Question: Absorptivity of a body will be equal to its emissivity___________________?

• 1. at all temperatures
• 2. at one particular temperature
• 3. when system is under thermal equi-librium
• 4. at critical temperature

Question: The amount of radiation mainly depends on___________________?

• 1. nature of body
• 2. temperature of body
• 3. type of surface of body
• 4. all of the above

Question: The ratio of the energy absorbed by the body to total energy falling on it is called_________________?

• 1. absorptive power
• 2. emissive power
• 3. absorptivity
• 4. emissivity

Question: The emissive power of a body depends upon its___________________?

• 1. temperature
• 2. wave length
• 3. physical nature
• 4. all of the above

Question: 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is____________________?

• 1. 0.45
• 2. 0.55
• 3. 0.40
• 4. 0.75

Question: The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit_______________?

• 1. temperature
• 2. thickness
• 3. area
• 4. time

Question: According to Stefan’s law, the total radiation from a black body per second per unit area is proportional to____________________?

• 1. absolute temperature
• 2. T2
• 3. T5
• 4. t

Question: The thermal diffusivities for solids are generally__________________?

• 1. less than those for gases
• 2. jess than those for liquids
• 3. more than those for liquids and gases
• 4. more or less same as for liquids and gases

Question: The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as_________________?

• 1. Krichoff’s law
• 2. Stefan’s law
• 3. Wien’ law
• 4. Planck’s law

Question: Depending on the radiating properties, a body will be white when_________________?

• 1. p = 0, x = 0 and a = 1
• 2. p=l,T = 0anda = 0
• 3. p = 0, x = 1 and a = 0
• 4. x = 0, a + p = 1