CBSE Class 12 Physics 2024: question 4
Set in the CBSE Class 12 board exam of 2024, paper 55/1/1, section A, question 4, for 1 mark. Try it first; the hints and our step-by-step solution are below.
Q4 · 1 mark · MCQMoving Charges and Magnetism
A loop carrying a current I clockwise is placed in x – y plane, in a uniform magnetic field directed along z-axis. The tendency of the loop will be to :
- (A)move along x-axis
- (B)move along y-axis
- (C)shrink
- (D)expand
Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/1/1.
Hints
Open one hint at a time and try again before the next.
Hint 1
Find the direction of on one element of the loop.
Hint 2
In a uniform field the net force on a closed loop is zero, so only the radial effect remains.
Step-by-step solution
Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.
A clockwise current in the x–y plane, seen from +z, has magnetic moment along −z. Taking the field along +z, the force on each element points towards the centre of the loop.
- 1 mark
The net force is zero, so the loop does not move. The inward forces tend to make the loop shrink. Option (C).
Answer: Shrink, option (C)
Where the marks are
- Shows the force on each element is radially inward, so the loop shrinks (1 mark)
Revise the chapter
- Chapter: Moving Charges and Magnetism (notes, formulas, where marks are lost and every past question)
- Topic: Torque on a Current Loop and Magnetic Dipole
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