The temperature of the black body that radiates heat at a rate of $459.27 \times 10^4 W m^{-2}$ is:

Which one of the following is the characteristic of Planck's quantum theory of radiation?

Pervost's theory of heat exchange is not applicable at temperature

Two spheres made of same material have radii in the ratio 2 : 1. If both the spheres are at same temperature, then what is the ratio of heat radiation energy emitted per second by them?

A temperature of a body is ${400^ \circ }$ C. Assuming the surrounding temperature to be negligible. At what temperature will body emit double energy radiation?

If the temperature of a hot body is increased by $50\%$, then the increase in the quality of emitted heat radiation will be

If the operating voltage of X-ray tube is $50$kV then velocity of X-ray?

The hydrogen atom in its ground state is excited by means of monochromatic radiation of energy $12.75ev$. How many different lines are possible in the resulting spectrum? You may assume the ionization energy for hydrogen atom as $13.6\ eV$

If $c$ is the velocity of electromagnetic radiation $e$ is the charge of an electron $m$ is the mass of an electron and $h$ is the Planck's constant, then the combination of these universal constant that is dimensionless, is

The radiation corresponding to 3 $\rightarrow $ s 2 transition of hydrogen atom falls on a metal surface to produce photoelectrons. These electrons are made to enter a magnetic field of $3 \times 10 ^ { - 4 } T$ . If the radius of the largest circular path followed by these electrons is 100 mm, the work function of the metal is close to 

Two black metallic spheres of radius 4m, at 2000 K and 1m at 4000 K will have ratio of energy radiation as

Two sphere of same material and of same emissivity have radii 1 m and 4 m and temperature 4000 K and 1000 K, respectively. The ratio of radiation emitted per sec is  

We find that the temperature of air decreases as one goes up from the earth's surface because

Choose the correct answer from the alternatives given.
Radiations of intensity $0.5\ W/m^2$ are striking a metal plate. The pressure on the plate is then

A pan filled with hot food cools from $94^oC$ to $86^oC$ in$2$ minutes when the room temperature is at $20^oC$. The time taken to cool it from $71^oC$ to $69^oC$ is 

Five kilomoles of oxygen is heated at constant pressure. The temperature of the oxygen gas is increased from 295 K to 305 K. If the molar heat capacity of oxygen at  constant pressure is 6.994 kcal/kmole K. The amount of heat absorbed is in kcal,

Water is used to cool radiators of engines, because:

Star A emits radiation of maximum intensity at a wavelength of $5000 \mathring{A}$ and it has temperature $ 1227^oC $. If star B has temperature $ 2727^oC $ , then the maximum intensity would be observed at