Given below are two statements. One is labelled as Assertion (A) and the other is labelled as reason (R).
Assertion: Thermal expansion of solids is due to the anharmonicity of the lattice vibrations.
Reason: As the temperature of the solid increases, the amplitude of vibrating atoms increases.
In the light of the given statements, choose the correct answer from the options given.

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Both (A) and (R) are true but (R) is not the correct explanation of (A)

Both (A) and (R) are true and (R) is the correct explanation of (A)

Both (A) and (R) are false

(A) is true but (R) is false

answer is B.

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Detailed Solution

The thermal expansion of a material is related to the anharmonicity of the interatomic potential of its constituent atoms. Increasing the temperature of the sample increases the vibrational energy of the atoms. Hence A is true.

Higher the temperature, higher is the thermal energy of each molecule and thus greater is the amplitude of the vibrations. Therefore, when we heat the solid, its temperature increases, which increases the thermal energy of the molecules. As a result, the amplitude of vibrations increases. Hence R is true.

Both A and R are true. But R does not explain A.

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