Blackbody

Q.

What are good conductors of heat?

Q.

Copper conducts heat better than iron and aluminum.

1. True
2. False

Q.

Why a metal knob appears to be colder than a wooden knob in the same atmosphere.

Q.

Black and dull surfaces absorb less radiation.

1. True
2. False

Q. Which of the following is a real life example of a perfect blackbody?

1. Red hot metal
2. White hot metal
3. Orange hot metal
4. Yellow hot metal

Q.

Why is cathode ray tube evacuated to a low pressure?

Q.

What are good conductors of heat. Give two examples of each.

Q. A polished metal plate with a rough black spot on it is heated to about $1400\text{K}$ and quickly taken to a dark room. The spot will appear

1. darker than the plate surface
2. brighter than the plate surface
3. equally bright as the plate surface
4. equally dark as the plate surface

Q.

What are good conductors of heat? Give two examples.

Q. A polished metallic piece and a black painted wooden piece are kept in open in bright sun for a long time. Then,

1. the wooden piece will absorb less heat than the metallic piece
2. the wooden piece will have a lower temperature than the metallic piece
3. when touched, the metallic piece will be felt hotter than the wooden piece
4. when the two pieces are removed from the open to a cold room, the wooden piece will lose heat at a faster rate than the metallic piece

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. Two bodies $A$ and $B$ are arranged as shown in figure. Which of the following options is correct regarding body $A$?
(Assume that the bodies are placed in an adibatic container)

1. $Q_{emission}<Q_{absorption}$
2. $Q_{emission}=Q_{absorption}$
3. $Q_{emission}>Q_{absorption}$
4. $Q_{emission}=0.5Q_{absorption}$

Q. The radiation from the sun, incident normally at the surface of the earth is $20{\text{kcal/m}}^2\text{min}$. What would have the radiant energy, incident normally on the earth, if the sun had a temperature twice of the present one?

1. $80{\text{kcal/m}}^2\text{min}$
2. $320{\text{kcal/m}}^2\text{min}$
3. $160{\text{kcal/m}}^2\text{min}$
4. $40{\text{kcal/m}}^2\text{min}$

Q. Which of the following is a real life example of a perfect blackbody?

1. Red hot metal
2. White hot metal
3. Orange hot metal
4. Yellow hot metal

Q. The energy radiated by a black body at $2300\text{K}$ is found to have a maximum intensity at a wavelength $1260\text{nm}$, its emissive power being $8000{\text{W/m}}^2$. When the body is cooled to a temperature $T\text{K}$, the emissive power is found to decrease to $500{\text{W/m}}^2$. Find the temperature $T$.

1. $1000\text{K}$
2. $1500\text{K}$
3. $1050\text{K}$
4. $1150\text{K}$

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