# Moving Charges and Magnetism MCQ | Class 12 | Physics | Chapter-4

## Moving Charges and Magnetism MCQ Chapter 2

Magnetism is a phenomenon, which arises from the motion of electric charges and produces magnetic fields.

Below are some of the very important NCERT Moving Charges and Magnetism MCQ Class 12 Physics Chapter 4 with answers. These Moving Charges and Magnetism MCQ have been prepared by expert teachers and subject experts based on the latest syllabus and pattern of CBSE Term 1 examination.

We have given Moving Charges and Magnetism MCQ Class 12 Physics Questions with answers to help students understand the concept.

MCQ Questions for Class 12 Physics are very important for the latest CBSE Term 1 and Term 2 pattern. These MCQs are very important for students who want to score high in CBSE Board, NEET and JEE exam.

We have put together these NCERT MCQ Questions of Moving Charges and Magnetism MCQ for Class 12 Physics Chapter 4 with Answers for the practice on a regular basis to score high in exams. Refer to these MCQs Questions with Answers here along with a detailed explanation.

## MCQ

1 . If we double the radius of a coil keeping the current through it unchanged, what happens to the magnetic field on its axis at very very far away points?

1. Halved
2. Doubled
3. Becomes 4 times
4. Remains unchanged

2. An electron and proton enters a magnetic field with equal velocities. Which one of them experiences more force?

1. Proton
2. Electron
3. Both experience same force
4. It cannot be predicted

3. Lorentz Force is

1. the vector sum of electrostatic and magnetic force acting on a moving charged particle
2. the vector sum of gravitational and magnetic force acting on a moving charged particle
3. electrostatic force acting on a charged particle
4. magnetic force acting on a moving charged particle

4. A proton and a deuterium nucleus having certain kinetic energies enter in a uniform magnetic field with the same component of velocity in the direction of the magnetic field. Which of the following is correct?

1. Which particle has greater pitch depends on the fact that which particle has greater component of velocity perpendicular to magnetic field
2. Deuterium nucleus has greater pitch of helical motion
3. Proton has greater pitch of helical motion
4. Both particles have same pitch of helical motion

5. A charged particle moving in a magnetic field experiences a resultant force

1. in the direction perpendicular to both the field and its velocity
2. in the direction of the field
3. in the direction opposite to that of the field
4. none of the above

6. Magnetic field can be produced by

1. a charge at rest
2. a changing electric field
3. a moving charge
4. both 2 and 3

7. Two electrons move parallel to each other with equal speed ‘v’. The ratio of magnetic and electric forces between them is

1. c/v
2. v/c
3. c2/v2
4. v2/c2

8. A charged particle is moving with velocity ‘v’ in a magnetic field of induction B. The force on the particle will be maximum when

1. v and B are at angle of 45 degree
2. v and B are perpendicular
3. v and B are in same direction
4. v and B are at opposite directions

9. A charge of 1 coulomb is moving in a magnetic field of 0.5 Tesla with velocity of 10 m/s force experienced is

1. 0.5 Newton
2. 5 Newton
3. 10 Newton
4. 0 Newton

10. A charged particle moving with velocity ‘v’ in a uniform magnetic field B the magnetic force experienced by the particle is

1. never 0
2. always 0
3. 0 if B and v are parallel
4. 0 if B and v are perpendicular

11. A charged particle of mass M and charge Q travels on a circular path of radius R that is perpendicular to a magnetic field B. At the time taken by the particle to complete one revolution is

1. 2πm / qB
2. 2πqB / m
3. 2πmq / B
4. 2πq2B / m

12. Magnetic field due to a ring having n turns at a distance ‘x’ on its axis is proportional to (r = radius of ring)

1. r / (x2 + r2)
2. nr2 / (x2 + r2)3/2
3. r2 / (x2 + r2)3/2
4. n2r2 / (x2 + r2)3/2

13. Ampere circuital law states that

1. the line integral of magnetic field along the boundary of open surface is equal to μ0 the total current passing near the surface
2. the line integral of magnetic field along the boundary of the open surface is equal to μ0 the total current passing through the surface
3. the surface integral of magnetic field over the open surface is equal to μ0 the total current passing through the surface
4. the surface integral of magnetic field over the open surface is equal to μ0 the total current passing near the surface

14. Magnetic field at any point on the axis of a current element is

1. maximum
2. minimum
3. constant
4. zero

15. Two thin long parallel wires separated by a distance d carry a current of i A in the same direction. They will

1. attract each other with a force of μ0i2 / 2πd
2. attract each other with a force of μ0i2 / 2πd2
3. repel each other with a force of μ0i2 / 2πd
4. repel each other with a force of μ0i2 / 2πd2

16. The magnetic induction at any point due to long straight wire carrying a current is

1. inversely proportional to the distance from wire
2. inversely proportional to the square of the distance from the wire
3. does not depend on distance
4. proportional to the distance from wire

17. A moving coil sensitive galvanometer gives at once much more deflection. To control its speed of deflection.

1. the body of galvanometer should be earthed
2. high resistance should be connected across the terminals
3. a magnet should be placed near the coil
4. a small copper wire should be connected across its terminal

18. If the current is doubled the deflection is also doubled

1. in ohmmeter
2. a tangent galvanometer
3. a moving coil galvanometer
4. both 2 and 3

19. Which one of the following is experienced by a current carrying loop in uniform magnetic direction?

1. Torque only
2. Force only
3. Neither talk not force
4. Both torque and force

20. A galvanometer having a coil resistance of 60 ohms shows full scale deflection when a current of 1 A passes through it. It can be converted into an ammeter to read current upto 5A by

1. putting in series a resistance of 15 ohm
2. putting in parallel resistance of 15 ohm
3. putting in series a resistance of 240 ohm
4. putting in parallel a resistance of 240 ohm

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21. An electron is projected with uniform velocity along the axis of current carrying long solenoid. Which of the following is true?

1. The electron will be accelerated along the axis
2. The electron path will be circular about the axis
3. The electron will experience a force of 45 degree to the axis and hence execute a helical path
4. The electron will continue to move with uniform velocity along the axis of the solenoid

22. The Galvanometer cannot as such be used as an ammeter to measure the value of current in a given circuit. The following reasons are

(I) the Galvanometer gives full scale deflection for a small current

(II) Galvanometer has a large resistance

(III) Galvanometer can give inaccurate values

1. (I) and (III)
2. (I) and (II)
3. (II) and (III)
4. (I), (II) and (III)

23. A current of 1 A is passed through a straight wire of length 2 m. The magnetic field at a point in air at a distance of 3m from either end of wire and lying on the axis of wire will be

1. Zero
2. μ0T / 2π
3. μ0T / 4π
4. μ0T / 8π

24. A current loop of area A, number of turns N is placed in a uniform magnetic induction B. The angle between the plane of slope and B is θ. The torque acting on the loop will be

1. NIABtanθ
2. NIABsinθ
3. NIABcosθ
4. NIAB

25. The strength of the magnetic field at a point R near a long straight current carrying wire is B. the field at a distance R/2 will be

1. 2B
2. 4B
3. B / 2
4. B / 4

26. A solenoid of length 0.6m has a radius of 2 cm and is made of 600 turns. If it carries a current of 4 A, then the magnitude of magnetic field inside the solenoid is

1. 5.024 x 10-3 T
2. 6.024 x 10-3 T
3. 7.024 x 10-3 T
4. 8.024 x 10-3 T

27. Biot-savart law indicates that the moving electron velocity (v) produce a magnetic field B such that

1. B ⟂ v
2. B || v
3. It is along the line joining electron and point of observation
4. It obeys inverse cube law

28. A milli voltmeter of 25 milli volt range is to be converted into an ammeter of 25 A range. The value of required shunt is

1. 0.001Ω
2. 0.01Ω
3. 0.05Ω

29. A galvanometer of resistance 25Ω is shunted by 2.5Ω resistance. The part of the total current that flows through the galvanometer is given as

1. IG/I0 = 3/11
2. IG/I0 = 1/11
3. IG/I0 = 2/11
4. IG/I0 = 4/11

30. A current carrying loop is placed in a uniform magnetic field. The torque acting on it does not depend on

1. Area of loop
2. Number of turns
3. Shape of loop
4. Angle between normal of coil and magnetic field

31. An electron and a proton are moving along the same direction with the same kinetic energy. They enter a uniform magnetic field acting perpendicular to their velocities. The dependence of radius of their path on their masses is

1. r ∝ m
2. r ∝ √m
3. r ∝ 1/m
4. 1 / √m

32. A charged particle after being accelerated through a potential difference V enters in a uniform magnetic field and moves in a circle of radius r. If V is doubled, the radius of the circle will become

1. 2r
2. √2r
3. 4r
4. r / √2r

33. A magnetic field doesn’t exerts any force on

1. Stream of electrons
2. Stream of protons
3. Unmagnetised piece of electron
4. Stationary charge

34. A steady electric current is flowing through a cylinder conductor

1. The electric field at the axis of the conductor is zero
2. The magnetic field at the axis of the conductor is zero
3. The magnetic field in the vicinity of the conductor is zero
4. None of these

35. What is the shape of a magnet in a moving coil galvanometer to make the radial magnetic field?

1. Concave
2. Horse shoe magnet
3. Convex
4. None of the above

36. Which of the following materials is used in making the core of a moving coil galvanometer?

1. Copper
2. Nickel
3. Iron
4. Both 1 and 2

37. The gyromagnetic ratio of an electron in sodium atom is

1. Depending upon the atomic number of the atom
2. Depending upon the shell number of the atom
3. Independent of that orbit it is in
4. Having positive value

38. A tightly wound 90 turn coil of radius 15 cm has a magnetic field 4 x 10-4T at its centre. The current flowing through it is

1. 1.06 A
2. 2.44 A
3. 3.44 A
4. 4.44 A

39. A square frame of side carries i produces a field B at its centre. The same current is passed through a circular coil having the same perimeter as the square. The field at the centre of the circular coil is B’. Find the ratio of (B’/B).

1. π2 / 3√2
2. π2 / 5√2
3. π2 / 7√2
4. π2 / 8√2

40. A charged particle enters into a space and continues to move undeflected then in that space. Which of the following is true for this case?

1. A uniform horizontal electric field and a vertical magnetic field may be present
2. A vertical electric field alone may be present
3. Uniform electric and magnetic fields, both directed vertically downwards, may be present
4. A uniform horizontal magnetic field alone may be present

41. A right angled triangle has one of the angles as 30°. Two magnetic poles are to be kept at the vertices of the triangle. The ratio of the minimum force of interaction to the maximum force of interaction is

1. 1 : 3
2. 1 : 2
3. 1 : 4
4. 1 : √3

42. Two parallel wires carrying current I1 and I2 are separated by distance d. Force per unit length of wire is F. Then

1. F ∝ d
2. F ∝ 1 / d
3. F ∝ d2
4. F ∝ 1 / d2

43. Two free parallel straight wires carrying currents in opposite direction

1. Attract each other
2. Do not affect each other
3. Repel each other
4. Get rotated to be perpendicular to the each other

44. The AC voltage across a resistance can be measured using a

1. Moving magnet galvanometer
2. Moving coil galvanometer
3. Hot wire voltmeter
4. Potentiometer

45. The restoring couple in the moving coil galvanometer is because of

1. magnetic field
2. material of the coil
3. twist produced in the suspension (.)
4. current in the coil

1 . (3) 2. (3) 3. (1) 4. (2) 5. (1) 6. (4) 7. (4) 8. (2) 9. (2) 10. (3) 11. (1) 12. (2) 13. (2) 14. (4) 15. (1) 16. (1) 17. (3) 18. (3) 19. (1) 20. (1) 21. (4) 22. (2) 23. (1) 24. (3) 25. (1) 26. (1) 27. (1) 28. (1) 29. (2) 30. (3) 31. (1) 32. (4) 33. (4) 34. (2) 35. (1) 36. (3) 37. (3) 38. (1) 39. (4) 40. (4) 41. (1) 42. (2) 43. (3) 44. (3) 45. (3)

## Assertion-Reasoning Based MCQ

Code

1. If both assertion and reason are true and reason is the correct explanation of assertion.
2. If both assertion and reason are true, but reason is not the correct explanation of assertion.
3. If the assertion is true, but the reason is false.
4. If the assertion is false, but the reason is true.

1 . Assertion When a test charge moves through the magnetic field, its momentum changes but kinetic energy remains same.

Reason The magnetic force acts as a centripetal force, which is perpendicular to the instantaneous velocity and so does no work.

2. Assertion Magnetic field interacts with a moving charge.

Reason A moving charge produces a magnetic field.

3. Assertion Free electron always keeps on moving in a conductor even then no magnetic force act on them in magnetic field unless a current is passed through it.

Reason The average velocity of free electron is zero.

4. Assertion Two beam of electrons traveling in the same direction repel each other.

Reason The electrostatic interaction is less than the magnetic interaction.

5. Assertion If the current in a solenoid is reversed in direction while keeping the same magnitude, the magnetic field energy stored in the solenoid decreases.

Reason Magnetic field energy density is proportional to square of current.

6. Assertion The magnetic field produced by a current carrying solenoid is independent of its length and cross-sectional area.

Reason The magnetic field inside the solenoid is uniform.

7. Assertion If two long wire, hanging freely an connected to a battery in series, they come closer to each other.

Reason Force of attraction acts between the two wires carrying current.

8. Assertion In a shunted galvanometer only 10% current passes through the galvanometer. The resistance of the galvanometer is G. Then resistance of the shunt in G/9.

Reason If S is the resistance of the shunt, then voltage across S and G is same.

9. Assertion To convert a galvanometer into an ammeter a small resistance is connected in parallel with it.

Reason The small resistance increases the combined resistance of the combination.

10. Assertion An ammeter is always connected in series whereas a voltmeter is connected in parallel.

Reason An ammeter is a low resistance galvanometer while a voltmeter is high resistance galvanometer.

1 . (1)

Kinetic energy of the charged particle remains same in the circular path while velocity and momentum of the particle changes because of continous change in the direction of motion.

2. (1)

A moving charge experience a force in magnetic field. It is because of interaction of two magnetic fields, one which is produced due to the motion of charge and other in which charge is moving.

3. (1)

In the absence of electric field, the free electron in a conductor are in a state of random motion, like molecules in a gas. Their average velocity is zero, i.e, they do not have any net magnetic force on the free electrons in the magnetic field. On passing the current, the free electrons acquire drift velocity in a definite direction, hence magnetic force acts on them, unless the field has no perpendicular component.

4. (3)

Two beams of electron traveling in the same direction repel each other because the electrostatic interaction is more that the magnetic interaction.

5. (4)

Reversing the direction of the current reverses the direction of magnetic field. However, it has no effect on the magnetic field energy density, which is proportional to the square of the magnitude interaction.

6. (2)

The earth’s magnetic field is towards north and the velocity of electron is vertically downward. Applying Fleming’s left hand rule, the direction of force is towards west. Therefore, an electron coming from outer space will be deflected toward west.

7. (4)

When two long parallel wires, are connected to a battery in series. They carry current in opposite directions, hence they repel each other.

8. (2)

IgG = (I-Ig)S

S = (Ig / I – Ig) G

Ig = I / 10

S = G / 9

9. (3)

An ammeter should have a low resistance which we get when we connect low resistance in parallel with galvanometer.

10. (1)

An ammeter is a low resistance device and is connected in series so as the whole circuit current flows through it for an accurate measurement. A voltmeter is a device having a high resistance. So, if we connect it in series, it would hinder the current flow in the circuit hence open circuit results.

## Case Study Based MCQ

1 . A charged particle enters into a uniform magnetic field and follows a circular path as shown. This happens when the particle enters perpendicular to the magnetic field. It gets deflected by magnetic Lorentz force arrows indicate the direction of motion of the charged particle.

If V the velocity of the particle of charge q and B is the magnetic field, then the force acting on the particle is given by: F = q ( v X B )

In the particle velocity is perpendicular to the magnetic field, then the magnetic of the force is F = qvB. This force provides the necessary centripetal force for the particle and the radius of the circular path is given by

r = mv / qB

The direction of deflection also depends on the nature of the charge. If the particle enters the fields at an angle other than 90°, then, the path of the particle will be helical.

(i) Which of the following particles will not get affected if sent into a magnetic field normal to it?

(a) Alpha

(b) Positron

(c) Neutron

(d) Electron

(ii) When a proton and an electron enter a magnetic field normal to it, which of the following statements is correct (Assume that their speeds are equal)?

(a) They will get deflected in opposite directions

(b) Radius of circular path of electron will be less

(c) Radius of circular path of proton will be less

(d) Both (a) and (b)

(iii) A deutron enters a magnetic field parallel to it. Its path inside the field will be

(a) a straight line

(b) circle

(c) helix

(d) parabola

(iv) If a proton, a deuteron and an alpha particle are projected into a magnetic field perpendicular to it with the same speed, which of them will have the path of highest radius?

(a) Proton

(b) Deuteron

(c) Alpha particle

(d) Both (b) and (C)

(v) An electron enters a magnetic field making an angle of 45° with it. The path of the electron will be

(a) Straight line

(b) Circle

(c) Helix

(d) Parabola

2. Biot Savart law was given by Biot and Savart after doing many experiments. This law is related with the magnetic field induced at any point due to a small current carrying element. According to the law, the magnetic field induced at a point near the current carrying element is directly proportional to the current flowing in the conductor, length of the element, sinፀ and inversely proportional to the square of the distance of point from the element.

(i) Biot Savart law was given by

(a) Oersted

(b) Ampere

(c) Biot and Savart

(d) Maxwell

(ii) Biot Savart law is related with the ______ induced at a point near current carrying element.

(a) Magnetic field

(b) Gravitational field

(c) Electric field

(d) None of these

(iii) Induced magnetic field is directly proportional to

(a) i

(b) dl

(c) sinፀ

(d) All of these

(iv) The magnetic field induced at a point is inversely proportional to

(a) r2

(b) r3

(c) 1 / r

(d) 1 / r2

(v) As the distance between the point and current carrying element decreases, dB

(a) increases

(b) decreases

(c) remains same

(d) both (a) and (b)

3. In certain polar regions of splendid display of colours is seen in the sky. The appearance of dancing green pink light is fascinating and equally puzzling.

Consider a charged particle for mass M and charge Q enters a region of magnetic field B with an initial velocity V. Let this velocity have a component Vp parallel to the magnetic field and a component Vn normal to it. There is no force on a charged particle in the direction of field. Hence the particle continue to travel with the velocity Vp parallel to the field.

The normal component Vn of the particle results in a Lorentz Force which is perpendicular to both and the particle does has a tendency to perform a circular motion in a plane perpendicular to the magnetic field. When this is coupled with the velocity parallel to the field, the resulting trajectory will be a helix along the magnetic field line. Even if the field line bends, the helically moving particle is trapped and guided to move around the field line.

Since the Lorentz Force is normal to the velocity of each point, the field does not work on the particle and the magnitude of the velocity remains the same. During a solar flare, a large number of electrons and protons are rejected from the sun. Some of the get trapped in the Earth’s magnetic field and move in a helical path along the field line.

The field lines come closer to each other near the magnetic poles. Hence, the density of charges increases near the poles. These particles collide with atoms and molecules of the atmosphere. Excited oxygen atoms emit green light an excited nitrogen atoms emit pink light. This phenomenon is called Aurora Borealis in physical science.

(i) Which of the following defines the exact meaning of magnetic field?

(a) Magnetic field is a scalar field that describes the magnetic influence on moving electric charges, electric currents and magnetic materials.

(b) Magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

(c) Both scalar and vector fields that describe the magnetic influence on moving electric charges, electric currents, and magnetic materials.

(d) Magnetic field is a vector field that describes the magnetic influence on static electric charges, electric currents, and magnetic materials.

(ii) Which of the following defines the exact meaning of Lorentz Force the Lorentz force?

(a) The Lorentz force is the combination of electric and magnetic field force on a point charge due to electromagnetic fields

(b) the Lorentz Force is a combination of electric and magnetic force on a point charge due to gravitational field

(c) the Lorentz Force is a combination of gravitational force and magnetic force on a point charge due to electromagnetic field

(d) the Lorentz Force is the combination of electric and centripetal force on the point charge due to electromagnetic fields

(iii) Which of the following defines the exact meaning of circular motion?

(a) Circular motion is apparent outward force on mass with when it is rotated

(b) Circular motion vector field that describes the magnetic influence on moving electric charges electric currents, and magnetic materials

(c) Circular motion in an object is the rate of change of its position with respect to a frame of reference, and is a function of time

(d) Circular motion is a movement of an object along the circumference of a circle or rotation along a circular path

(iv) What does Aurora Borealis mean?

(a) The Aurora Borealis otherwise known as northern lights, is a physics phenomenon that can be magical to observe, striking onlookers to wonder about the cause of the whimsical light that dance overhead.

(b) The Aurora Borealis otherwise known as southern lights, is a physics phenomenon that can be magical to observe, striking onlookers to wander about the cause of the whimsical life that downs overhead

(c) The Aurora Borealis otherwise known as the Eastern lights, is a physics phenomenon that can be magical to observe, striking onlookers to wander about the cause of the whimsical lies that dance overhead

(d) The Aurora Borealis is a apparent outward force on the mass when it is rotated

(v) Consider a tightly wound 100 turn coil of radius 10cm carrying a current of 1A. What is the magnitude of magnetic field at the centre of the coil?

(a) 2.28 x 10-4 T

(b) 6.28 x 10-4 T

(c) 3.28 x 10-4 T

(d) 5.28 x 10-4 T

### Case Study Based MCQ Answers

1 . (i) (c) Neutron particles are not affected by magnetic field.

(ii) (d) Opposite deflection because of opposite charge. Lighter particles get deflected more.

(iii) (a) Straight line

(iv) (d) r is proportional to m/q

(v) (c) Helix

2. (i) (c) Biot and Savart

(ii) (a) Magnetic field

(iii) (d) All of these

(iv) (a) r2

(v) (a) Increase, dB is inversely proportional to r2

3. (i) (b) The exact meaning of magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

(ii) (a) The Lorentz force is the combination of electron and magnetic force on a point charge due to electromagnetic fields. A particle of charge q moving with a velocity v in an electric field E and a magnetic field B experiences a force of F = qE + qvB.

(iii) (d) Circular motion is a movement of an object along the circumstances of a circle or rotation along a circular path. It can be uniform, with constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a 3-D body involves circular motion of its parts.

(iv) (a) The Aurora Borealis otherwise known as northern lights, is a physics phenomenon that can be magical to observe, striking onlookers to wonder about the cause of the whimsical light that dance overhead. This extraordinary display is caused by charged particles being expelled into space from the sun.

(v) (b) B = μ0NI / 2R = (4π x 10-7 x 102 x 1) / (2 x 10-1) = 2π x 10-4 = 6.28 x 10-4 T

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Final Words

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