Magnetism and Matter Class 12 MCQs Questions with
Magnetism And Matter Class 12 MCQ Question 1.
A toroid of n turns, mean radius R and cross-sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. Its magnetic moment m
(A) is non-zero and points in the z-direction by symmetry.
(B) points along the axis of the toroid (m = mø ).
(C) is zero, otherwise there would be a field falling as \(\frac{1}{r^{3}}\) at large distances outside the toroid,
(D) is pointing radially outwards.
Answer:
(C) is zero, otherwise there would be a field falling as \(\frac{1}{r^{3}}\) at large distances outside the toroid,
Explanation:
As we know that a toroid can be considered as a ring shaped closed solenoid.
So that it is like an endless cylindrical solenoid. So, the magnetic field is only confined inside the body of a toroid in the form of concentric magnetic lines of force. For any point inside, the empty space surrounded by toroid and outside the toroid, the magnetic field B is zero because the net current enclosed in these spaces is zero. So that, the magnetic moment of toroid is zero. In general, if we take r as a long distance outside the toroid, the m cc but this case is not possible here.
Class 12 Physics Chapter 5 MCQ Question 2.
Consider the two idealized systems : (i) a parallel plate capacitor with large plates and small separation and (ii) a long solenoid of length L, R, radius of cross-section. In (i), E is ideally treated as a constant between plates and zero outside. In (ii), magnetic field is constant inside the solenoid and zero outside. These idealized assumptions, however, contradict fundamental laws as below :
(A) Case (i) contradicts Gauss’s law for electrostatic fields.
(B) Case (ii) contradicts Gauss’s law for magnetic fields.
(C) Case (i) agrees with ∮E.dl = 0
(D) Case (ii) contradicts ∮H.dl = Im
Answer:
(B) Case (ii) contradicts Gauss’s law for magnetic fields.
Explanation:
According to Gauss’s law of electrostatic field,
∮E.ds = \(\frac{q}{\varepsilon_{0}}\)
So it does not contradict for electrostatic field as the electric field lines do not form continuous path.
According to Gauss’s law of magnetic field,
∮B.ds = 0
It is clear that it contradicts for magnetic field because there is magnetic field inside the solenoid, and no field outside the solenoid carrying current, but the magnetic field lines form the closed paths.
Magnetism And Matter MCQ Chapter 5 Question 3.
A rod of length L, along east-west direction is dropped from a height H. If B be the magnetic field due to Earth at that place and angle of dip is 0, then the magnitude of the induced e.m.f. across two ends of the rod when the rod reachs the Earth is –
(A) BLH cos θ
(B) BL cos θ x (2gH)1/2
(C) BL cos θ / (2gH)1/2
(D) None of the above
Answer:
(B) BL cos θ x (2gH)1/2
Explanation:
Horizontal component of magnetic field = B cos θ
Velocity of the rod = (2 gH)1/2
Induced e.m.f. = BLυ = BL cos θ x (2 gH)1/2
Chapter 5 Physics Class 12 MCQ Question 4.
A coil of N turns and radius R carries a current I. It is unwound and rewound to make a square coil of side a having same number of turns (N). Keeping the current I same, the ratio of the magnetic moments of the circular coil and the square coil is –
(A) \(\pi \frac{\mathrm{R}^{2}}{a^{2}}\)
(B) \(\pi \frac{a^{2}}{R^{2}}\)
(C) \(\frac{\mathrm{R}^{2}}{a^{2}}\)
(D) None of the above
Answer:
(A) \(\pi \frac{\mathrm{R}^{2}}{a^{2}}\)
Explanation:
Ch 5 Physics Class 12 MCQ Question 5.
A magnetic dipole moment is a vector quantity directed from:
(A) South to North
(B) North to South
(C) East to West
(D) West to East
Answer:
(A) South to North
Explanation:
Magnetic dipole moment vector is directed from South pole to north pole.
Magnetism MCQ Class 12 Question 6.
Time period of oscillation of a magnetic needle is –
(A) T = \(\sqrt{\frac{I}{M B}}\)
(B) T = \(2 \pi \sqrt{\frac{I}{M B}}\)
(C) T = \(2 \pi \sqrt{\frac{\mathrm{MB}}{\mathrm{I}}}\)
(D) T = \(\pi \sqrt{\frac{\mathrm{MB}}{\mathrm{I}}}\)
Answer:
(B) T = \(2 \pi \sqrt{\frac{I}{M B}}\)
Explanation:
Time period of oscillation of a magnetic needle is T = \(2 \pi \sqrt{\frac{I}{M B}}\)
Physics Class 12 Chapter 5 MCQ Question 7.
A magnetic needle is kept in a non-uniform magnetic field experiences
(A) a force as well as a torque
(B) a torque but not a force
(C) a force and a torque
(D) a force but not a torque
Answer:
(A) a force as well as a torque
Explanation:
Field being non-uniform the poles of the needle will experience non-uniform forces. Hence, the needle experiences a force as well as a torque.
MCQ On Magnetism Class 12 Question 8.
The magnetic field of Earth can be modelled by that of a point dipole placed at the centre of the Earth. The dipole axis makes an angle of 11.3° with the axis of Earth. At Mumbai, declination is nearly zero. Then,
(A) the declination varies between 11.3° W to 11.3° E.
(B) the least declination is 0°.
(C) the plane defined by dipole axis and Earth axis passes through Greenwich.
(D) declination averaged over Earth must be always negative.
Answer:
(A) the declination varies between 11.3° W to 11.3° E.
Explanation:
The magnetic field lines of the Earth resemble that of a hypothetical magnetic dipole located at the centre of the Earth.
The axis of the dipole does not coincide with the axis of rotation of the Earth and it is tilted at some angle (angle of declination).
In this situation, the angle of declination is approximately 11.3° with respect to the later. So, there is two possibilities arises as shown :
So that the declination varies between 11.3° W to 11.3° E.
MCQ Of Chapter 5 Physics Class 12 Question 9.
Let the magnetic field on Earth be modelled by that of a point magnetic dipole at the centre of Earth. The angle of dip at a point on the geographical equator
(A) is always zero.
(B) is always positive
(C) is always negative
(D) can be positive or negative or zero.
Answer:
(D) can be positive or negative or zero.
Explanation:
Angle of inclination or dip is the angle between Ihe direction of intensity of total magnetic field of the Earth and a horizontal line in the magnetic meridian. If the total magnetic field of the Earth is modelled by a point magnetic dipole at the centre, then it is in the same plane of geography al collator, line- the angle of dip on the geographical equator will he Jifferenl at dillerent point*. It m.iv be positive or negalive or may be zero at some points.
Magnetism Class 12 MCQ Chapter 5 Question 10.
Relative permeability of a magnetic material is 0.5. The material is –
(A) diamagnetic.
(B) ferromagnetic.
(C) paramagnetic.
(D) not a magnetic material.
Answer:
(A) diamagnetic.
Explanation:
Relative permeability of diamagnetic magnetic material is less than 1.
MCQ On Magnetism Class 12 Pdf Question 11.
Which of the following relation is correct?
(A) B = BV x BH
(B) B = BV / BH
(C) B = BV + BH
(D) B = \(\sqrt{B_{\mathrm{V}}^{2}+B_{\mathrm{H}}^{2}}\)
Answer:
(D) B = \(\sqrt{B_{\mathrm{V}}^{2}+B_{\mathrm{H}}^{2}}\)
Explanation:
BH – B cos θ
BV = B sin δ
B = \(\sqrt{B_{\mathrm{V}}^{2}+B_{\mathrm{H}}^{2}}\)
Class 12 Physics Ch 5 MCQ Question 12.
Ratio of total intensity of magnetic field at equator to poles is
(A) 1 : 1
(B) 1 : 2
(C) 2 : 1
(D) None of the above
Answer:
(A) 1 : 1
Explanation:
BH = B cos θ BV = BH sin δ
At equator, δ = 0°.
So, BH = B, BV = – 90°
At poles, δ = 90°.
So, BH = – B, BV = B
So, the ratio of total intensity of magnetic field at equator to poles is 1 :1.
MCQ On Magnetism And Matter Chapter 5 Question 13.
Which of the following is most suitable for the core of an electromagnet?
(A) Soft iron
(B) Steel
(C) Alnico
(D) Copper
Answer:
(A) Soft iron
Explanation:
Soft Iron gels magnetized faster but loses its magnetism as soon as the current slops flowing in solenoid. Icnce soft iron is said to have high susceptibility but low retentivily. This property of soft iron makes it suitable for core of electromagnets where we need strong but temporary magnetism as long as current is flowing.
Physics Chapter 5 Class 12 MCQ Question 14.
A ferromagnetic substance is heated above its curie temperature. Which of the following statements is correct?
(A) Ferromagnetic domains get perfectly arranged.
(B) Ferromagnetic domains get randomly arranged.
(C) Ferromagnetic domains are not at all influenced.
(D) Ferromagnetic material transforms into diamagnetic substance.
Answer:
(B) Ferromagnetic domains get randomly arranged.
Explanation:
On heating above Curie temperature, Ferromagnetic domains get randomly arranged and it transforms into paramagnetic substance.
Assertion And Reason Based MCQs (1 Mark each)
Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
(A) Both A and R are true and R is the correct explanation of A
(B) Both A and R are true but R is NOT the correct explanation of A
(C) A is true but R is false
(D) A is false and R is true
Class 12 Chapter 5 Physics MCQ Question 1.
Assertion (A): The magnetic field configuration with 3 poles is not possible.
Reason (R): No torque acts on a bar magnet itself due to its own field.
Answer:
(B) Both A and R are true but R is NOT the correct explanation of A
Explanation:
Magnetic poles exist in pairs. So assertion is true. The bar magnet does not exert a torque on itself in its own magnetic field. Torque is proportional to cross product of M and B . The angle between M and B being 0, the cross product is 0. So, there will be no torque. So reason is also true. But R cannot explain A.
Chapter 5 Class 12 Physics MCQ Question 2.
Assertion (A): Magnetic poles cannot be separated by breaking a bar magnet into two pieces.
Reason (R): When a magnet is broken into two pieces, the magnetic moment will be reduced to half.
Answer:
(B) Both A and R are true but R is NOT the correct explanation of A
Explanation: Magnetic poles always exist in pairs even in atomic level. So assertion is true. When a magnet is broken into two pieces, the pole strength remains same; only the length becomes half. So, the magnetic moment becomes half. So, the reason is also true. But R is not the proper explanation of A.
MCQ On Magnetism And Matter Class 12 Question 3.
Assertion (A): The basic difference between magnetic lines of force and electric lines of force is electric lines of force are discontinuous and magnetic lines of force are continuous.
Reason (R): Magnetic lines of force exist in a magnet but no electric lines of force exist in a charged body.
Answer:
(A) Both A and R are true and R is the correct explanation of A.
Explanation:
Let us consider an electric dipole. The electric lines of force exist outside only and not inside the dipole.
Let us take a magnetic dipole. The magnetic lines of force exist outside as well as inside the dipole.
So, it can be said that magnetic lines of force are continuous and electric lines of force are discontinuous.
So assertion and reason both are true and reason explains the assertion too.
Chapter 5 MCQ Class 12 Physics Question 4.
Assertion (A): Gauss theorem is not applicable in magnetism.
Reason (R): Magnetic monopole does not exist.
Answer:
(A) Both A and R are true and R is the correct explanation of A
Explanation:
Gauss’s theorem of magnetism is different from that for electrostatics because electric charges may not exist in pair but magnetic poles always exist in pair. So assertion is true. Magnetic monopole does not exist. Magnetic poles always exist in pair. So reason is also true and reason clearly explains the assertion.
Physics Chapter 5 MCQ Class 12 Question 5.
Assertion (A): A compass needle when placed at Earth’s magnetic pole rotates in vertical plane. Reason (R): The Earth has only horizontal component of its magnetic field at the poles.
Answer:
(D) A is false and R is true
Explanation:
Magnetic needle can rotate in horizontal plane only. But at poles, there is no horizontal component of Earth’s magnetic field.
So, the needle will remain horizontal and will point in any direction. Hence the assertion is false.
At poles, Earth has only vertical components of its magnetic field. Hence, the reason is also false.
Class 12th Physics Chapter 5 MCQ Question 6.
Assertion (A): Compass needle points the magnetic north-south direction.
Reason (R): The magnetic meridian of the earth merges with the axis of rotation of earth.
Answer:
(D) A is false and R is true
Explanation:
Compass needle points the magnetic north-south direction. So the assertion is true. Earth’s magnetic meridian is along its axis through magnetic north-south direction. Earth’s axis of rotation is along its geographic north-south direction. The angle between these two axes is 11.3°. Hence, the reason is also false.
Question 7.
Assertion (A): Ferromagnetic substances become paramagnetic beyond Curie temperature.
Reason (R): Domains are destroyed at high temperature.
Answer:
(A) Both A and R are true and R is the correct explanation of A
Explanation:
From Curie Weiss law,
x = \(\frac{C}{T-T_{C}}\)
As temperature increases beyond Curie temperature, susceptibility decreases and the ferromagnetic substances become paramagnetic. So, the assertion is true. Paramagnetic substance has no magnetic domain. At a very high temperature, the domains of ferromagnetic substance get destroyed and the substance transforms into paramagnetic substance. So, the reason is also true and properly explains the assertion.
Question 8.
Assertion (A): Gauss’s law of magnetism is different from Gauss’s law of electrostatics.
Reason (R): Isolated electric charge can exist but isolated magnetic pole cannot exist.
Answer:
(A) Both A and R are true and R is the correct explanation of A
Explanation:
in electrostatics, Gauss’s law:
= \(\int \overrightarrow{\mathrm{E}} \cdot \overrightarrow{d \mathrm{~A}}=\frac{q}{\varepsilon_{0}}\)
Gauss’s law of magnetism:
\(\int \overrightarrow{\mathrm{B}} \cdot \overrightarrow{d \mathrm{~A}}\) = 0
Gauss’s law of magnetism is different from Gauss’s law of electrostatics. Hence, the assertion is true. Electric charge may or may not exist in pair. But magnetic poles always exist in pair. No magnetic monopole exists. This is the reason why Gauss’s law of magnetism is different from Gauss’s law of electrostatics. So, the reason is also true and explains the assertion.
Case-Based MCQs
Attempt any 4 sub-parts out of 5. Each sub-part carries 1 mark.
I. Read the following text and answer the following questions on the basis of the same:
Earth’s magnetism: Earth’s magnetic field is caused by a dynamo effect. The effect works in the same way as a dynamo light on a bicycle. Magnets in the dynamo start spinning when the bicycle is pedaled, creating an electric current. The electricity is then used to turn on the light. This process also works in reverse.
If you have a rotating electric current, it will create a magnetic field. On Earth, flowing of liquid metal in the outer core of the planet generates electric currents. The rotation of Earth on its axis causes these electric currents to form a magnetic field which extends around the planet. The average magnetic field strength in the Earth’s outer core was measured to be 25 Gauss, 50 times stronger than the magnetic field at the surface. The magnetic field is extremely important for sustaining life on Earth.
Without it, we would be exposed to high amounts of radiation from the Sun and our atmosphere would be free to leak into space. This is likely what happened to the atmosphere on Mars. As Mars doesn’t have flowing liquid metal in its core, it doesn’t produce the same dynamo effect. This left the planet with a very weak magnetic field, allowing for its atmosphere to be stripped away by solar winds, leaving it uninhabitable. Based upon the study of lava flows throughout the world, it has been proposed that the Earth’s magnetic field reverses at an average interval of approximately 300,000 years. However, the last such event occurred some 780,000 years ago.
Question 1.
Which of the followings is the reason for Earth’s magnetism ?
(A) Rotation of electric current
(B) Rotation of Earth
(C) Attraction due to other celestial bodies
(D) Solar flares
Answer:
(A) Rotation of electric current
Explanation:
On Earth, flowing of liquid metal in the outer core of the planet generates electric currents. The rotation of Earth on its axis causes these electric currents to form a magnetic field which extends around the planet.
Question 2.
Electric current in the Earth’s body is generated due to:
(A) movement of charged particle in the atmosphere.
(B) flowing of liquid metal in the outer core.
(C) electric discharges during thunderstorm.
(D) its revolution round the Sun.
Answer:
(A) movement of charged particle in the atmosphere.
Explanation:
On Earth, flowing of liquid metal in the outer core of the planet generates electric currents.
Question 3.
Which planet has no own magnetic field ?
(A) Jupiter
(B) Neptune
(C) Mars
(D) Mercury
Answer:
(C) Mars
Explanation:
As Mars doesn’t have flowing liquid metal in its core, it doesn’t produce dynamo effect. So, it has very weak or almost no magnetic field.
Question 4.
Average magnetic field strength in the Earth’s outer core is:
(A) 5 Gauss
(B) 25 Gauss
(C) 500 Gauss
(D) Cannot be measured
Answer:
(B) 25 Gauss
Explanation:
The average magnetic field strength in the Earth’s outer core was measured to be 25 Gauss.
Question 5.
Which of the following statements is true ?
(A) Earth’s magnetic field is due to electric current induced in the ionosphere.
(B) The average magnetic field strength in the Earth’s outer core is equal to the magnetic field at the surface.
(C) Earth’s magnetic field reverses at an average interval of approximately 3,00,000 years.
(D) Angle of dip is same at every point of the surface of Earth.
Answer:
(C) Earth’s magnetic field reverses at an average interval of approximately 3,00,000 years.
Explanation:
Based upon the study of lava flows throughout the world, it has been proposed that the Earth’s magnetic field reverses at an average interval of approximately 300,000 years.
II. Read the following text and answer the following questions on the basis of the same:
If we move into space and study the Earth’s invisible magnetic field, it wouldn’t really look like a bar magnet at all. Earth’s magnetic field gets stretched out into a comet-like shape with a tail of magnetism that stretches millions of miles behind the earth, opposite to the Sun. The Sun has a wind of gas that pushes the earths field from the left to the right in the picture.
The core of the Earth is an electromagnet. Although the crust is solid, the core of the Earth is surrounded by a mixture of molten iron and nickle. The magnetic field of Earth is caused by currents of electricity that-flow in the molten core. These currents are hundreds of miles wide and flow at thousands of miles per hour as the Earth rotates.
The powerful magnetic field passes out through the core of the Earth, passes through the crust and enters space. This picture shows the solid inner core region (inner circle) surrounded by a molten outer core (the area between the two circles). The currents flow in the outer core, travel outwards through the rest of the earth’s interior. If the Earth rotated faster, it would have a stronger magnetic field.
By the time the field has reached the surface of Earth, it has weakened a lot, but it is still strong enough to keep your compass needles pointed towards one of its poles. All magnets have two poles: a North Pole and a South Pole. The magnetic poles of earth are not fixed on the surface, but wander quite a bit. The pole in the Northern Hemisphere seems to be moving northwards in geographic latitude by about 10 kilometres per year by an average.
Question 1.
Earth’s magnetic field has a:
(A) shape of the magnetic field of a bar magnet.
(B) shape of the magnetic field of a horseshoe magnet.
(C) shape of a sphere.
(D) None of the above
Answer:
(D) None of the above
Explanation:
Earth’s magnetic field gets
stretched out into a comet-like shape with a tail of magnetism that stretches millions of miles < behind the Earth, opposite from the Sun.
Question 2.
Core of the Earth is:
(A) an electromagnet.
(B) a permanent magnet.
(C) a unipolar magnet.
(D) None of these
Answer:
(A) an electromagnet.
Explanation:
The core of the Earth is an electromagnet. Although the crust is solid, the core of the Earth is surrounded by a mixture of molten iron and nickle. The magnetic field of Earth is caused by currents of electricity that flow in the molten core.
Question 3.
The magnetic poles of Earth are:
(A) fixed on the surface
(B) wander throughout the Earth’s surface
(C) wander about 1000 kilometres per year on an average.
(D) wander about 10 kilometres per year on an average.
Answer:
(D) wander about 10 kilometres per year on an average.
Explanation:
The magnetic poles of Earth are not fixed on the surface, but wander quite a bit. The pole in the Northern Hemisphere seems to be moving northwards in geographic latitude by about 10 kms per year on an average.
Question 4.
Earth’s magnetic field may increase if:
(A) it rotates on its axis faster.
(B) its direction of rotation is changed.
(C) it revolves round the Sun faster.
(D) All of the above
Answer:
(A) it rotates on its axis faster.
Explanation:
If the Earth rotated faster, it would have a stronger magnetic field.
Question 5.
The Earth’s magnetism is due to:
(A) induction of Sun’s magnetism.
(B) current produced by the movement of molten metals.
(C) sea current.
(D) revolution of the Earth round the Sun.
Answer:
(B) current produced by the movement of molten metals.
Explanation:
The Earth crust is solid, the core of the Earth is surrounded by a mixture of molten iron and nickle. The magnetic field of Earth is caused by currents of electricity that flow in the molten core. These currents are hundreds of miles wide and flow at thousands of miles per horn as the Earth rotates.
III. Read the following text and answer the following questions on the basis of the same:
Super magnet:
The term super magnet is a broad term and encompasses several families of rare-earth magnets that include seventeen elements in the periodic table; namely scandium, yttrium, and the fifteen lanthanides. These elements can be magnetized, but have Curie temperatures below room temperature. This means that in their pure form, their magnetism only appears at low temperatures. However, when they form compounds with transition metals such as iron, nickel, cobalt, etc. Curie temperature rises well above room temperature and they can be used effectively at higher temperatures as well. The main advantage they have over conventional magnets is that their greater strength allows for smaller, lighter magnets to be used.
Super magnets are of two categories:
(i) Neodymium magnet:
These are made from an alloy of neodymium, iron, and boron. This material is currently the strongest known type of permanent magnet. It is typically used in the construction of head actuators in computer hard drives and has many electronic applications, such as electric motors, appliances, and magnetic resonance imaging (MRI).
(ii) Samarium-cobalt magnet:
These are made from an alloy of samarium and cobalt. This second- strongest type of rare Earth magnet is also used in electronic motors, turbo-machinery, and because of its high temperature range tolerance may also have many applications for space travel, such as cryogenics and heat resistant machinery.
Rare-earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder. Since super magnets are about 10 times stronger than ordinary magnets, safe distance should be maintained otherwise these may damage mechanical watch, CRT monitor, pacemaker, credit cards, magnetically stored media etc.
These types of magnets are hazardous for health also. The greater force exerted by rare-earth magnets creates hazards that are not seen with other types of magnet. Magnets larger than a few centimeters are strong enough to cause injuries to body parts pinched between two magnets or a magnet and a metal surface, even causing broken bones. Neodymium permanent magnets lose their magnetism 5% every 100 years. So, in the truest sense Neodymium magnets may be considered as a permanent magnet.
Question 1.
Curie point of pure rare Earth elements is
(A) very high.
(B) below room temperature.
(C) 0 K.
(D) varies from element to element.
Answer:
(B) below room temperature.
Explanation:
Rare-Earth elements which can be magnetized have Curie temperatures below room temperature. This means that in their pure form, their magnetism only appears at low temperatures.
Question 2.
Neodymium and Samarium are
(A) diamagnetic.
(B) paramagnetic.
(C) ferromagnetic.
(D) not magnetic materials.
Answer:
(C) ferromagnetic.
Question 3.
Super magnets are about time stronger than ordinary magnets.
(A) 10
(B) 100
(C) 1000
(D)10000
Answer:
(A) 10
Question 4.
To raise the Curie point of rare Earth elements.
(A) they are coated with gold.
(B) compounds are formed with transition metals.
(C) they are oxidized.
(D) None of the above
Answer:
(B) compounds are formed with transition metals.
Explanation:
When rare-Earth elements form compounds with transition metals such as iron, nickel, cobalt, etc Curie temperatures thus rise well above room temperature.
Question 5.
Neodymium permanent magnets lose their magnetism % every 100 years.
(A) 50
(B) 0.5
(C) 10
(D) None of the above
Answer:
(B) 0.5
Explanation:
Neodymium permanent magnets lose their magnetism 5% every 100 years. So, in the truest sense. Neodymium magnets may be considered as a permanent magnet.