Assertion (A): To produce high magnetic moment from a current carrying cable, it should be turned in maximum number of circular loops.
Reason (R): Magnetic moment is directly proportional to number of turns of circular loop for a given length of wire.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Magnetic moment is \(M = NIA\). For a fixed wire length \(L\), \(r = L/(2\pi N)\) and \(A = \pi r^2 = L^2/(4\pi N^2)\). So \(M = IL^2/(4\pi N)\). Assertion (A) is false as \(M\) is inversely proportional to \(N\). Reason (R) is false as \(M\) is inversely proportional to \(N\) for a given wire length. Both (A) and (R) are false.
Assertion (A): When a magnet is brought near iron nails, only translatory force act on it.
Reason (R): The field due to a magnet is generally uniform.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A): A magnet attracts iron nails, causing a translatory force. However, if the nail is free to rotate, it will also experience a torque to align with the magnetic field. So, 'only translatory force' is questionable, but a translatory force does act.
Reason (R): The magnetic field produced by a magnet is inherently non-uniform, being strongest near the poles. Therefore, (R) is false. Thus, (A) is true (considering the translatory attraction) but (R) is false.
Assertion (A): Magnetic field arises due to charge in motion but a system may have magnetic moment even though its net charge is zero.
Reason (R): Uncharged magnetic material may have dipole moment.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Magnetic fields are produced by moving charges. Atoms/molecules with electron motion have magnetic moments even if neutral. Uncharged materials like ferromagnets have atomic dipole moments. Reason (R) explains how uncharged materials can have dipole moments, thus supporting Assertion (A).
Assertion (A): The poles of magnet cannot be separated by breaking into two pieces.
Reason (R): The magnetic moment will be reduced to half when a magnet is broken into two equal pieces.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Magnetic monopoles do not exist; breaking a magnet creates two smaller magnets, each with North and South poles, making Assertion (A) true. Breaking a uniform magnet into two equal pieces reduces its magnetic moment (M = ml) by half (as length (l) is halved), making Reason (R) true. Reason (R) describes a quantitative change, not the fundamental reason for non-separation of poles.