Q. 124.5( 2 Votes )

Photons absorbed in matter are converted to heat. A source emitting n photon/sec of frequency v is used to convert 1kg of ice at 0°C to water at 0°C. Then, the time T taken for the conversion
A. decreases with increasing n, with v fixed.

B. decreases with n fixed, v increasing

C. remains constant with n and v changing such that nv = constant.

D. increases when the product nv increases.

Answer :

Energy used to convert ice to water


E = mass × latent heat = mL


Energy absorbed by n photons with frequency v in time T is given by,



This energy is used to convert ice to water,




T α n-1, when v is constant


Hence, time decreases with increasing n, with v fixed.


T α v-1, when n is constant


Hence, time decreases with increasing v, with n fixed.


T α (nv)-1


Hence, time remains constant with n and v changing such that nv = constant.

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