A black body is at 727^o C. It emits energy at a rate which is proportional to:

• (727)²

• (1000)⁴

• (1000)²

• (1000)²

An engine has an efficiency of 1/6. When the temperature of sink is reduced by 62^o C, its efficiency is doubled. The temperature of the source is:

• 124^o C

• 37^o C

• 62^o C

• 62^o C

A black body at 1227°C emits radiations with maximum intensity at a wavelength of 5000 Å. If the temperature of the body is increased by 1000°C, the maximum intensity will be observed at

• 4000 Å

• 5000 Å

• 6000 Å

• 6000 Å

A gas mixture consists of 2 moles of O₂ and 4 moles of Ar at temperature T. Neglecting all vibrational modes, the total internal energy of the system is

• 4 RT

• 15 RT

• 9 RT

• 9 RT

The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature T (Kelvin) and mass m, is

A spherical black body with a radius of 12 cm radiates 450-watt power at 500 K. If the radius were halved and the temperature doubled, the power
radiated in watt would be

• 225

• 450

• 1800

• 1800

107.

The power radiated by a black body is P and it radiates maximum energy at wavelength, λ₀. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength $\frac{3}{4}{\lambda }_0$, the power radiated by it becomes nP. The value of n is

• 3/4

• 4/3

• 81/256

• 256/81

At what temperature will the rms speed of oxygen molecules become just sufficient for escaping from the Earth's atmosphere?

(Given: Mass of oxygen molecule (m) = 2.76 x 10^-26 kg
Boltzmann's constant k_B = 1.38 x 10^-23 JK^-1)

• 2.508 × 10⁴ K

• 8.360 × 10⁴ K

• 1.254 × 10⁴ K

• 5.016 × 10⁴ K

A piece of blue glass heated to a high temperature and a piece of red glass at room temperature are taken inside a dimly-lit room. Then,

• The blue piece will look blue and the red piece will look red as usual.

• the red piece will look brighter red and the blue piece will look ordinary blue.

• the blue will look brighter as compared to the red piece.

• Both the pieces will look equal red.

A cup of tea cools from 80°C to 60°C in one minute. The ambient temperature is 30°C. In cooling from 60°C to 50°C. It will take

• 50 sec

• 90 sec

• 60 sec

• 48 sec