Two conductors of the same material have their diameters in the ratio 1 : 2 and their lengths in the ratio 2 : 1. If the temperature difference between their ends is the same, then the ratio of amounts of heat conducted per second through them will be

• 4 : 1

• 1 : 4

• 8 : 1

• 1 : 8

52.

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 red will look as usual

• red looks bnghter red and blue looks ordinary blue

• blue shines like brighter red compared to the red piece

• both the pieces will look equally red

The wavelength of the radiation emitted by a body depends upon

• the nature of the surface

• the area of the surface

• the temperature of the surface

• all of the above factors

Infrared radiation was discovered in 1800 by

• William Wollaston

• William Herschel

• Wilhelm Roentgen

• Thomas Young

The freezer in a refrigerator is located at the top section so that

• the entire chamber of the refrigerator is cooled quickly due to convection

• the motor is not heated

• the heat gained from the environment is high

• the heat gained from the environment is low

The sprinkling of water reduces slightly the temperature of a closed room because

• temperature ofwater is less than that of the room

• specific heat of water is high

• water has large latent heat of vaporisation

• water is a bad conductor of heat

Two identical rods AC and CB made of two different metals having thermal conductivities in the ratio 2 : 3 are kept in contact with each other at the end C as shown in the figure. A is at 100°C and B is at 25°C. Then the junction C is at

• 55°C

• 60°C

• 75°C

• 50°C

The surface temperature of the sun which has maximum energy emission at 500 nm is 6000 K. The temperature of a star which has maximum energy emission at 400 nm will be

• 8500 K

• 4500 K

• 7500 K

• 6500 K

The coefficient of thermal conductivity of copper is 9 times that of steel. In the composite cylindrical bar shown in the figure, what will be the temperature at the junction of copper and steel ?

• 75°C

• 67°C

• 25°C

• 33°C

If a black body emits 0.5 J of energy per second when it is at 27°C, then the amount of energy emitted by it when it is at 627°C will be

• 40.5 J

• 162 J

• 13.5 J

• 135 J