Moving Charges And Magnetism

Moving Charges and Magnetism Class 12 Physics MCQs

1. A charged particle is moving in a cyclotron, what effect on the radius of path of this charged particle will occur when the frequency of the ratio frequency field is doubled?
(a) It will also be doubled.
(b) It will be halved.
(c) It will be increased by four times.
(d) It will remain unchanged.

2. Which of the following is not correct about cyclotron?
(a) It is a machine to accelerate charged particles or ions to high energies.
(b) Cyclotron uses both electric and magnetic fields in combination to increase the energy of charged particles.
(c) The operation of the cyclotron is based on the fact that the time for one revolution of an ion is independent of its speed or radius of its orbit.
(d) The charged particles and ions in cyclotron can move on any arbitrary path.

3. If an electron is moving with velocity \(\vec{ν}\) produces a magnetic field \(\vec{B}\), then
(a) the direction of field \(\vec{B}\) will be same as the direction of velocity \(\vec{ν}\) .
(b) the direction of field \(\vec{B}\) will be opposite to the direction of velocity \(\vec{ν}\) .
(c) the direction of field \(\vec{B}\) will be perpendicular to the direction of velocity \(\vec{ν}\) .
(d) the direction of field \(\vec{B}\) does not depend upon the direction of velocity \(\vec{ν}\) .

4. Current flows through uniform, square frames as shown in the figure. In which case is the magnetic field at the centre of the frame not zero?

5. Ampere’s circuital law is given by

6. Two identical current carrying coaxial loops, carry current I in opposite sense. A simple amperian loop passes through both of them once. Calling the loop as C, then which statement is correct?

(c) there may be a point on C where B and dl are
parallel.
(d) none of these

7. The correct plot of the magnitude of magnetic field \(\vec{B}\) vs distance r from centre of the wire is, if the radius of wire is R

8. The nature of parallel and anti-parallel currents are
(a) parallel currents repel and antiparallel cur¬rents attract.
(b) parallel currents attract and antiparallel cur-rents repel.
(c) both currents attract. ’
(d) both currents repel.

9. The magnetic moment of a current I carrying circular coil of radius r and number of turns N varies as
(a) \(\frac{1}{r²}\)
(b) \(\frac{1}{r}\)
(c) r
(d) r²

10. A short bar magnet has a magnetic moment of 0. 65 J T^-1, then the magnitude and direction of the magnetic field produced by the magnet at a distance 8 cm from the centre of magnet on the axis is
(a) 2.5 × 10^-4 T, along NS direction
(b) 2.5 × 10^-4 T along SN direction
(c) 4.5 × 10^-4 T, along NS direction
(d) 4.5 × 10^-4 T, along SN direction

11. A current carrying loop is placed in a uniform magnetic field. The torqe acting on it does not depend upon
(a) area of loop
(b) value of current
(c) magnetic field
(d) None of these

12. In a moving coil galvanometer the deflection (Φ) on the scale by a pointer attached to the spring is

13. A moving coil galvanometer can be converted into an ammeter by
(a) introducing a shunt resistance of large value in series.
(b) introducing a shunt resistance of small value in parallel.
(c) introducing a resistance of small value in series.
(d) introducing a resistance of large value in parallel.

14. The conversion of a moving coil galvanometer into a voltmeter is done by
(a) introducing a resistance of large value in series.
(b) introducing a resistance of small value in parallel.
(c) introducing a resistance of large value in parallel.
(d) introducing a resistance of small value in series.

15. When a magnetic compass needle is carried nearby to a straight wire carrying current, then
(I) the straight wire cause a noticeable deflection in the compass needle.
(II) the alignment of the needle is tangential to an imaginary circle with straight wire as its centre and has a plane perpendicular to the wire
(a) (I) is correct
(b) (II) is correct
(c) both (I) and (II) are correct
(d) neither (I) nor (II) is correct

16. A strong magnetic field is applied on a stationary electron. Then the electron
(a) moves in the direction of the field.
(b) remained stationary.
(c) moves perpendicular to the direction of the field.
(d) moves opposite to the direction of the field.

17. In an inertial frame of reference, the magnetic force on a moving charged particle is \(\vec{F}\) Its value in another inertial frame of reference will be
(a) remained same
(b) changed due to change in the amount of charge
(c) changed due to change in velocity of charged particle
(d) changed due to change in field direction

18. Which one of the following is correct statement about magnetic forces?
(a) Magnetic forces always obey Newton’s third law.
(b) Magnetic forces do not obey Newton’s third law.
(c) For very high current, magnetic forces obey Newton’s third law.
(d) Inside low magnetic field, magnetic forces obey Newton’s third law.

19. A charged particle is moving on circular path with velocity v in a uniform magnetic field B, if the velocity of the charged particle is doubled and strength of magnetic field is halved, then radius becomes
(a) 8 times
(b) 4 times
(c) 2 times
(d) 16 times

20. Two a-particles have the ratio of their velocities as 3 : 2 on entering the field. If they move in different circular paths, then the ratio of the radii of their paths is
(a) 2 : 3
(b) 3 : 2
(c) 9 : 4
(d) 4 : 9

Question 21.
The current sensitibility of a moving coil galanometer increases with decrease in:
(a) magnetic field
(b) area of a coil
(c) number of turns
(d) None of these

Question 22.
A current carring coil is placed in a uniform magnetic field. If the coil turns through an angle θ, then the torque is directly proportional to:
(a) sin θ
(b) cos θ
(c) cot θ
(d) tan θ

Question 23.
The sensitivity of a tangent galvanometer can be increased by increasing:
(a) the radius of the coil
(b) the external magnetic field
(c) the number of turns of the coil
(d) all the above

Question 24.
The permeability of a paramagnetic substance is:
(a) very large
(b) small but more than unity
(c) less than unity
(d) negative

Question 25.
Which of the following shows that the earth behaves as a magnet?
(a) Repulsion between like poles .
(b) Attraction between unlike poles
(c) Null points in the magnetic field of a bar magnet
(d) No existence of isolated magnetic poles

Question 26.
What is the angle of dip at the magnetic poles ?
(a) 30°
(b) 0°
(c) 45°
(d) None of these

Question 27.
A charged particle of mass m and charge q travels on a circular path of radius r i.e., perpendicular to the magnetic field B. The time taken by particle to complete on revolution is :
(a) \(\frac{2πqB}{m}\)
(b) \(\frac{2πm}{qB}\)
(c) \(\frac{2πmq}{B}\)
(d) \(\frac{2πq^2B}{m}\)

Question 28.
Circular loop of radius 0.0157 m carries a current 2 A. The magnetic field at the centre of the loop is :
(a) 1.57 × 10^-3Wb/m²
(b) 8.0 × 10^-5 Wb/m²
(c) 2.0 × 10^-3 Wb/m²
(d) 3.l4 × 10^-1 Wb/m²

Question 29.
What happens to the magnetic field at the centre of a circular current carrying coil if we double the radius of the coil keeping the current unchanged?
(a) halved
(b) doubled
(c) quadrupled
(d) remains unchanged

Question 30.
When we double the radius of a coil keeping the current through it unchanged, what happens to the magnetic field directed along its axis at far off points?
(a) halved
(b) doubled
(c) quadrupled
(d) remains unchanged

Question 31.
The strength of the magnetic field around an infinite current carrying conductor is :
(a) same everywhere
(b) inversely proportional to the distance
(c) directly proportional to the distance
(d) None of these

Question 32.
A current carrying power line carries current from west to east. Then the direction of the magnetic field 2 m above it is :
(a) west to east
(b) south to north
(c) north to south
(d) None of these

Question 33.
According to Ampere’s Circuital law

Question 34.
The force between two parallel current carrying conductors is F. If the current in each conductor is doubled, then the force between them becomes :
(a) 4F
(b) 2F
(c) F
(d) \(\frac{F}{4}\)

Question 35.
How much force will be experienced by a moving charge in a magnetic field? The symbols have their usual meanings.
(a) \(\vec{F}\) = q(\(\vec{v}\).\(\vec{B}\))
(b) \(\vec{F}\) = \(\frac{q}{(\vec{v}.\vec{B})}\)
(c) \(\vec{F}\) = \(\frac{q}{2}\)\((\vec{v}×\vec{B}\))
(d) \(\vec{F}\) = q(\(\vec{v}\)×\(\vec{B}\))

Question 36.
Which of the following is not a unit of magnetic induction?
(a) gauss
(b) tesla
(c) oersted
(d) weber/metre²

Question 37.
The magnetic field produced by an / meter long straight (x cry thin) current (I) carry ing conductor at any point on itself is :
(a) zero
(b) infinite
(c) \(\frac{µ_0l}{4πl}\)
(d) \(\frac{µ_0l}{2πl}\)

Question 38.
A charge + q is sent through a magnetic field. The force acting on it is maximum w hen the angle between the direction of motion of the charged particle and the magnetic field :
(a) 0°
(b) 45°
(c) 90°
(d) 180°

Question 39.
An electron having mass ‘m’ and Kinetic energy E enters in uniform magnetic field B perpendicular, then its frequency will be:
(a) \(\frac{eE}{qmB}\)
(b) \(\frac{2πm}{eB}\)
(c) \(\frac{eB}{2πm}\)
(d) \(\frac{2m}{eBE}\)

Question 40.
A wire of length 2 metre carries a current 1 ampere, is bent to form a circle. The magnetic moment of the coil is :
(a) 2π
(b) π/2
(c) π/4
(d) 1/π

Question 41.
The magnetic field of a given length of a ware for single turn coil at its centre is B. Then.its value for two turns of coil will be :
(a) B/4
(b) B/2
(c) 4B
(d) 2B

Question 42.
When charged particle enters-a uniform magnetic field, its K.E.:
(a) remains constant
(b) increases
(c) decreases
(d) becomes zero

Question 43.
To convert galvanometer into voltmeter one should connect :
(a) high resistance in series with galvanometer
(b) low resistance in series with galvanometer
(c) high resistance in parallel with galvanometer
(d) low resistance in parallel with galvanometer

Question 44.
A charge q moves in a region, where electric field E and magnetic field B both exist, then force on it is :
(a) \(\vec{F}\) = q(\(\vec{v}\)×\(\vec{B}\))
(b) \(\vec{F}\) = q{\(\vec{E}\)×(\(\vec{v}\) × \(\vec{B}\))}
(c) \(\vec{F}\) = q(\(\vec{E}\) + (\(\vec{B}\) × \(\vec{v}\))
(d) \(\vec{F}\) = q(\(\vec{B}\) + (\(\vec{E}\) ×\(\vec{v}\))

Question 45.
Isoclinic lines are the lines joining places with :
(a) equal dip
(b) equal declination
(cj equal dip and declination
(d) None of these

Question 46.
Two identical bar magnets each of dipole moment p and length I are perpendicular to each other as shown in Fig. The dipole moment of the combination is:

(a) √2 p
(b) \(\frac{p}{√2}\)
(c) P
(d) 2p

Question 47.
The most suitable metal for making permanent magnets is :
(a) iron
(b) steel
(c) copper
(d) aluminium

Question 48.
The SI unit of magnetic dipole moment is’
(a) Ampere
(b) Ampere metre²
(c) Tesla
(d) None of these

Question 49.
Earth’s magnetism was discovered by:
(a) Gauss
(b) Oersted
(c) Ampere
(d) Gilbert

Question 50.
According to Gauss’s theorem in magnetism, surface integral of magnetic field intensity over a surface (closed or open) is always:
(a) -1
(b) 1
(c) 0
(d) infinity

Question 51.
Tesla is a unit of:
(a) electric flux
(b) magnetic flux
(c) magnetic field
(d) electric field

Question 52.
10 eV electron is circulating in a plane at right angle to a uniform field of magnetic induction 10^-1 Wb/m² (1G). The orbital radius of electron is:
(a) 12 cm
(b) 16 cm
(c) 11 cm
(d) 18 cm

Question 53.
A cyclotron can be used to produce high energy:
(a) neutrons
(b) deutrons
(c) β particles
(d) α partifcles

Question 54.
The radius of the trajectory of a charged particle in a uniform magnetic field is proportional to the:
(a) charge on the particle
(b) energy of the particle
(c) momentum of the particle
(d) all the above

Question 55.
The force \(\vec{F}\) experienced by a particle of charge q moving with velocity \(\vec{v}\) in a magnetic field \(\vec{B}\) is given by,
(a) \(\vec{F}\) = q(\(\vec{F}\) × \(\vec{B}\))
(b) \(\vec{F}\) = q(\(\vec{B}\) × (\(\vec{b}\))
(c) \(\vec{F}\) = q(\(\vec{v}\) × (\(\vec{B}\))
(d) \(\vec{F}\) = q(\(\vec{v}\) × \(\vec{B}\))

Question 56.
The torque acting on a magnetic dipole of moment \(\vec{p_m}\) when placed in a magnetic field \(\vec{B}\) is:
(a) p_mB
(b) \(\vec{p_m}\) × \(\vec{B}\)
(c) \(\vec{p_m}\)\(\vec{B}\)
(d) \(\frac{p_m}{B}\)

Question 57.
In thomson spectrograph \(\vec{E}\) ⊥ \(\vec{B}\), then velocity of electron beam will be:
(a) |\(\vec{E}\)|/|\(\vec{B}\)|
(b) \(\vec{E}\) × \(\vec{B}\)
(c) |\(\vec{B}\)|/|\(\vec{E}\)|
(d) E² / B²