A substance of mass M kg requires a power input of P wants to remain in the molten state at its melting point. When the power source is turned off, the sample completely solidifies in time t seconds. The latent heat of fussion of the substance is …….

Explanation

Since P jouls per second of heat is supplied to keep the
substance in molten state, it means that the substance in
the molten state at its melting point release P jouls of heat
in one second.

The power is turned off then the heat input becomes zero.
But heat output continues. It takes t seconds for the
substance to solidify (given). Therefore total heat released
in `t seconds=Pxxt=mL_(fusion)`
`L_(fusion)=(Pxxt)/m`