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
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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): Permeability of a ferromagnetic material is independent of the applied magnetic field.
Reason (R): Permeability of ferromagnetic substances is lower for higher value of applied field.
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
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Permeability \(\mu\) of ferromagnetic materials is highly dependent on the applied field and exhibits hysteresis, making Assertion (A) false. While permeability decreases at very high fields due to saturation, it initially increases. So, Reason (R) is not universally true. Therefore, both Assertion (A) and Reason (R) are false.
Assertion (A): A system displaying a hysteresis loop, such as a ferromagnet is a device for storing memory.
Reason (R): A ferromagnetic substance remains magnetised even after external field is removed.
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
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Hysteresis means a material retains magnetization (retentivity) when the external field is removed. This residual magnetism allows the material to 'remember' its magnetic state, forming the basis of magnetic memory. Thus, Reason (R) correctly explains Assertion (A).
Assertion (A): The product of magnetic susceptibility and absolute temperature of a paramagnetic substance is a constant.
Reason (R): Paramagnetic substances obey Curie’s law.
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
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Curie's law states that for paramagnetic substances, magnetic susceptibility (chi) is inversely proportional to absolute temperature (T), i.e., (chi = C/T). This implies (chi T = C), a constant. So Reason (R) directly explains Assertion (A).
Assertion (A): The permanent magnetic moment of the atoms of a material is zero. The material must be diamagnetic.
Reason (R): Hard magnetic materials have high retentivity, high coercivity and large hysteresis- loss and are suitable for permanent magnetism.
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
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Diamagnetic materials are characterized by the absence of permanent atomic magnetic moments, making Assertion (A) true. Hard magnetic materials need high retentivity and coercivity for permanent magnetism, making Reason (R) true. However, the two statements describe different properties and are not causally related.
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
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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.
Assertion (A): All magnetic materials lose their magnetic properties when strongly heated.
Reason (R): Most of the substances show diamagnetism.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
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Ferromagnetic and paramagnetic materials indeed lose their specific magnetic properties upon strong heating (e.g., ferromagnets become paramagnetic above Curie temperature). So, Assertion (A) is true. However, Reason (R) is false; while diamagnetism is a universal property, most substances exhibit paramagnetism (due to unpaired electrons) or ferromagnetism, which mask diamagnetism.
Assertion (A): A paramagnetic sample shows greater degree of magnetisation when cooled.
Reason (R): Magnetisation of paramagnetic material is inversely proportional to temperature.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
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According to Curie's Law, the magnetic susceptibility \(\chi\) of a paramagnetic material is inversely proportional to its absolute temperature \(T\) (i.e., \(\chi \propto \frac{1}{T})\). Thus, cooling (decreasing \(T\)) increases magnetisation. Both assertion and reason are true, and the reason correctly explains the assertion.
Assertion (A): Ferromagnetic materials of high retentivity are used to form permanent magnet.
Reason (R): Ferromagnetic materials have positive intensity of magnetisation.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
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For a permanent magnet, the material must have high retentivity and high coercivity to retain magnetism. Ferromagnetic materials do exhibit positive intensity of magnetisation, which is true, but this general property is not the direct reason for choosing high retentivity for permanent magnets. Both A and R are true, but R is not the correct explanation of A.
Assertion (A): For a perfectly diamagnetic substance, permeability is always 1.
Reason (R): Small pieces of any magnetic substance are attracted by a strong magnetic field.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
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For a perfectly diamagnetic substance (e.g., superconductor), its relative magnetic permeability \(mu_r\) is 0, not 1. Diamagnetic substances are weakly repelled by magnetic fields, not attracted. Therefore, both Assertion (A) and Reason (R) are false.