CBSE Notes

By going through these CBSE Class 11 Physics Notes Chapter 2 Units and Measurement, students can recall all the concepts quickly.

Units and Measurement Notes Class 11 Physics Chapter 2

→ Physical Quantity = numerical value × unit = nu

→ Numerical value (n) ∝ \(\frac{1}{\text { size of unit(u) }}\)

→ Physical quantities which are independent of each other are called fundamental quantities.

→ Units of fundamental quantities are called fundamental units.

→ There are four systems of units namely FPS, CGS, MKS, and S.I. system.

→ 1 a. m.u.= 1.66 × 10^-27kg.

→ The product of n and u is called the magnitude of the physical quantity.

→ Force, thrust, and weight have the same SI unit, i.e. Newton.

→ Pressure, stress, and coefficient of elasticity have the same SI unit, i.e. Pascal.

→ The standard unit must not change with time and space. That is why the atomic standards for length and time have been defined.

→ The dimensions of many physical quantities especially those of heat, electricity, thermodynamics, and magnetism in terms of mass, length, and time alone become irrational, so SI is adopted which uses 7 basic units and two supplementary units.

→ The first conference on weights and measures was held in 1889.

→ Sevres near Paris is the headquarter of the International Bureau of Weights and Measures.

→ SI system was first adopted in the 11th general Conference of Weights and Measures in 1960.

→ S.I. system is also known as the rationalized M.K.S. system.

→ The various units of the S.I. system are rational in nature.

→ The various units of the S.I. system are coherent in nature.

→ It is wrong to say that the dimensions of force are [MLT^-2]. On the other hand, we should say that the dimensional formula for force is [MLT^-2].

→ The dimensional formula for the dimensionless physical quantity is written as [M°L°T°].

→ The dimensions of a physical quantity don’t depend on the system of units.

→ The dimensional formula is very helpful in writing the unit of a physical quantity in terms of the basic units.

→ The pure numbers are dimensionless.

→ Physical quantities defined as the ratio of two similar quantities are dimensionless.

→ The physical relations involving logarithm, exponential, trigonometric ratios, numerical factors, etc. cannot be derived by the method of dimensional analysis.

→ Physical relations involving addition or subtraction sign cannot be derived by the method of dimensional analysis.

→ If units or dimensions of two physical quantities are the same, these need not represent the same physical characteristics.

→ Torque and work have the same dimensions but have different physical characteristics.

→ Measurement is most accurate if its observed value is very close to the true value.

→ Significant figures are the number of digits up to which we are sure about their accuracy.

→ Significant figures don’t change if we measure a physical quantity in different units.

→ Significant figures retained after the mathematical operation (like addition, subtraction, multiplication, or division) should be equal to the minimum significant figures involved in any physical quantity in the given operation.

→ Error = Actual value: Observed value.

→ Absolute error: Δx_i = \(\overline{\mathrm{x}}\) – x_i

→ The absolute error in each measurement is equal to the least count of the measuring instrument.

→ Mean absolute error
Δx = \(\frac{1}{x} \sum_{i=1}^{n}\)(Δx₁)

→ When we add or subtract two measured quantities, the absolute error in the final result is equal to the sum of the absolute errors in the measured quantities.

→ When multiply or divide two measured quantities, the relative error in the final result is equal to the sum of the relative errors in the measured quantities.

→ For greater accuracy, the quantity with higher power should have the least error.

→ Smaller is the least count higher is the accuracy of measurement.

→ The relative error is a dimensionless quantity.

→ The unit and dimensions of the error are the same as that of the quantity itself.

→ The larger the number of significant digits after the decimal point in measurement, the higher is the accuracy of measurement.

→ Physical quantities: Physical quantities may be defined as the quantities in terms of which physical laws can be expressed and which can be measured directly or indirectly.

→ Subjective methods: The methods of measurement which depend on our senses are called subjective methods.

→ Objective methods: The methods of measurement which make use of scientific instruments are called objective methods.

→ Fundamental quantities: The quantities which are independent of each other and which are not generally defined in terms of other physical quantities are known as fundamental or basic quantities.

→ Derived quantities: The quantities whose defining operations are based on the fundamental physical quantities are called derived quantities.

→ Unit: A unit is defined as the reference standard of measurement.

→ If a number is without a decimal point and ends in one or more zeros, then all the zeros at the end of the number may not be significant.

→ To make the number, of Significant digits clear, it is suggested that the number may be written in exponential form.

→ For example, 20300 may be expressed as 203.00 × 10², to suggest that all the zeros at the end of 20300 are significant.

→ Fundamental or basic units: The basic units are those which can neither be derived from one another nor can be resolved into further units! For example units of length, mass and time, etc. These are 7 in number.

→ Derived units: The units of all those physical quantities which can be expressed in terms of fundamental units are called derived units. For example, units of velocity, force, and energy, etc.

→ Size of a physical quantity: The size of a physical quantity is determined by a unit and the number of times that unit is to be repeated to represent the complete quantity.
Size of a physical quantity = nu;
n = number of times the chosen unit is contained in the physical quantity,
u = size of the unit.

→ System of units: Complete set of units both for fundamental and derived quantities is known as a system of units.

→ S.I. Units: Systeme international of units, in short, is called S.I. units.
It has seven fundamental units namely

1. unit of length is meter (m),
2. kilogram (kg) unit of mass,
3. second (s) unit of time,
4. ampere (A) unit of current,
5. Kelvin (K) unit of temperature,
6. Candela (cd) unit of light intensity and
7. mol (mole) for a unit of amount of substance.

→ There are two supplementary units for measuring: (a) plane angle and solid angle. These are radian (rad) and steradian (sr) respectively.

→ θ(rad) = \(\frac{\text { arc }}{\text { radius }}=\frac{l}{r}\)

→ Ω(sr) = \(\frac{\text { surface area }}{(\text { radius })^{2}}=\frac{\Delta \mathrm{A}}{\mathrm{r}^{2}}\)

→ Length: It is defined as a measure of separation between two points in space.

→ Mass: It is the amount of substance contained in the body. Inertial mass: It is the mass of the body which is a measure of inertia F
∴ m = \(\frac{F}{a}\)

→ Gravitational mass: It is the mass of the body that determines the gravitational pull due to the earth acting on the body.
∴ m = \(\frac{W}{g}\)

→ Fermi (F): It is a unit of extremely small distances:
1 F = 10^-15 m.

→ Angstrom (A): It is the unit of length at the atomic level:
1 A = 10^-10 m ,

→ Astronomical unit (AU): It is the unit of length at a large scale:
1 A.U. = 1.496 × 10¹¹ m= 1.5 × 10¹¹ m.

→ Light year- It is defined as the distance traveled by light in one year
1 L.Y. = 9.46 × 10¹⁵ m.

→ Meter (m): Metre is the unit of length and is defined as the space occupied by 1,650,763.73 wavelengths of orange-red light emitted by krypton: 86 kept “at the triple point of nitrogen (radiation emitted due to transition between the levels 2P₁₀ and 5d₅).

→ Kilogram (kg): Kilogram is the unit of measurement of mass. It is the mass of international prototype platinum-iridium cylinders kept in the International Bureau of Weights and Measures at Sevres, France.

→ Second(s): It is the unit of time. A second is the duration of time corresponding to 9,192,631,770 vibrations corresponding to the transition between two hyperfine levels of cesium-133 atom in the ground state.

→ Ampere(A): An ampere of current is defined as the constant current, which when flowing through two straight parallel conductors of infinite length and negligible area of cross-section placed lm apart in air produces a force of 2 × 10^-7 Nm^-1.

→ Parsec: This unit is used to measure very large distances i.e., the distance between stars or galaxies.
1 Parsec = 3.08 × 10¹⁶m

→ Atomic mass unit (AMU): It is the unit of mass at the atomic and subatomic levels.
1 amu = \(\frac{\left(\text { mass of }_{6} C^{12} \text { atom }\right)}{12}\)

→ Dimensions: The dimensions of a physical quantity are the powers to which the fundamental units of length, mass and time have to be raised to obtain its units, e.g., dimensions of force [MLT^-2] are 1 in mass 1 in length and -2 in time.

→ Dimensional formula: Dimensional formula of a physical quantity is defined as the expression that indicates which of the fundamental units of mass, length, and time appear into the derived unit of that physical quantity and with what powers.

→ Dimensional equation: The equation obtained by equating the physical quantity to its dimensional formula is called the dimensional equation of that physical quantity.

→ Dimensional variables: The variable quantities which have dimensions are called dimensional variables! For example, velocity, force, momentum, etc.

→ Dimensionless variables: These are variable physical quantities that do not have dimensions. For example, relative density, specific heat, strain, etc.

→ Dimensional constants: Those constants which have dimensions are called dimensional constants. For example, gravitational constant, Planck’s constant.

→ Dimensionless constants: Those constants which do not have, dimensions are dimensionless constants. For example, all trigonometric functions, natural numbers 1, 2, 3…. π, e.

→ Significant figure: The significant figures are a measure of the accuracy of a particular measurement of a physical quantity. Significant figures in measurement are those digits in a physical quantity that are known reliably plus the one-digit which is uncertain.

→ Error: It is the difference between a true and measured value of a physical quantity.

→ Discrepancy: The difference between the two measured values of a physical quantity is known as a discrepancy.

→ Constant error: It is an error in measurements. It arises due to some constant causes such as faulty calibration on the instrument. This error remains constant in all observations.

→ Systematic error: This error is also a measurement error. The error is one that always produces an error of the same sign. This error may be due to imperfect technique, due to alteration of the quantity being measured, or due to carelessness and mistakes on the part of the observer.

→ Instrumental error: This is a constant type of error. These are errors of an apparatus and that of the measuring instruments used e.g., zero error in vernier calipers or screw gauge.

→ Error due to least count: This also is another type of constant error. The error due to the limitations imposed by the least counts of the measuring instruments comes under this heading.

→ Observational or Personal Error: This is a subheading of systematic error. This error is due to the experimental arrangement or due to the habits of the observer.

→ Error due to physical conditions: These errors are due to the experimental arrangement or due to the habits of the observer. These are also systematic errors.

→ Error due to unavoidable situations: These errors are due to the imperfectness of the apparatus or of non-availability of ideal conditions.

→ Random errors: The errors due to unknown causes are random errors.

→ Gross error: These types of errors are because of the carelessness of the observer.
These errors may be due to

• negligence towards sources of error due to overlooking of sources of error by the observer;
• the observer, without caring for least count, takes wrong observations;
• wrong recording of the observation.

→ Absolute error: The magnitude of the difference between the true value and the measured value is called absolute error.

→ A relative error: It is defined as the ratio of the mean absolute error to the true value.

→ Percentage error: The relative error expressed in percentage is percentage error.

→ Standard error: The error which takes into account all the factors affecting the accuracy of the result is known as the standard error.

→ Standard deviation: The root means the square value of deviations (the deviation of different sets of observations from the arithmetic mean) is known as standard deviation.
Standard deviation σ = \(\sqrt{\frac{\left(\mathrm{x}_{1}-\overline{\mathrm{x}}\right)^{2}+\left(\mathrm{x}_{2}-\overline{\mathrm{x}}\right)^{2}+\left(\mathrm{x}_{\mathrm{n}}-\overline{\mathrm{x}}\right)^{2}}{\mathrm{n}}}=\sqrt{\frac{\mathrm{S}}{\mathrm{n}}}\)

→ Probable error: The error calculated by using the principle of probability are probable errors. According to Bessels formula

→ Probable error e = ± 0.6745\(\sqrt{\frac{S}{n(n-1)}}\)

→ Standard error = \(\sqrt{\frac{\mathrm{S}}{n(n-1)}}\)

Important Formulae:
→ t = Size of oleic acid molecule = thickness of film of oleic acid
= \(\frac{\text { Volume of film }}{\text { Area of film }}\)

→ Inertial mass determination:
\(\frac{m_{1 i}}{m_{2 i}}=\frac{T_{1}^{2}}{T_{2}^{2}}\) where T₁ and T₂ are of the time of oscillation of inertia balance with inertial masses.

→ Gravitational mass determination:
\(\frac{\mathrm{w}_{1}}{\mathrm{w}_{2}}=\frac{\mathrm{m}_{\mathrm{g}_{1}}}{\mathrm{~m}_{\mathrm{g}_{2}}}\)
where m_g1 and m_g2 are gravitational masses.

→ Height by triangulation method:

1. The height of an accessible object, h = x tanθ, where θ = angle of elevation of the object at the point of observation at a distance x from it.
2. The height of the inaccessible object is:
   h = \(\frac{x}{\cot \theta_{2}-\cot \theta_{1}}\)
   where θ₁ and θ₂ are the angles made at two points of observation at distance x from each other.

→ Distance of stars (parallax method):
S = \(\frac{\mathrm{b}}{\theta}\), θ = Φ₁, + Φ₂, where Φ₁, and Φ₂, are the angles subtended by star on observer on Earth with an interval of 6 months.
θ = angle of parallax.
b = basis = distance between two points on the surface of earth.

→ n₂ = n₁ \(\left[\frac{\mathrm{m}_{1}}{\mathrm{~m}_{2}}\right]^{a}\left[\frac{\mathrm{L}_{1}}{\mathrm{~L}_{2}}\right]^{b}\left[\frac{\mathrm{T}_{1}}{\mathrm{~T}_{2}}\right]^{\mathrm{c}}\)

→ Distance by reflection method (Radar) is given by
d = \(\frac{c \times t}{2}\) where
c = velocity of light in vacuum
t = time in which it is covered twice.

→ d = \(\frac{\mathrm{ut}}{2}\) for Sonar, where u = velocity of sound waves.

→ Diameter of moon is D = Sθ, where θ is the angle made by the diameter of moon at the observer, S = distance of observer from the moon, D = diameter of moon or an astronomical object.

→ Radius of atom is r = \(\left(\frac{M}{2 \pi N \rho}\right)^{1 / 3}\)
Where N = Avogadro’s number
M = molecular weight of the substance
ρ = density of substance.

→ Relative error = \(\frac{\Delta \mathrm{x}}{\mathrm{x}}\)

→ % error = \(\frac{\Delta \mathrm{x}}{\mathrm{x}}\) × 100

→ Error in sum or difference form, ± Δz = ± Δp ± Δq

→ Maximum error in product or quotient form, \(\frac{\Delta z}{z}=\frac{\Delta p}{p}+\frac{\Delta q}{q}\)

→ % Error in power form,\(\frac{\Delta \mathrm{z}}{\mathrm{z}}\) × 100 = n\(\frac{\Delta \mathrm{p}}{\mathrm{p}}\) × 100

By going through these CBSE Class 11 Physics Notes Chapter 1 Physical World, students can recall all the concepts quickly.

Physical World Notes Class 11 Physics Chapter 1

→ Physics deals with nature and natural phenomenon.

→ Science is the knowledge acquired by man in an organised way.

→ The various steps involved in acquiring knowledge are:

1. systematic observations
2. reasoning
3. model making
4. a theoretical prediction.

→ The theory is the explanation of the behaviour of a physical system using a limited number of laws.

→ A theory is valid if it is able to explain satisfactorily most of the relevant measurements.

→ There is a certain amount of overlapping between Physics, Chemistry and Biology.

→ Advances in Physics are directly related to the advances in experimental observations.

→ Advances in Physics lead to the development of concepts.

→ A wide diversity in the physical world can be understood on the basis of a few concepts.

It is due to three reasons:
(a) Strict regularities and laws help in quantitative measurements.
(b) There is a small number of common and basic principles covering enormous diversities of scales of the phenomenon.
(c) It is easier to understand a phenomenon by separating important features from unimportant features.

→ The technological development of any society is very closely related to the application of Physics and other branches of science.

→ Measurements are the heart of Physics. In fact, Physics is also defined as the science of measurements.

→ Motion, energy, gravitation, properties of matter in bulk and their atomic origin, study of details of mechanical oscillations and waves, description of matter with a microscope all form a systematic study.

→ Science: An organised attempt of man to know and the knowledge he acquires is science.

→ Physics: It is the subject which deals with nature and natural phenomenon and their quantitative measurements.

→ Scientific method: Scientific method involves systematic observation, reasoning, model making and theoretical prediction altogether.

→ Theory: A scientific theory is the explanation of the natural phenomenon in terms of a limited number of laws.

→ Geocentric theory: It is a theory in which the earth is assumed to be at the centre of the universe.

→ Heliocentric theory: The sun is at the centre of the world consisting of Earth and other planets.

→ Corpuscular theory of light: Newton assumed light to be made up of corpuscles or particles.

→ Hydroelectric energy: Conversion of gravitational energy into ‘ electric energy through water.

→ Thermal power: Conversion of chemical energy of coal by burning it into electric energy.

→ Geothermal energy: It is the heat in the depth of the Earth.

→ Gravitational force: The force is an attraction between two masses is called the gravitational force. This force of attraction between the two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The constant of proportionality is called the Gravitational constant or constant of gravitation G.
F = G\(\frac{m_{1} m_{2}}{r^{3}}\)r̂
Its scalar form is F = G\(\frac{m_{1} m_{2}}{r^{2}}\)

→ Constant of gravitation ‘G’: It is equal to the force of attraction acting between two masses each of 1 kg placed 1 m apart in the air.

→ Electromagnetic force: The combined electrostatic and magnetic force between charged particles and magnetic poles is called electromagnetic force.

→ Nuclear or strong forces: The strong attractive forces between particles in a nucleus are called nuclear forces. This force can act within a distance of 10-15m. These forces are charge independent
i. e. even a proton attracts another proton.

→ Weak forces: The forces of interaction between elementary particles are weaker than the strong forces and these activities within a distance of about 10^-12 m.

Studying from CBSE Class 11th Physics Revision Notes helps students to prepare for the exam in a well-structured and organised way. Making Class 11 Physics NCERT Notes saves students time during revision as they don’t have to go through the entire textbook. In CBSE Notes, students find the summary of the complete chapters in a short and concise way. Students can refer to the NCERT Solutions for Class 11 Physics, to get the answers to the exercise questions.

Physics Class 11 NCERT Notes | Notes of Physics Class 11

Notes of Physics Class 11 | NCERT Notes for Class 11 Physics

1. Physical World Class 11 Notes
2. Units and Measurement Class 11 Notes
3. Motion in a Straight Line Class 11 Notes
4. Motion in a Plane Class 11 Notes
5. Law of Motion Class 11 Notes
6. Work, Energy and Power Class 11 Notes
7. Systems of Particles and Rotational Motion Class 11 Notes
8. Gravitation Class 11 Notes
9. Mechanical Properties of Solids Class 11 Notes
10. Mechanical Properties of Fluids Class 11 Notes
11. Thermal Properties of Matter Class 11 Notes
12. Thermodynamics Class 11 Notes
13. Kinetic Theory Class 11 Notes
14. Oscillations Class 11 Notes
15. Waves Class 11 Notes

We hope students have found these 11th Class Physics Notes Pdf Download useful for their studies. If you have any queries related to Physics Notes for Class 11 Pdf, drop your questions below in the comment box.

By going through these CBSE Class 12 Chemistry Notes Chapter 16 Chemistry in Everyday Life, students can recall all the concepts quickly.

Chemistry in Everyday Life Notes Class 12 Chemistry Chapter 16

Medicines: Medical chemistry deals with the design and synthesis of drugs based on an undertaking of how these work in our body.

Drugs are chemicals of low molecular mass (~ 100-500 μ). They interact with macromolecular targets and produce a biological response. When the biological response is effective and useful, these chemicals are called medicines and are used in the treatment, diagnosis, and prevention of diseases. In larger doses than recommended, they are potential poisons. The use of chemicals for therapeutic effect is called Chemotherapy.

Designing of a Drug: Two considerations arise

1. Drug target,
2. drug metabolism.

1. Drug target: The biological macromolecules such as carbohydrates lipids, proteins, nucleic acids with which drugs interact are called targets. The correct choice of the molecular target for a drug is important to obtain a desired therapeutic effect.

2. Drug metabolism: A drug travels through the body in order to reach the target. So its design should be such that it reaches the target without being metabolized in between. Also, after its action, it should be excreted without causing harm to the body.

Compounds from which drugs are designed are called lead compounds. These lead compounds may be obtained from natural sources such as plants, trees, bushes, venoms, and metabolites of microorganisms or they may be synthesized in order to improve drug activity and to have minimum side effects, mechanisms of drug action in the biological systems are also considered while drug designing.

Classification of Drugs:
1. On the basis of Pharmacological effect: It is useful for doctors. For example, analgesics have a pain-killing effect, antiseptics kill or arrest the growth of microorganisms.

2. On the basis of action on a particular biochemical process: All antihistamines inhibit the action of the compound histamine, which causes inflammation in the body.

3. On the basis of chemical structure: Drugs classified in this way share common structural features and often have similar pharmacological activity. For example, sulphonamides have common structural features given below and are mostly antibacterial.

(Sfructuralfratures of Suiphona mides)

4. On the basis of molecular targets: This classification is most useful for medicinal chemists. Various enzymes and receptors in the cell are some of the common drug targets.

Interaction of drugs with targets: Proteins that perform the role of biological catalysts in the body are called enzymes. Proteins that are important to a communication system in the body are called receptors. Tires enzymes and receptors serve as drug targets among others.

Enzymes as Drug Targets:
(a) Catalytical activity of enzymes: Enzymes perform two major functions:
1. The first function of an enzyme is to hold the substrate for a chemical reaction. Active sites of enzymes hold the substrate molecule in a suitable position so that it can be attacked by the reagent effectively.

Substrates bind to the amino acid residues of the protein present on the active site of the enzyme through a variety of interactions such as ionic bonding, hydrogen bonding, van der Waals interaction of dipole-dipole interaction (Fig.).

These binding interactions should be strong enough to hold the substrate long enough so that the enzyme can catalyze the reaction, but weak enough to allow the products to depart after their formation.

(a) Active site of an enzyme,
(b) substrate
(c) Substrate held in the active site of the enzyme

(a) The second function of the enzyme is to provide functional groups that will attack the substrate and carry out a chemical reaction. This function is carried out by some other amino acid residues of protein present on the active site of the enzyme.

These provide free functional groups to attack the substrate and bring about chemical reactions. For example, if amino acid, serine is present nearby the substrate held on the active site, then its – OH group is free to act as a nucleophile in the enzyme-catalyzed reaction.

(b) Interaction of drugs with enzymes: Drugs inhibit the activity of the enzymes and so are called Enzyme Inhibitors. Enzyme inhibitors can block the binding site and prevent the binding of substrate or these can inhibit the catalytical activity of the enzyme.

(c) Prevention of attachment of natural substrate in the active site by drugs: Drugs inhibit the attachment of substrate on the active site of enzymes in two different ways explained below:

Drugs compete with the natural substrate for the active sites. Such drugs are called competitive inhibitors.

(Drug and substrate competing for the active site)

2. On the other hand, some drugs do not bind to the active site. These bind to a different site of enzyme which is called the allosteric site. This binding of inhibitors at the allosteric sites changes the shape of the active site in such a way that the substrate cannot recognize it.

[Noncompetitive inhibitor changes the active site of the enzyme after binding at the allosteric site]

If the bond formed between enzyme and inhibitor is a strong covalent bond and cannot be broken easily then the enzyme is blocked permanently. The body then degrades the enzyme inhibitors complex and synthesizes new enzymes.

Receptors as Drug Targets:
→ Location of receptor in the animal cell: Receptors are proteins that are crucial to the body’s communication process. The majority of these are embedded in cell membranes.

Receptor proteins are embedded in the cell membrane in such a way that their small part possessing active site projects out of the surface of the membrane and opens on the outer region of the cell membrane.

→ Transfer of message into the cell by receptors: Neurotransmitters communicate messages in the body between the 3 neurons and that between neurons to muscles. These chemical messengers are received at the binding site of the receptor protein. To accommodate messenger, the shape of the receptor changes. This brings about the transfer of the message into the cell. Thus, chemical messenger gives a message to the cell without entering the cell.

Two types of chemical messengers are involved in the message transfer:

1. Hormones
2. neurotransmitters

1. Hormones: Adrenaline (epinephrine) is an example of hormone. It is released from the adrenal medulla in situations of stress or danger.

2. Neurotransmitters are small molecules such as acetylcholine, dopamine, and serotonin.


→ Interaction of Drugs: Receptors that interact with one specific chemical messenger may differ slightly in their binding sites.

For example, there are two types of adrenergic receptors named a-adrenergic receptors and β-adrenergic receptors. These differ slightly in the structure of their binding sites, but both of these receptors can bind epinephrine.

Drugs that bind to the receptor site and inhibit its natural function are called antagonists. There are other types of drugs that mimic the natural messenger by switching on the receptor. They are called agonists.

→ Side-effects caused by drugs: Side effects are caused when a drug binds to more than one type of receptor, e.g., the serotonin receptor is a target for some anti-depressant drugs. Side effects can arise if the drug interacts with histamine or acetylcholine.

Types erf Drugs:
1. Antacids: If acid is produced in excess in the stomach, it causes irritation and pain and in severe cases, ulcers are produced. Histamine stimulates the secretion of pepsin and hydrochloric acid. A drug like cimetidine (Tagamet) and ranitidine (Zantac) was designed to prevent the interaction of histamine with the receptors present in the stomach wall. This resulted in the release of a lesser amount of acid.

2. Antihistammines: Histamine is a potent vasodilator. It has various functions. It contracts the smooth muscles in the bronchi and gut and relaxes other muscles. It is also responsible for the nasal congestion associated with common colds and allergic response to pollen. Synthetic drugs brompheniramine (Dimetapp) and terfenadine (Seldane) act as antihistamines.

The above-mentioned antihistamines do not affect the secretion of acid in the stomach. It is because that antiallergic and antacid drugs work on different receptors.

3. Neurologically Active Drugs: Tranquilizers and analgesics are neurologically active drugs.

These affect the message transfer mechanism from the nerve to the receptor.
(a) Tranquilizers are a class of compounds used for the treatment of stress, mild and severe mental diseases. They relieve stress, anxiety irritability, and excitement by inducing a sense of well-being.

→ They act on the central nervous system (CNS): Noradrenaline is one of the neurotransmitters that plays role in mood changes. If its level is low for some reason, the signal sending activity becomes low and the person suffers from depression.

Antidepressant drugs, in such cases, inhibit the enzymes which catalyze the degradation of noradrenaline. If the enzyme is inhibited, this important neurotransmitter is slowly metabolized and can activate its receptor for longer periods of time, thus countering the effect of depression. Iproniazid and phenelzine are two such drugs.

Some tranquilizers namely, Chlorodiazepoxide and Meprobamate are relatively mild tranquilizers suitable for relieving tension. Equanil is used in controlling depression and hypertension.


→ Barbiturates: The derivatives of barbituric acid are hypnotic- sleep-producing agents. Some of them are Veronal, Valium and Serotonium.

(b) Analgesics: are the drugs that reduce or abolish pain without causing impairment of consciousness, mental confusion, or some other disturbance of the nervous system.

They are of two types:
1. Non-narcotic (non-addictive) drugs: Aspirin and paracetamol belong to the class of non-addictive analgesics. These drugs have many other effects such as reducing fever (antipyretic) and preventing platelet coagulation. Aspirin is helpful to prevent heart attacks,

2. Narcotic analgesics: like morphine, heroin, codeine relieve pain and produce sleep in medicinal doses, and in excess are fatal. These analgesics are chiefly used for the relief of post-operative pain, cardiac pain, and pains of terminal cancer and in childbirth.

4. Antimicrobials: Disease may be caused by bacteria, viruses, etc. P. Ehrlich who developed the medicine Salvarsan for the treatment of syphilis found that the -As = As – linkage present in arsphenamine (salvarsan) resembles the -N = N- linkage present in azo-dyes in the sense that N atom is present in place of As. He was successful in 1932 in preparing the first effective antibacterial agent Prontosil which resembles the structure of the compound salvarsan.

[The structures of salvarsan and prontosil and azo dye showing structural similarity]

This led to the study of the relation between structure and activity. It was found that part of the proposal molecule (shown in the box) in the form of p-amino benzene sulphonamide (Sulphanilamide) has antibacterial activity. The led to the discovery of Sulpha drugs.

Antimicrobials control microbial diseases in three ways:
(a) a drug that kills the organism in the body (bactericidal).
(b) a drug that inhibits or arrests the growth of organisms (bacteriostatic) and
(c) increasing immunity and resistance to infection in the body,

5. Antibiotics: It is a substance (produced wholly or partly by chemical synthesis) that in low concentration inhibits the growth or destroys microorganisms by intervening in their metabolic processes.

The first antibiotic discovered by Alexander Fleming’s Penicillin from the mold Penicillium Notatum.

The antibiotics can be either bactericidal or bacteriostatic.

Broad Spectrum antibiotics are medicines effective against several types of harmful microorganisms, e.g., tetracycline, chloramphenicol.

6. Antiseptics and disinfectants: Antiseptics and disinfectants are also the chemicals which either kill or prevent the growth of microorganism.

Antiseptics are applied to living tissues such as wounds, cuts, ulcers, and diseased skin surfaces. Examples are Furacine, Soframicine, etc. Dettol is a mixture of Chloroxylenol and terpineol. Bithinol is added to soaps to impart antiseptic properties. Iodine is a powerful antiseptic. Its 2-3% solution in alcohol-water solution is known as tincture of iodine. It is applied to wounds. Iodoform is also used as an antiseptic for wounds. Boric acid (H3P03) in dilute solution (aqueous) is a weak antiseptic for the eyes.

Disinfectants are applied to inanimate objects such as floors, drainage systems, instruments, etc. The same substance can act as an antiseptic as well as a disinfectant by varying the concentration. For example, 0.2 percent situation of phenol is an antiseptic while it’s one percent solution is disinfectant.

Chlorine in the concentration of 0.2 to 0.4 ppm and S02 in very low concentration are disinfectants.

7. Antifertility Drugs: Norethindrone is an example of synthetic progesterone (a type of hormone) derivative most widely used as an antifertility drug for birth control. The estrogen derivative is used in combination with progesterone derivative is ethynylestradiol (Novestrol).

→ Chemicals in Food: To enhance the shelf life of food to make it more appealing and sometimes more nutritive, chemicals are added to it.

They are:

1. Food colors,
2. Flavors and sweeteners,
3. Fat emulsifiers and stabilizing agents,
4. Flour improvers antistaling agents and bleaches,
5. Antioxidants,
6. Preservatives,
7. Nutritional supplements such as minerals, vitamins, and amino acids.

Except for category (7), none of the chemical additives have any nutritive value.

→ Artificial Sweetening agents: Ortho-Sulphobenzimide (saccharine)

is an artificial sweetener and mass/mass, it is 550 times as sweet as cane sugar. It is excreted from the body in the urine unchanged and appears to be entirely harmless and inert and so is of great value to diabetic persons and people who need to control the intake of calories.

Other artificial sweeteners are aspartame (100 times sweet as sugar), sucralose (600 times) alitame (2000 times as sweet as sugar).

→ Preservatives: In addition to class I preservatives like salts, sugar, and vegetable oils, the most common class II preservative is sodium benzoate

which is used in limited quantities and is metabolized in the body.

→ Chemistry of Cleansing Agents:
1. Soaps: Soaps are sodium or potassium salts of long-chain fatty acids, e.g., stearic acid, oleic acid, and palmitic acid. Soaps are obtained by the saponification of triglycerides of fatty acids.

Potassium soaps are softer than sodium soaps.

Types of Soaps: Toilet Soaps are prepared by using better grades of fats and oils and excess alkali is removed. Colour and perfumes are added. Transparent Soap is made by dissolving the soap in ethanol and then evaporating the excess solvent.

In medicated soaps, substances of medicinal value are added. ! Shaving soaps contain glycerol to prevent rapid drying. Laundry soaps t contain fillers like sodium proximate, sodium silicate borax, and sodium \ carbonate.

Soaps do not work in hard water as soaps react with Ca²⁺ and Mg²⁺ ions present in hard water to produce curdy precipitate or scum,

2. Soapless detergents: Soapless detergents are cleansing agents; which have all the properties of soaps, but they actually do not contain; soap. They are useful in hard water also.

Synthetic detergents are mainly of three types:

1. Anionic detergents
2. Cationic detergents
3. Non-ionic detergents

1. Anionic Detergents are sodium salts of sulfonated long-chain alcohols.

In anionic detergents, the anionic part of the molecule is involved in the cleansing action.

2. Cationic Detergents: Cationic detergents are acetates, chlorides, or bromides of quaternary ammonium salts. An example is cetyltrimethylammonium bromide:

Cationic detergents are expensive and due to their germicidal properties, they are used as hair conditioners.

3. Non-ionic Detergents: Stearic acid reacts with polyethylene glycol to form non-ionic detergents.

Liquid dishwashing detergents are non-ionic types. Detergents containing highly branched hydrocarbon chains are not easily biodegradable.

By going through these CBSE Class 12 Chemistry Notes Chapter 15 Polymers, students can recall all the concepts quickly.

Polymers Notes Class 12 Chemistry Chapter 15

Polymers are macromolecules having high molecular mass [10³ – 10⁷ p]. They are formed by joining repeating structural units on a large scale. The repeating structural units are derived from some simple and reactive molecules known as monomers and are linked to each other by covalent bonds. The process of the formation of polymers from respective monomers is called polymerisation.

Classification of Polymers:
A. Based on the source.

1. Natural Polymers: These are found in plants and animals. Examples are proteins, cellulose, starch, resins and rubber.
2. Semi-synthetic Polymers: Cellulose acetate (rayon) and cellulose nitrate are examples of this category.
3. Synthetic Polymers: Polyethene; nylon 6, 6; Buna-S are examples of man-made polymers.

B. Based on the structure of Polymers:
1. Linear Polymers: These polymers Consist of long and straight-chain repeating units derived from the monomers. The examples are high-density polyethene, polyvinyl chloride (PVC) etc. These are schematically represented as

2. Branched Chain Polymers: These polymers contain linear chains having some branches, e.g., low-density polyethene.

3. Cross-linked or Network Polymers: These are usually formed from bifunctional and trifunctional monomers, e.g., bakelite, melamine etc.

C. Classification Based on mode of Polymerisation:
1. Addition Polymers: The addition polymers are formed by the repeated addition of monomer molecules possessing double or triple bonds, e..g, the formation of polyethene from ethene and polypropene from propene. In addition, polymers obtained from the same monomer are called Homopolymers, e.g., Polyethene.

If two different units of monomers get added, they are called copolymers, e.g., Buna-S, Buna-N,

2. Condensation Polymers: The condensation polymers are formed by repeated condensation reaction between two monomeric units having different bifunctional and trifunctional groups with the elimination of small molecules like water, alcohol, hydrogen chloride etc. The formation of Nylon 6,6 is an example.

D. Classification based upon molecular forces:
1. Elastomers: These are rubber-like solids with elastic properties. The polymer chains are held together by weak intermolecular forces. They can be easily stretched. Examples are Buna-S, Buna-N, Neoprene etc.

2. Fibres: The intermolecular forces between the chains are strong hydrogen bonds. They have large tensile strength and are used to form thread forming crystalline solids. The examples are Nylon 6, 6 and polyesters.

3. Thermoplastic Polymers: In these polymers, the intermolecular forces are intermediate between those of elastomers and fibres. In these polymers, there is cross-linking between the chains. They soften on heating and harden on cooling. Common examples are polyethene, polystyrene polyvinyls etc.

4. Thermosetting Polymers: These polymers are cross-linked or heavily branched molecules, which on heating undergo expensive cross-linking in moulds and become infusible. They cannot be reused again. Common examples are bakelite and urea-formaldehyde resins etc.

E. Classification based on Growth Polymerisation: The addition and condensation polymers are nowadays also referred to as chain-growth polymers and step-growth polymers depending upon the type of polymerisation mechanism they undergo during their formation.

Types of Polymerization:
1. Addition Polymerization or Chain growth Polymerization: Here molecules of the same or different monomers add together on a large scale to form a polymer. It can proceed through the formation of free radicals or ionic species.
(a) Free Radical Mechanism: A variety of alkenes or dienes and their derivatives are polymerised in the presence of a free radical generating initiator (catalyst) like benzoyl chloride.

It consists up of the following three steps.
1. Chain-initiation Step:

2. Chain propagating step:

3. Chain terminating step:

(b) Preparation of some important Addition Polymers:
1. Polyethene: There are two types of polyethenes as given below:
1. Low-Density Polyethene (LDPE]:

It is chemically inert and tough, but flexible and a poor conductor of electricity. It is used in the insulation of electric wires and the manufacture of squeeze bottles, toys and flexible pipes.

2. High-Density Polyethene (HDPE):

It has a high density. It is also chemically inert and tougher and harder. It is used for making buckets, dustbins, bottles and pipes.

2. Polytetrafluoroethene (Teflon):

Chemically inert, it is resistant to attack by corrosive reagents. Used for making oil seals, gaskets and non-stick surface coated utensils.

3. Polyacrylonitrile:

It is used as a substitute for wool in making fibres like Orlon or Acrilan.

→ Condensation Polymerization or Step-Growth polymerization: It involves a repetitive condensation reaction between two bifunctional monomers. It may result in the loss of simple molecules as H₂O, alcohol etc.

1. Polyamides: Preparation of Nylons
1. Nylon 6,6:

It is used in making sheets, bristles for brushes and in the textile industry.

2. Nylon 6: It is obtained by heating caprolactam with water at high temperature.

Nylon 6 is used for the manufacture of tyre cords, fabrics and ropes.

2. Polyesters: These are the polycondensation products of dicarboxylic acids and diols. The formation of terylene or dacron by the reaction between ethylene glycol and terephthalic acid is an example.

Dacron fibre (terylene) is crease-resistant and is used in blending with cotton and wool fibres and also as glass reinforcing materials in safety helmets etc.

3. Phenols formaldehyde polymer (Bakelite and related polymers): Phenol reacts with formaldehyde in the presence of dil. acid or base.

Novolac (used in paints) on heating with HCHO undergoes cross-linking to form an infusible solid mass called bakelite

It is used for making combs, photograph records, electrical switches and handles of various utensils.

4. melamine-formaldehyde polymers: It is obtained by the condensation polymerisation of melamine and formaldehyde.

It is used in the manufacture of unbreakable cups and plates.

Copolymerization: A mixture of 1,3-butadiene and styrene form a copolymer: Butadiene-Styrene copolymer.

1. Natural rubber: It possesses elastic properties. It is a linear polymer of isoprene (2-methyl-l, 3-butadiene).

It is also called cis-1, 4-polyisoprene. It consists of various chains held together by weak van der Waals forces and has a coiled structure.

→ Vulcanisation of Rubber: To improve upon the physical properties of natural rubber, its vulcanisation is carried out. It consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373-415 K. On vulcanization sulphur forms cross-links at the reactive sites of double bonds and the rubber gets Stiffened. The probable structure of vulcanised rubber is:

→ Synthetic Rubber: Synthetic rubbers are either homopolymers of 1, 3-butadiene derivatives or are copolymers of 1, 3-hutadíene or its derivatives with another unusual rated monomer.

1. Neoprene: It has superior qualities to natural rubber. It has better resistance to vegetable and mineral oils. It is used for the manufacture of conveyor belts, gaskets and hoses.

2. Buna-N: It is a copolymer of 1,3-butadiene and acrylonitrile in the presence of a peroxide catalyst.

It is resistant to the action of petrol, lubricating oil and organic St .h ents. It is used is making oil seals tank living etc.

→ Molecular Mass of Polymers: Polymer properties are closely related to their molecular mass, size and structure. Its molecular mass is always expressed as an average.

It can be determined by chemical and physical methods.

1. Weight-average molecular mass
2. Number-average molecular mass.

→ Biodegradable Polymers: A large number of polymers are non-biodegradable and are the reuse for environmental pollution. Nowadays, certain new biodegradable synthetic polymers have been designed and developed. Aliphatic polyesters are one of the important class of biodegradable polymers, e.g.,

→ Poly β-hydroxybutyrate-co-β-hydroxy valerate (PHBV): It is obtained by the copolymerisation of 3-hydroxybutyric acid and 3-hydroxy pentanoic acid.

PHBV undergosbateria1 degradation in the environment.

→ Nylon-2-Nylon 6: It is an alternating polyamide copolymer of glycine (H₂N—CH₂—COOH) and aminocaproic acid. (H₂N (CH₂)₅ COOH) and is biodegradable.

Some other commercially important Polymers along with their structures and uses are given below in the table: