Which of the following is more close to a black body?
  • Green leaves
  • Black holes
  • Blackboard paint
  • red roses
Consider two rods of same length and different specific heats $(S_1 , S_2 )$, conductivities $(K_1 , K_2 )$ and area of cross-sections $(A_1 , A_2 )$ and both having temperature $T_1$ and $T_2$ at their ends. If the rate of loss of heat due to conduction is equal, then
  • $K_1 A_1 = K_2 A_2$
  • $K_1 \frac{A_1}{S_1} = K_2 \frac{A_2}{S_2}$
  • $K_2 A_1 = K_1 A_2$
  • $K_2 \frac{A_1}{S_2} = K_1 \frac{A_2}{S_2}$
Unit of Stefan’s constant is
  • $Watt\, m^2 K^4$
  • $Watt\, m^2/K^4$
  • $Watt/m^2\, K $
  • $Watt/m^2\, K^4$
On a cold morning, a metal surface will feel colder to touch than a wooden surface, because
  • Metal has a high specific heat
  • Metal has a high thermal conductivity
  • Metal has a high specific heat
  • Metal has a low thermal conductivity
The sprinkling of water reduces slightly the temperature of a closed room, because
  • the temperature of the water is less than that of the room.
  • specific heat of water is high
  • water has a large latent heat of vaporization.
  • water is bad conductor of heat
If the temperature of the sun is doubled, the rate of energy received on earth will be increased by a factor
  • 16
  • 8
  • 4
  • 2
The ratio of the thermal conductivity of two rods of different material is 5 :The two rods of same area of cross-section and same thermal resistance will have the length in the ratio
  • 4 : 5
  • 1 : 9
  • 5 : 4
  • 9 : 1
Three rods of equal length of thermal conductivities k, 2k and 3k are symmetrically joined to a point. If temperature of ends are 0° C, 50 ° C and 100 ° C respectively. What is the temperature of the junction?
  • 24 ° C
  • 28 ° C
  • 66.66 ° C
  • 33.33 ° C
Three discs, A, B and C having radii 2m, 4m and6m respectively are coated with carbon black on their outer surfaces. The wavelengths corresponding to maximum intensity are 300nm, 400nm and 500 nm, respectively. The power radiated by them are $Q_A$, $Q_B$ and $Q_C$ respectively
  • $Q_A$ is maximum
  • $Q_B$ is maximum
  • $Q_C$ is maximum
  • $Q_A = Q_B = Q_C$
In the following question, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given responses. Assertion: Water kept in an open vessel will quickly evaporate on the surface of the moon. Reason: The temperature at the surface of the moon is much higher than the boiling point of water.
  • If both assertion and reason are true and the reason is the correct explanation of the assertion.
  • If both assertion and reason are true but the reason is not the correct explanation of the assertion.
  • If the assertion is true, but the reason is false
  • If both assertion and reason are false
  • If the reason is true but the assertion is false
In the following question, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given responses. Assertion: A hollow metallic closed container maintained at a uniform temperature can act as a source of black body radiation. Reason: All metals act as a black body.
  • If both assertion and reason are true and the reason is the correct explanation of the assertion.
  • If both assertion and reason are true but the reason is not the correct explanation of the assertion.
  • If the assertion is true, but the reason is false
  • If both assertion and reason are false
  • If the reason is true but the assertion is false
In the following question, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given responses. Assertion: Blue star is at high temperature than red star. Reason: Wein’s displacement law states that $T \alpha (1/ \lambda_m).
  • If both assertion and reason are true and the reason is the correct explanation of the assertion.
  • If both assertion and reason are true but the reason is not the correct explanation of the assertion.
  • If the assertion is true, but the reason is false
  • If both assertion and reason are false
  • If the reason is true but the assertion is false
In the following question, a statement of assertion is followed by a statement of reason. You are required to choose the correct one out of the given responses. Assertion: A brass tumbler feels much colder than a wooden tray on a chilly day. Reason: The thermal conductivity of brass is less than that of wood.
  • If both assertion and reason are true and the reason is the correct explanation of the assertion.
  • If both assertion and reason are true but the reason is not the correct explanation of the assertion.
  • If the assertion is true, but the reason is false
  • If both assertion and reason are false
  • If the reason is true but the assertion is false
An electric heater is used in a room with a total wall area of $137m^2$ to maintain a temperature of +20 C inside it when the outside temperature is −10C. The walls have three different layers of materials. The innermost layer is of wood thickness 2.5cm, the middle layer is of cement of thickness 1.0cm and the outermost layer is of brick of thickness 25.0cm. Assume that there is no heat loss through the floor and the ceiling. The internal conductivities of wood, cement and brick are 0.125,1,5 and 1.0 watt/m/ ° C respectively. What is the equivalent thermal conductivity of the wall?
  • .512 watt/m/ ° C
  • .624 watt/m/ ° C
  • .134 watt/m/ ° C
  • .986 watt/m/ ° C
Find the power of the electric heater
  • 1000 W
  • 8000 W
  • 9000 W
  • 11000 W
The temperature of the sun is measured with
  • pyrometer
  • gas thermometer
  • Platinum resistance thermometer
  • vapor pressure thermometer
The coefficient of linear expansion of brass and steel are $\alpha _1$ and $\alpha _2$. If we take a brass rod of length $l_1$ and steel rod of length $l_2$ at 0 ° C and their difference in length ($l_2 −l_1$) will remain the same at all temperatures if
  • $\alpha _1 l_1=\alpha _2 l_2$
  • $\alpha _1 l_2=\alpha _2 l_1$
  • $\alpha _1^2 l_1=\alpha _2^2 l_2$
  • $\alpha _1 l_2^2=\alpha _2 l_1^2$
Woolen clothes keep the body warm because wool
  • decreases the temperature
  • increases the temperature of the body
  • is a bad conductor
  • all of these
Emissive and absorptive power of material at 2000K is 8 and 10 respectively, calculate the emissivity of IBB (ideal black body
  • 0.2
  • 0.4
  • 0.6
  • 0.8
0 h : 0 m : 1 s

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