth table

Question 17.
You are given two circuits as shown in Fig., which consist of NAND gates. Identify the logic operation carried out by the two circuits.

Answer:

Question 18.
Write the truth table for circuit given in Fig. below consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing.

Answer:
Let y₁ be the output which appears at the first operation of NOR gate.

Question 19.
Write the truth table for the circuits given in Fig., consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits

Answer:

We hope the NCERT Solutions for Class 12 Physics Chapter 14 Electronics Devices, help you. If you have any query regarding NCERT Solutions for Class 12 Physics Chapter 14 Electronics Devices, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 12 Biology Chapter 9 Strategies for Enhancement in Food Production

These Solutions are part of NCERT Solutions for Class 12 Biology. Here we have given NCERT Solutions for Class 12 Biology Chapter 9 Strategies for Enhancement in Food Production

Question 1.
Explain in brief the role of animal husbandry in human welfare.
Solution:

• Animal husbandry evolves new techniques and technologies for the management of livestock like buffaloes, cows, pigs, horses, cattle, sheep, camels, goats, etc., that are useful to humans.
• These methods can also be applied to rearing animals like bees, silkworms, prawns, crabs, fishes birds, pigs, cattle, sheep, and camels for their products like milk, eggs, meat, wool, silk, honey, etc.

Role of animal husbandry in human welfare is discussed as follows:

1. Milk is an important product of farm animals that are consumed as such, in the form of curd, cheese, butter, ice cream, etc. Milk is the only source of animal protein for vegetarians and is a complete food. Most of the milk is obtained from cows and buffalo. Other milk-yielding animals are goat, sheep, camel, and yak.
2. Egg, like milk, is also a complete food. Chicken and duck are the two major sources of the egg.
3. Meat is a protein-rich diet that is obtained from all types of livestock, e.g., goat, sheep, pig, cattle, chicken, fish, etc.
4. Honey is a sweet syrup obtained from the hives of the honey bee. Honey is used in sweetening various preparations.
5. Fibers like wool and silk are two high-quality fibres which we get from animals. Wool is the hair of sheep, some goats, and rabbits. Silk is a product of silkworms.
6. The skins of many animals are converted into hides and leather.
7. Drought animals are trained to carry men and materials besides other functions, e.g., buffalo, bullock, horse, camel, ass, elephant, reindeer, yak.
8. The rearing of animals provides employment to many persons.
9. Animal byproducts like horns, feathers, bone, dung, and droppings are all used in developing useful products.

Question 2.
If your family owned a dairy farm, what measures would you undertake to improve the quality and quantity of milk production?
Solution:
Some of the measures to be followed for proper management of dairy farm are :

1. Selection of good breeds having high milk yielding potential according to the climatic conditions of the area.
2. The shed under which the cattle are kept should be well ventilated with an adequate water supply for drinking as well as for washing. Shed should have pucca floor and proper drainage channel.
3. The feed of the animals should be a balanced diet with right proportions of carbohydrates, fats, proteins, and roughage and it should be given timely in good quantity.
4. Cleanliness and hygiene comes first for maintaining the livestock’s health and productivity. So, washing cattle and taking precautionary measures while milking are a must.
5. Inspection, keeping records of the activities and consulting a veterinary doctor for regular checkups of the livestock should be undertaken.

Question 3.
What is meant by the term ‘breed’? What are the objectives of animal breeding?
Solution:
A group of animals which are related by descent to each other and possess similar characteristics like appearance, size, features etc. are said to belong to a breed. The purpose of animal breeding is to produce animals with increased yield, faster growth, improved reproductive rate.

Question 4.
Name the methods employed in animal breeding. According to you which of the methods is best? Why?
Solution:
Animal breeding is producing improved breeds of domesticated animals by improving their genotypes through selective mating. There are two methods of animal breeding, natural breeding which includes inbreeding, out-breeding, cross-breeding, out-crossing, etc., and artificial breeding which involves artificial insemination and multiple ovulation embryo transfer technology (MOET). It involves inseminating the native cows with the semen of superior bulls of exotic or indigenous breeds. Artificial breeding is the best method of breeding because of the following reasons:

• Semen collected from males may be used immediately or can be frozen and used later.
• The semen of desired bulls is collected under hygienic conditions, preserved, and sent to all insemination centres throughout the country.
• Semen collected from one bull can be used to inseminate many cows as fewer sperms are required to achieve conception when semen is deposited artificially. Hence, artificial insemination is very economical.
• It is healthier as the spread of sexually transmitted diseases can be controlled by this technique.

Question 5.
What is apiculture? How is it important in our lives?
Solution:
Apiculture is the practice of bee-keeping for the production of various products such as honey-bee’s wax, etc. Honey is a highly nutritious food source and is used as an indigenous system of medicines. Other commercial products obtained from honeybees include bee’s wax and bee pollen. Bee’s wax is used for making cosmetics, polishes and is even used in several medicinal preparations. Therefore, to meet the increasing demand of honey, people have started practicing bee-keeping on a large scale. It has become an income-generating activity for farmers since it requires low investment and is labour intensive.

Question 6.
Discuss the role of fishery in the enhancement of food production.
Solution:
Fishery is the rearing, breeding, catching & marketing of fishes and other aquatic animals. Fishes are important food for a large portion of human population. Meat of fishes is a rich source of proteins and other useful substances like polyunsaturated fatty acids (PUFA). The meat of other aquatic animals like prawn, crab is also consumed as food by human beings.

Question 7.
Briefly describe various steps involved in plant breeding.
Solution:
The major steps in breeding a new genetic variety of a crop are as follows:

1. Collection of variability.
2. Evaluation and selection of parents.
3. Cross-hybridization among the selected parents.
4. Selection and testing of superior recombinants.
5. Testing, release, and commercialization of new cultivars.

Question 8.
Explain what is meant by biofortification.
Solution:
Biofortification is method of breeding crops with higher levels of vitamins and minerals, or higher proteins and healthier fats in view to improve public health. E.g., iron-fortified rice containing five times more iron than other varieties, wheat variety, Atlas 66 having high protein content, maize varieties having high lysine and tryptophan are produced.

Question 9.
Which part of the plant is best suited for making virus-free plants and why?
Solution:
The terminal bud having apical meristem are the best-suited parts of the plant for making a virus-free plant because they are not infected by a virus.

Question 10.
What is the major advantage of producing plants by micropropagation?
Solution:
Micropropagation is the tissue culture technique used for rapid vegetative multiplication of ornamental plants and fruit trees by using small-sized explants. Because of the minute size of the propagules in the culture, the propagation technique is named micropropagation. This method of tissue culture produces several plants. Each of these plants will be genetically identical to the original plant from which explants were taken. Plants obtained by vegetative propagation of a single plant constitute a somaclonal. The members of a single somaclonal have the same genotype. It is the only process adopted by Indian plant biotechnologists in different industries mainly for the commercial production of ornamental plants like lily, orchids, Eucalyptus, Cinchona, blueberry, etc., and fruit trees like tomato, apple, banana, grapes, potato, Citrus, palm, etc.

Question 11.
Find out what the various components of the medium used for propagation of an explant in vitro are.
Solution:
The major components of the medium for in-vitro propagation are:

• Water
• Agar-agar
• Sucrose
• Inorganic salts
• Vitamins
• Amino acids
• Growth hormones like Auxin, Cytokinins.

Question 12.
Name any five hybrid varieties of crop plants which have been developed in India.
Solution:
Some of the hybrid varieties of plants in India are:

• Pusa Gaurav
• Pusa Sem 2
• Pusa Sem 3
• Pusa Sawani
• Pusa A-4

We hope the NCERT Solutions for Class 12 Biology Chapter 9 Strategies for Enhancement in Food Production help you. If you have any query regarding NCERT Solutions for Class 12 Biology Chapter 9 Strategies for Enhancement in Food Production, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 12 Physics Chapter 6 Electromagnetic Induction

NCERT Solutions for Class 12 Physics Chapter 6 Electromagnetic Induction are part of NCERT Solutions for Class 12 Physics. Here we have given. NCERT Solutions for Class 12 Physics Chapter 6 Electromagnetic Induction

Question 1.
Predict the direction of induced current in the situations described by the following Fig. 2(a) to (f).


Answer:
(a) By Lenz’s law, the face of the coil towards the south pole of the magnet opposes the south pole. So this face should behave as the south pole. Hence the current flows along qrpq.
(b) Similar to the above reason the current flows along yzxy and along prqp.
(c) When the coil is energised, with a cell the increasing current produces an inverse current in the nearby coil along yzxy.
(d) Similar to the above reason the current flows along zyvz.
(e) By Lenz’s law current is along xryx.
(f) Field lines being along the plane of the loop, there is no induced current.

Question 2.
Use Lenz’s law to determine the direction of induced current in the situations described by Figure:
(a) A wire of irregular shape turning into a circular shape;
(b) A circular loop being deformed into a narrow straight wire.


Answer:
When a wire of irregular shape turns into a circular (loop the magnetic flux linked with the loop increases due to an increase in area) The irregular shape. The induced e.m.f. will cause current to flow in such a direction, so that the wire forming the loop is pulled inward from all sides. It requires that the current should flow.
By applying Lenz’s Law, it follows that the current will flow in the direction a, d, c, b, a.

Question 3.
A long solenoid with 15 turns per cm has a small loop of area 2.0 cm² placed inside the solenoid normal to its axis. If the current carried by the solenoid changes steadily from 2.0 A to 4.0 A in 0.1s, what is the induced e.m.f. in the loop while the current is changing?
Answer:


Question 4.
A rectangular wire loop of sides 8 cm and 2 cm with a small cut ¡s moving out of a region of the uniform magnetic field of magnitude O.3 T directed normal to the mop. What ¡s the e.m.f. developed across the cut if the velocity of the loop is 1 cm s^-2 in a direction normal to the
(a) longer side,
(b) the shorter side of the loop? For how long does the induced voltage last in each case?
Answer:
e = Blυ

Question 5.
A 1.0 m long metallic rod is rotated with an angular frequency of 400 rad s^_1 about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field of 0.5 T parallel to the axis exists everywhere. Calculate the e.m.f. developed between the center and the ring.
Answer:

Question 6.
A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of 500 rad s^_1 a uniform horizontal magnetic field of magnitude 3.0 x 10^-2 T. Obtain the maximum and average emf induced in the coil. If the coil forms a closed loop of resistance 10 Ω, calculate the maximum value of current in the coil. Calculate the average power loss due to Joule heating. Where does this power come from?
Answer:

(v) Source of power loss is the external rotor which provides the necessary torque to rotate the coil.

Question 7.
A horizontal straight wire 10 m long extending from east to west is falling with a speed of 5.0 ms^-1, at right angles to the horizontal component of the earth’s magnetic field, 0.30 x 10^-4 Wb m^-2.
(a) What is the instantaneous value of the e.m.f. induced in the wire?
(b) What is the direction of the e.m.f.?
(c) Which end of the wire is at the higher electrical potential?
Answer:

(b) Using Fleming’s Right-hand rule, the direction of induced e.m.f. is from West to East.
(c) Since the rod will act as a source, the Western end will be at a higher electrical potential.

Question 8.
Current in a circuit falls from 5.0 A to 0.0 As. If an average emf of 200 V is induced, give an estimate of the self-inductance of the circuit.
Answer:

Question 9.
A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes from 0 to 20 A in 0.5 s, what is the change of flux linkage with the other coil?
Answer:
dΦ_B = M.dl = 1.5 x (20 – 0) = 30 Wb

Question 10.
A jet plane is travelling towards the west at a speed of 1800 km/h. What is the voltage difference developed between the ends of the wing having a span of 25 m, if the Earth’s magnetic field at the location has a magnitude of 5 x 10^-4 T and the dip angle is 30°?
Answer:

Question 11.
Suppose the loop in Exercise 6.4 is stationary but the current feeding the electromagnet that produces the magnetic field is gradually reduced so that the field decreases from its initial value of 0.3 T at the rate of 0.02 T s^-1. If the cut is joined and the loop has a resistance of 1.6 Ω, how much power is dissipated by the loop as heat? What is the source of this power?
Answer:

The Source of this power is the external agency which brings a change in a magnetic field.

Question 12.
A square loop of side 12 cm with its sides parallel to X and Y axes is moved with a velocity of 8 cm s^_1 in the positive x-direction in an environment containing a magnetic field in the positive z-direction. The field is neither uniform in space nor constant in time. It has a gradient of 10^-3 T cm^-1 along the negative x-direction (that is it increases by 10^-3 T cm^-1 as one moves in the negative x-direction), and it is decreasing in time at the rate of 10^-3 T s^_1. Determine the direction and magnitude of the induced current in the loop if its resistance is 4.50 mΩ.
Answer:


The direction of the induced current is such that it increases the magnetic flux linking with the loop in positive 2-direction.

Question 13.
It is desired to measure the magnitude of the field between the poles of a powerful loudspeaker magnet. A small flat search coil of area 2 cm² with 25 closely wound turns, is positioned normal to the field direction, and then quickly snatched out of the field region. Equivalently, one can give it a quick 90° turn to bring its plane parallel to the field direction. The total charge flew in the coil (measured by a ballistic galvanometer connected to the coil) is 7.5 mC. The combined resistance of the coil and the galvanometer is 0.50 Ω. Estimate the field strength of the magnet.
Answer:

Question 14.
The figure shows a metal rod PQ resting on the rails AB and positioned between the poles of a permanent magnet. The rails, the rod, and the magnetic field are in three mutually perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed-loop containing the rod = 9.0 mΩ. Assume the field to be uniform.

(a) Suppose K is open and the rod is moved with a speed of 12 cm s^-1 in the direction shown. Give the polarity and magnitude of the induced emf.
(b) Is there an excess charge built up at the ends of the rods when K is open? What if K is closed?
(c) With K open and the rod moving uniformly, there is no net force on the electrons in the rod PQ even though they do experience a magnetic force due to the motion of the rod. Explain.
(d) What is the retarding force on the rod when K is closed?
(e) How much power is required (by an external agent) to keep the rod moving at the same speed (= 12 cm s^_1) when K is closed? How much power is required when K is open?
(f) How much power is dissipated as heat in the closed-circuit? What is the source of this power?
(g) What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?
Answer:
Here, B = 0.50 T; 1 = 15 cm = 15 x 10^-2 m;
R = 9.0m Q = 9.0 x 10³ fl
(a) Now, e = Bvl
Here, V = 12 cm s^{-1 =} 12 x 10^-2 ms^-1
∴ e = 0.50 x 12 x 10-²x 15 x 10 ² = 9 x 10^-3V
If q is a charge on as electron, then the electrons in the rod will experience magnetic Lorentz force \(-q[\vec { v } +\vec { B } ]\) P. Q. Hence, the end P of the rod will become positive and the end Q will become negative.

(b) When the switch K is open, the electron collects at the end Q. Therefore, excess change is built up at the end Q. However, when the switch K is closed, the accumulated charge at the end Q flows through the circuit,

(c) The magnetic Lorentz force on the electron is cancelled by the electronic force acting on it due to the electronic field set up across the two ends due to the accumulation of positive and negative charges at the ends P and Q respectively.

(d) Retarding force, F = BIl =B \(\frac { e }{ R } \)

Question 15.
An air-cored solenoid with length 30 cm, area of cross-section 25 cm² and number of turns 500, carries a current of 2.5 A. The current is suddenly switched off in a brief time of 10^-3 s. How much is the average back emf induced across the ends of the open switch in the circuit ? Ignore the variation in magnetic field near the ends of the solenoid.
Answer:

Question 16.
(a) Obtain an expression for the mutual inductance between a long straight wire and a square loop of side a as shown in Figure

(b) Now assume that the straight wire carries a current of 50 A and the loop is moved to the right with a constant velocity, υ = 10 m/s. Calculate the induced e.m.f. in the loop at the instant when x = 0.2 m. Take a = 0.1 m and assume that the loop has a large resistance.
Answer:
(a) Consider a small portion of the coil of thickness dt at a distance t from the current-carrying wire. Then the magnetic field strength experienced by this portion

Question 17.
A line charge X per unit length is lodged uniformly onto the rim of a wheel of mass M and radius R. The wheel has light non-conducting spokes and is free to rotate without friction about its axis (Figure.) A uniform magnetic field extends over a circular region within the rim. It is given by

What is the angular velocity of the wheel after the field is suddenly switched off?

Answer:
Change in magnetic field is given by,

We hope the NCERT Solutions for Class 12 Physics Chapter 6 Electromagnetic Induction, help you. If you have any query regarding NCERT Solutions for Class 12 Physics Chapter 6 Electromagnetic Induction, drop a comment below and we will get back to you at the earliest.