Convection

Q.

The process by which heat flows from the region of higher temperature to the region of lower temperature by actual movement of material particles is called

1. Sublimation

2. Radiation

3. Convection

4. Conduction

Q.

The velocity of heat radiation in vacuum is

1. Equal to that of light

2. Less than that of light

3. Equal to that of sound

4. Greater than that of light

Q. 12.What is the expression for rate of fall in temperature for small temperature difference with surrounding

Q. 37, If a metallic sphere gets cooled from 62 C to 50C in 10 minutes and in the next 10 minutes gets cooled to42 C, then the temperature of the surroundings is(1) 30^° C(3) 26^° 0C(2) 36^° C(4) 20^° C

Q. A spherical body having radius $0.5\text{m}$ is transfering heat to its surrounding through convection. Find the temperature difference between surrounding and the body surface, if the rate of heat transfer is $1.57\times {10}^5\text{W}$.
(Convection coefficient, $h_c=1570{\text{W/m}}^2\text{-K}$)

1. $35.8\text{K}$
2. $31.8\text{K}$
3. $38.8\text{K}$
4. $40.8\text{K}$

Q. What is the role of gravitational force in convection?

Q. Question) An ideal heat engine working between T₁ and T₂ has efficiency $\eta$. When T₁ is doubled and T₂ is halved, efficiency becomes / remains $(T_1>T_2)$.
$\left(3\right)\frac{\eta +3}{4}$

Q. A body cools from ${60}^{\circ }\text{C}$ to ${50}^{\circ }\text{C}$ in $10$ minutes. If the room temperature is ${25}^{\circ }\text{C}$ then the temperature of the body at the end of the next $10$ minutes will be

1. ${38.50}^{\circ }\text{C}$
2. ${40.25}^{\circ }\text{C}$
3. ${42.86}^{\circ }\text{C}$
4. ${45.75}^{\circ }\text{C}$

Q. A body initially at ${80}^{\circ }\text{C}$ cools to ${64}^{\circ }\text{C}$ in $5$ minutes and to ${52}^{\circ }\text{C}$ after another $5$ minutes. The temperature of the surroundings is

1. ${15}^{\circ }\text{C}$
2. ${16}^{\circ }\text{C}$
3. ${20}^{\circ }\text{C}$
4. ${25}^{\circ }\text{C}$

Q.

Refrigerators X and Y are removing 1000 J of heat from the freezer. Refrigerator X is working between -5^o C and 25^o C and refrigerator Y is working between -20^o C and 20^oC. Find efficiency of refrigerator X and Y?

1. 8.9, 7.3

2. 9.8, 7.3

3. 7.9, 6.5

4. 20, 2

Q. Adhesion enables us to write on blackboard with chalk.

1. False
2. True

Q.

A sphere, a cube and a thin circular plate have the same mass and are made of the same material. All of them are heated to the same temperature. The rate of cooling is

1. the maximum for the sphere and minimum for the plate

2. the maximum for the sphere and minimum for the cube

3. the maximum for the plate and minimum for the sphere

4. the same for all the three.

Q. 60. A solid cube and a solid sphere of the same material have equal surface area. both of temperature 120? then which will cool faster and which will cool slower

Q. 16.A sphere of radius r specific heat s is rotated about an axis passing through its centre at a speed of n rotations per second. It is suddenly stopped and 50% of its energy is used in increasing its temperature. Then the rise in temperature of the sphere is A. (2/5)π²n²r²/s B. (1/10)π²n²/r²s C. (7/8)πr²n²s D. 5[πrn/145]²

Q. A body cools down from ${40}^{\circ }\text{C}$ to ${35}^{\circ }\text{C}$ in $10$ minutes and to ${30}^{\circ }\text{C}$ in another $15$ minutes. Find the temperature of the surroundings.

1. ${20}^{\circ }\text{C}$
2. ${22.5}^{\circ }\text{C}$
3. ${25}^{\circ }\text{C}$
4. ${27}^{\circ }\text{C}$

Q. In which method of heat transfer, gravity does not play a part?

Q. Which of the following curves shows correct relation between convective resistance $\left(R\right)$ and radius of hot sphere $\left(r\right)$ being placed in a stream of cold air ?

1. 
2. 
3. 
4. 

Q. A body cools from 80 °C to 50 °C in 5 minutes. Calculate the time it takes to cool from 60 °C to 30 °C. The temperature of the surroundings is 20 °C.

Q. Heat current depends on thermal conductivity, area, temperature difference and dimension of object

1. False
2. True

Q. A spherical body having radius $0.5\text{m}$ is transfering heat to its surrounding through convection. Find the temperature difference between surrounding and the body surface, if the rate of heat transfer is $1.57\times {10}^5\text{W}$.
(Convection coefficient, $h_c=1570{\text{W/m}}^2\text{-K}$)

1. $35.8\text{K}$
2. $31.8\text{K}$
3. $38.8\text{K}$
4. $40.8\text{K}$