A sheet is placed on a horizontal surface in front of a strong magnetic pole. A force is needed to :
A. hold the sheet there if it is magnetic.
B. hold the sheet there if it is non-magnetic.
C. move the sheet away from the pole with uniform velocity if it is conducting.
D. move the sheet away from the pole with uniform velocity if it is both, non-conducting and non-polar.
Choose the correct statement(s) from the options given below:
Answer: (D) A and C only
A: A magnetic sheet is attracted by the pole, so a force is needed to hold it in place. True.
B: A non-magnetic sheet feels no magnetic force, so no force is needed to hold it. False.
C: Moving a conducting sheet through the non-uniform field of the pole changes the flux through it and induces eddy currents. By Lenz's law these oppose the motion, so a force is needed even at uniform velocity. True.
D: A non-conducting, non-polar (non-magnetic) sheet has no eddy currents and no magnetic force, so no force is needed for uniform velocity. False.
A and C only.
Solution by Sreeraj P, M.Sc Physics