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.
Assertion (A): The properties of paramagnetic and ferromagnetic substances are not affected by heating.
Reason (R): As temperature changes, the alignment of molecular magnets does not change.
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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The magnetic properties of paramagnetic and ferromagnetic substances are strongly affected by temperature. Paramagnetic susceptibility is temperature-dependent (Curie's Law), and ferromagnets become paramagnets above their Curie temperature. Thermal agitation due to heating disorients molecular magnets. Both Assertion (A) and Reason (R) are false.
Assertion (A): Soft iron is used as transformer core.
Reason (R): Soft iron has narrow hysteresis loop.
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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Soft iron is preferred for transformer cores because its narrow hysteresis loop indicates low energy loss (heat) during repeated cycles of magnetisation and demagnetisation. This property is crucial for efficient transformer operation. Both Assertion and Reason are true, and Reason is the correct explanation of the Assertion.
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.