For a perfectly black body, coefficient of emission is

Two rods of different metals have coefficients of linear expansion '$$\alpha_1$$' and '$$\alpha_2$$' respectvely. Their respective lengths are '$$\mathrm{L}_1$$' and '$$\mathrm{L}_2$$'. At all temperatures ($$\mathrm{L}_2-\mathrm{L}_1$$) is same. The correct relation is

The temperature of a black body is increased by $$50 \%$$, then the percentage increase in the rate of radiation by the body is approximated

A particle excuting S.H.M starts from the mean position. Its amplitude is 'A' and time period '$$\mathrm{T}$$' At what displacement its speed is one-fourth of the maximum speed?