Liquid cools from $50^oC$ to $45^oC$ in $5$ minutes and from $5^oC$ to $41.5^oC$ in the next $5$ minutes. The temperature of the surrounding is......... $^oC$

Two identical conducting rods are first connected independently to two vessels, one containing water at $100^o\ C$ and the other containing ice at $0^o\  C$. In the second case, the rods are joined end to end and connected to the same vessels. Let $q_1$ and $q_2\  g/s$ be the rate of melting of ice in the two cases respectively. The ratio $q_2/q_1$ is

Two rods $A$ and $B$ of same cross-sectional are $A$ and length $l$ connected in series between a source $(T_1 = 100^o C)$ and a sink $(T_2 = 0^o C)$ as shown in figure. The rod is laterally insulated  If $T_A$ and $T_B$ are the temperature drops across the rod $A$ and $B$, then 

Assuming newton's law of cooling to be valid, body at temperature $50^o\ C$ in surrounding of temperature $20^o\ C$ , achieve steady state with help of $100\ W$ heater. If same body has temperature $35^o\ C$ in same surrounding, then power of heater required to maintain steady state  ........ $W$

The power radiated by a black body is $P$ and it radiates maximum energy around the wavelength $\lambda_0$. If the temperature of the black body is now changed so that it radiates maximum energy around wavelength $\frac{3}{4}\lambda_0$, the power radiated by it will increase by a factor of

A black body, at a temperature of $227\,^oC$ radiates heat at a rate of $7\, cal\, cm^{-2} \,s^{-1}$. At a temperature of $727\,^oC$, the rate of heat radiated in the same $units$ will  be ..... $unit$