Transmission of Heat

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Test1 Max. Marks = 40

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1.The thickness of a metallic plate is 0.4 cm. The temperature between its two surfaces is 20 ⁰C. The quantity of heat flowing per second is 50 calories from 5 cm² area. In CGS system, the coefficient of thermal conductivity will be

4 points

(a) 0.4

(b) 0.6

(d) 0.5

Clear selection

2. A slab consists of two parallel layers of copper and brass of the same thickness and having thermal conductivities in the ratio 1 : 4. If the free face of brass is at 100 ⁰C and that of copper at 0 ⁰C, the temperature of interface is

4 points

(a) 80°C

(b) 20°C

(d) 40°C

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3. Two spheres of different materials one with double the radius and one-fourth wall thickness of the other, are filled with ice. If the time taken for complete melting ice in the large radius one is 25 minutes and that for smaller one is 16 minutes, the ratio of thermal conductivities of the materials of larger sphere to the smaller sphere is

4 points

(a) 4 : 5

(b) 5 : 4

(d) 1 : 25

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4.The ratio of the coefficient of thermal conductivity of two different materials is 5 : 3. If the thermal resistance of the rod of same thickness resistance of the rods of same thickness of these materials is same, then the ratio of the length of these rods will be

4 points

(a) 3 : 5

(b) 5 : 3

(d) 3 : 2

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5.Relation between emissivity e and absorptive power a is (for black body)

4 points

(a) e = a

(b) e = 1/a

(d) a = e²

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6. There is a rough black spot on a polished metallic plate. It is heated upto 1400 K approximately and then at once taken in a dark room. Which of the following statements is true

4 points

(a) In comparison with the plate, the spot will shine more

(b) In camparison with the plate, the spot will appear more black

(d) The plate and the black spot can not be seen in the dark room

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7.The wavelength of maximum emitted energy of a body at 700 K is 4.08 μm. If the temperature of the body is raised to 1400 K, the wavelength of maximum emitted energy will be

4 points

(a) 1.02 μm

(b) 16.32 μm

(d) 2.04 μm

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8. Two spheres P and Q, of same colour having radii 8 cm and 2 cm are maintained at temperatures 127 °C and 527 °C respectively. The ratio of energy radiated by P and Q is

4 points

(a) 0.054

(b) 0.0034

(d) 2

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9.A body radiates energy 5W at a temperature of 127 °C. If the temperature is increased to 927 °C, then it radiates energy at the rate of

4 points

(a) 410W

(b) 81W

(d) 200W

Clear selection

10. The energy spectrum of a black body exhibits a maximum around a wavelength λ₀. The temperature of the black body is now changed such that the energy is maximum around a wavelength 3λ₀/4.The power radiated by the black body will now increase by a factor of

4 points

(a) 256/81

(b) 64/27

(d) 4/3

Clear selection

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