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

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.