Blackbody

Q.

A solid sphere and a hollow sphere of the same material and size are heated to the same temperature and allowed to cool in the same surroundings. If the temperature difference between the surrounding and each sphere is T, then

1. both spheres will cool at the same rate for all values of T

2. both spheres will cool at the same rate only for small values of T.

3. the hollow sphere will cool at a faster rate for all values of T

4. the solid sphere will cool at a faster rate for all values of T

Q. The radiator of a car is painted black. Why?

Q.

The following figure shows two air-filled bulbs connected by a U-tube partly filled with alcohol. What happens to the levels of alcohol in the limbs X and Y when an electric bulb placed midway between the bulbs is lighted

1. The level of alcohol in limb X falls while that in limb Y rises
2. The level of alcohol in limb X rises while that in limb Y falls
3. The level of alcohol falls in both limbs
4. There is no change in the levels of alcohol in the two limbs
   

Q. Two diagonally opposite corners of a square made of a four thin rods of same material, same dimensions are at temperature 40 C and 10 C. If only heat conduction takes place, then the temperature difference between other two corners will be??

Q. Why are radiators in cars painted Black?

Q.

A blackbody of surface area 1 $c{m}^2$ is placed inside an enclosure. The enclosure has a constant temperature 27${}^{\circ }$ C and the blackbody is maintained at 327 ${}^{\circ }$ C by heating it electrically. What electric power is needed to maintain the temperature?$\sigma =6.0\times {10}^{-8}W/m^2-K^4$.

1. 0.56 W

2. 0.37 W

3. 0.73 W

4. 0.65 W

Q. Assertion: We can not receive heat from the Sun through convection.
Reason: Sun is too far away from Earth. The heat from the Sun dissipates mid way.

1. Both assertion and reason are true and the reason is not the correct explanation of the assertion.
2. Both assertion and reason are true and the reason is the correct explanation of the assertion.
3. Assertion is a true statement but the reason is false.
4. Both assertion and reason are false statements.

Q.

Two spherical balls A and B made of the same material, are heated to the same temperature. They are then placed in identical surroundings. If the diameter of A is twice that of B, the ratio of rates of cooling of A and B will be

1. 4:1

2. 1:4

3. 1:1

4. 2:1

Q.

The graph shown in the adjacent diagram, represents the variation of temperature (T) of two bodies, x and y having same surface area, with time (t) due to the emission of radiation. Find the correct relation between the emissivity ($e$) and absorptivity ($a$) power of the two bodies. (IIT JEE 2003)

1. e_y>e_x, a_x> a_y

2. e_x>e_y, a_x> a_y

3. e_x>e_y, a_y> a_x

4. e_y>e_x, a_y> a_x

Q. A black body is heated from ${27}^{\circ }$ C to ${127}^{\circ }$ C. The ratio of their energies of radiations emitted will be

1. 3: 4
2. 9 : 16
3. 27 : 64
4. 81: 256

Q.

The earth receives solar radiation at a rate of 8.2 J/$c{m}^2$ - minute. Assuming that the sun radiates like a blackbody, calculate the surface temperature of the sun. The angle subtended by the sun on the earth is 0.53${}^{\circ }$ and the Stefan constant $\sigma =5.67\times {10}^{-8}W/m^2$ - K4.

1. 6800 K
2. 5800 K
3. 7800 K
4. 7800 K

Q. Do as direct:
The holy man said to the wind : "Is here anyone greater than you?"
The wind said : "Yes, the mountain is greater than me."
(Change into indirect narration)

Q. An ideal black body at room temperature is thrown into a furnace. It is observed that

1. initially it is the darkest body and at later times the brightest
2. it is the darkest body at all times
3. it cannot be distinguished at a times
4. initially it is the darkest body and at later times it cannot be distinguished

Q. A black body of temperature T is inside a chamber of temperature $T_0$. Now the closed chamber is slightly opened to sun such that temperature of black body (T) and chamber $\left(T_0\right)$ remains constant

1. black body will absorb more radiation
2. black body emit more energy
3. black body will absorb less radiation
4. black body emit energy equal to energy absorbed by it

Q. The spectrum from a black body radiation is a

1. Band spectrum
2. Line spectrum
3. Continuous spectrum
4. Line and band spectrum both

Q.

Two spherical balls A and B made of the same material, are heated to the same temperature. They are then placed in identical surroundings. If the diameter of A is twice that of B, the ratio of rates of cooling of A and B will be

1. 1:1

2. 2:1

3. 4:1

4. 1:4

Q. A black body of temperature T is inside a chamber of temperature $T_0$. Now the closed chamber is slightly opened to sun such that temperature of black body (T) and chamber $\left(T_0\right)$ remains constant

1. black body will absorb more radiation
2. black body will absorb less radiation
3. black body emit more energy
4. black body emit energy equal to energy absorbed by it

Q. A copper sphere is suspended in an evacuated chamber maintained at 300 K. The sphere is maintained at a constant temperature of 500 K by heating it electrically. A total of 210 W of electric power is needed to do it. When the surface of the copper sphere is completely blackened, 700 W is needed to maintain the same temperature of the sphere. Calculate the emissivity of copper.

1. 0.5

2. 0.4

3. 0.3

4. 0.2

Q. If the absolute temperature of a black body is doubled, then the percentage increase in the rate of loss of heat by radiation is :

1. 1600%
2. 1500%
3. 16%
4. 15%