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:
- AB and D only
- BA and C only
- CA, C and D only
- DC only
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Correct answer: B
To understand which statement(s) is/are correct, we must explore the interactions between the magnetic field and different types of materials (magnetic, non-magnetic, conducting, non-conducting).
Statement A: If a sheet is magnetic and placed near a strong magnetic pole, it will experience a magnetic force due to the magnetic field. This force could either attract or repel the sheet depending on the polarity of the magnetic pole and the induced or inherent poles in the sheet. A force is needed to hold the sheet stationary against this magnetic force. Hence, statement A is true.
Statement B: If the sheet is non-magnetic, it will not experience any magnetic force because non-magnetic materials do not respond to magnetic fields in a manner where a force would be exerted on them. Thus, no external force is needed to hold a non-magnetic sheet in place near a magnetic pole. Statement B is false.
Statement C: If the sheet is conducting and you move it away from the magnetic pole, it will experience a change in the magnetic flux through it. According to Faraday's Law of Electromagnetic Induction, a change in magnetic flux induces an electromotive force (EMF) and consequently, currents known as eddy currents in the conductor. These induced currents produce their own magnetic fields, which interact with the original magnetic field, leading to a force (Lenz's Law). To move the sheet away with uniform velocity, a force must counteract this magnetic interaction. Therefore, statement C is true.
Statement D: If the sheet is non-conducting and non-polar, it will neither induce currents (since it's non-conducting) nor experience magnetic forces (since it's non-magnetic). Thus, moving such a sheet away from a magnetic pole with uniform velocity does not require overcoming any electromagnetic forces. Statement D is false.
Given these explanations, the correct statements are A and C only.
The correct choice is: Option B: A and C only.
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