If Young’s modulus of elasticity is $Y = \dfrac{2mg l^2}{5b t e}$, where ‘g’ is the acceleration due to gravity, ‘m’ is the mass, ‘l’ is the length, ‘b’ is the breadth, ‘t’ is the thickness and ‘e’ is the elongation, then the value of $k$ is
A 567 W bulb has a tungsten filament of length 40 cm and radius $\dfrac{2}{\pi}$ mm. If the radiation of the filament is 81% of that of a perfect black body, then the temperature of the filament is(Stefan's constant, $\sigma = 5.67 \times 10^{-8}$ W m$^{-2}$ K$^{-4}$)