Thermal Properties of Matter

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

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

A steel scale measures the length of a copper wire as 80.0 cm, when both are at 20C, the calibration temperature for the scale. What would the scale read for the length of the rod when both are at 40°C?

Given α for steel = 11 × 10^-6 per ^oC and 

α for Cu = 11×10^-6 per ^oC

• 80.0096 cm

• 80.0272 cm

• 1 cm

• 25.2 cm