JEE 2020 Revision :Transfer of Heat

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Question 1

2 kg of ice at –20 °C is mixed with 5 kg of water at 20 °C in an insulating vessel having a negligible heat capacity. Calculate the final mass of water remaining in the container.
It is given that the specific heats of water and ice are 1 kcal/kg/ °C and 0.5 kcal/kg/ °C while the latent heat of fusion of ice is 80 kcal/kg.

• A7 kg
• B6 kg
• C4 kg
• D2 kg

Question 2

Two spheres of different materials one with double the radius and one-fourth wall thickness of the other, are filled with same amount of 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 –

• A4 : 5
• B5 : 4
• C25 : 1
• D1 : 25

Question 3

Three rods made of same material and having the same cross-section have been joined as shown in figure. Each rod is of the same length. The left and right ends are kept at 0 °C, 90 °C & 60 °C. The temperature of the junction of the rods will be

• A45 °C
• B50 °C
• C55 °C
• D60 °

Question 4

Three friends Richard, Newton, and Jim choose a sphere, cube, and a thin circular plate respectively. All have the same material and same mass are initially heated to same high temperature. Then

• APlate will cool fastest and cube the slowest
• BSphere will cool fastest and cube the slowest
• CPlate will cool fastest and sphere the slowest
• DCube will cool fastest and plate the slowest.

Question 5

Which of the following is more close to a black body?

• ABlack board paint
• BGreen leaves
• CRed roses
• DNone of these

Question 6

A, B and C are the three identical conductors but made from different materials. They are kept in contact as shown.

Their thermal conductivities are K, 2K and . The free end of A is at 100 ºC and the free end of C is at 0 ºC. During steady state, the temperature of the junction of A and B is nearly..... ºC.

• A71
• B29
• C63
• D37

Question 7

Three rods of the same dimensions have thermal conductivities 3k, 2k and k. They are arranged as shown, with their ends at 100 °C, 50 °C and 0 °C. The temperature of their junction is –

• A75 °C
• B
• C40 °C
• D

Question 8

Radius of a conductor increases uniformly from left end to right end as shown if figure. Material of the conductor is isotropic and its curved surface is thermally isolated from surrounding. Its ends are maintained at temperatures T₁ and T₂ (T₁>T₂).

If, in steady state, heat flow rate is equal to H, then which of the following graphs is correct–

• A
• B
• C
• D

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