Two stars emit maximum radiation of wavelength $3600\,\mathop A\limits^o $  and $4800\,\mathop A\limits^o $  respectively. The ratio of their temperatures is

The radiant energy from sun incident normally at the surface of earth is $20\, k\,cal/m^2- min$. What would have been the radiant energy incident normally on the earth if the sun had a temp. twice of the present one ? ........... $k\,cal/m^2- min$

The temperature of the two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity $K$ and $2K$ and thickness $x$ and $4x$, respectively are $T_2$ and $T_1(T_2 > T_1)$. The rate of heat transfer through the slab, in a steady state is $\left( {\frac{{A\left( {{T_2} - {T_1}} \right)K}}{x}} \right)f$, with $f$ equals to

The wavelength of maximum energy released during an atomic explosion was $2.93\times10^{-10}\, m$. The maximum temperature attained must be, (Weins constant $= 2.93\times10^{-3}\, mK$)

The maximum energy in the thermal radiation from a hot source occurs at a wavelength of $11 \times 10^{-5}\, cm$ . According to Wien's law, the temperature of the source (on kelvin scale) will be $n$ times the temperature of another source (on Kelvin scale) for which the wavelength at maximum energy is $5.5 \times 10^{-5}\, cm$ . The value of $n$ is

A body cools in a surrounding which is at a constant temperature of $\theta _0$ . Assuming that it obeys Newton's law of cooling, its temperature $\theta $ is plotted against time $t$ . Tangents are drawn to the curve at the points $A(\theta  = \theta _1)$ and $B(\theta = \theta _2)$ . These tangents meet the time-axis at angles $\alpha _1$ and $\alpha _2$ as shown in the graph then