Moving Charges and Magnetism Class 12 Physics MCQs Pdf
25. 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
Answer
Answer: c
26. 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.
Answer
Answer: b
27. 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
Answer
Answer: c
28. 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.
Answer
Answer: b
29. 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
Answer
Answer: b
30. 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
Answer
Answer: b
31. 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.
Answer
Answer: d
32. 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.
Answer
Answer: d
33. 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 \(\vec{ν}\) .
Answer
Answer: c
34. 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?
Answer
Answer: c
35. Ampere’s circuital law is given by
Answer
Answer: b
36. 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
Answer
Answer: b