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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