Heat Test

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Heat Test - 7

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Question 1
1 / -0

The freezing point of water on a thermometer is 30^o and the boiling point is 150^o. For 40^oC, what will be the reading in the thermometer?

A
68^o

B
78^o

C
88^o

D
74^o

Solution

Let the scale of the thermometer be ⁰X.

Given,

0⁰C = 30⁰X and 100⁰C = 150⁰X

Hence,

So, to convert the ⁰C to ⁰X scale:

Hence, if C = 40⁰C, the reading of the thermometer would be:
Question 2
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A and B are two objects. The temperature of A is greater than that of B. This means that

A
the molecules of A are moving faster on the average than that of B

B
the total energy of A is greater than that of B

C
the average potential energy of A is greater than that of B

D
the heat content of A will always be greater than that of B

Solution

The temperature of an object is a property of the object that determines how hot or cold the body is. It depends on the amount of thermal energy absorbed by the object and also the nature of the object and its mass. Moreover, movement of molecules in an object increases the heat. More the movement, more will be the temperature.
Question 3
1 / -0

The temperature at which Celsius and Fahrenheit scales will show the same reading is

A
0^o

B
– 40^o

C
32^o

D
– 32^o

Solution

The formula for converting between degree Celsius and degree Fahrenheit is:
°C = (°F - 32) x 5/9
To find the temperature when both are equal, we use an old algebra trick and just set ºF = ºC and solve one of the equations.
°C = (°C x 9/5) + 32
°C - (°C x 9/5) = 32
- 4/5 x °C = 32
°C = - 32 x 5/4
°C = - 40
°F = (°F x 9/5) + 32
°F - (°F x 9/5) = 32
- 4/5 x °F = 32
°F = - 32 x 5/4
°F = - 40
So, the temperature when both Celsius and Fahrenheit scales show the same reading is - 40 degrees.
Question 4
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Two spheres of the same size are made of the same metal, but one is hollow and the other is solid. They are heated to the same temperature. What will happen?

A
The hollow sphere will expand more

B
The solid sphere will expand more

C
Both spheres will expand almost equally

D
Neither sphere will expand

Solution

Both the spheres will expand almost equally. This is because both the sphere are of the same material.
Question 5
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Water at 0^oC heats up to 3^oC. Its volume will

A
remain unaltered

B
decrease

C
increase

D
first decrease and then increase

Solution

In general. there is increase in volume of a body when heated and decrease in volume when cooled. But water has a peculiar type of expansion i.e., it contracts from 0°C to 4°C. When water at 0°C is heated, its volume goes on decreasing upto 4°C. At 4°C, it has the least volume and the highest density. On further heating beyond 4°C only the volume of the water increases. Such unusual expansion of water is called anomalous expansion of water.
Question 6
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Which of the following curves best represents the variation of density of water with temperature?

A

B

C

D

Solution

Correct Answer:
Question 7
1 / -0

In a car, radiator and fan are used to cool the engine. The heat transfer modes involved are

A
conduction and convection

B
conduction and radiation

C
radiation and convection

D
conduction, convection and radiation

Solution

Radiation and convection are the processes when the energy is emitted as electromagnetic waves, especially high-energy particles which cause ionization.
Question 8
1 / -0

A person takes hot tea by pouring it into the saucer (plate) when one is in a hurry because he knows that

A
part of heat will be absorbed by the saucer (plate) and the tea will become cold quickly

B
the evaporation increases with the increase in surface area and cooling of tea is faster

C
the latent heat of steam is high and the tea will become cold quickly

D
the high specific heat of water makes the tea cold quickly

Solution

A substance that has a larger surface area will evaporate faster, as there are more surface molecules per unit of volume that are potentially able to escape.
Question 9
1 / -0

The quantity of heat, which crosses unit area of a metal plate during conduction, depends upon

A
density of the metal

B
temperature gradient perpendicular to the area

C
temperature to which the metal is heated

D
area of the metal plate

Solution

The heat transfer through the metal plate per unit time is given by,

Here, is the temperature gradient perpendicular to cross-sectional area.

From above, it is clear that the quantity of heat, which crosses unit area of a metal plate during conduction, depends upon temperature gradient perpendicular to the area.
Question 10
1 / -0

Heat is flowing through two cylindrical rods of the same material. The diameters of the rods are in the ratio 1 : 2, and their lengths are in the ratio 2 : 1. If the temperature difference between their ends is the same, then the ratio of the amounts of heat conducted through them per unit time will be

A
1 : 1

B
2 : 1

C
1 : 4

D
1 : 8

Solution

The thermal resistance of rod, .

Here, l is the length of rod and a is the cross-sectional area of rod.
If d is the diameter of the rod, then a ∝ d².

The heat transfer per unit time is given by,

As it is given that the temperature difference is same for both rods,
Question 11
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Which of the following correctly defines the water equivalent of a body?

A
The mass of alcohol, which will be heated through 1^oC by the amount of heat required to raise the temperature of the body through 1^oC.

B
The mass of water, which will be heated through 1^oC by the amount of heat required to raise the temperature of the body through 1^oC.

C
The mass of water, which will be heated through any range of
temperature.

D
The temperature by which 1 kg of water will be raised by equivalent heat.

Solution

Water equivalent of a substance is defined as the mass of water that will absorb or lose as same quantity of heat as the substance for the same change in temperature.
Question 12
1 / -0

50 g of ice at 0^oC is mixed with 50 g of water at 20^oC. The final temperature of the mixture will be

A
-10^oC

B
-30^oC

C
0^oC

D
10^oC

Solution

Let the temperature of mixture be t⁰C.

While forming the mixture, the heat absorbed by ice will be equal to heat released by water.

Hence,

Here, m₁ is the mass of ice, m₂ is the mass of water, L is the latent heat of freezing of water and s is the specific heat of water.

We know that:

L = 80 cal/g and s = 1 cal/g °C

Hence,

The calculation of temperature gives negative temperature, which is not possible as the ice is already at 0⁰C. Hence, the the minimum possible temperature of the mixture will be 0⁰C.
Question 13
1 / -0

Which of the following has the highest specific heat?

A
Water

B
Mercury

C
Kerosene

D
Copper

Solution

Of the given substances, water has the highest specific heat.
Question 14
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When a body is heated, its temperature will rise if the body

A
does not expand

B
does not change its physical state

C
does not contract

D
changes its physical state

Solution

When a body is heated, its temperature will rise if the body does not change its physical state bacuse energy is lost in changing the state.
Question 15
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Two blocks of ice when pressed together join to form one block of ice because

A
heat is produced during pressing, which melts the ice at the surface of contact of the 2 blocks and fuses them together

B
temperature decreases during pressing, thus lowering the melting point of ice

C
melting point of ice decreases, it melts and solidifies again when pressure is released

D
heat is transferred from the force transfer medium to the contact area, thus melting and fusing the ice

Solution

Two blocks of ice when pressed together join to form one block of ice because heat is produced during pressing which melts the ice at the surface of contact of the 2 blocks, thus fusing them together.
Question 16
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A source of heat supplies heat at a constant rate to a substance. The given figure shows the variation of temperature of the substance with the heat supplied. The slope of segment DE represents

A
latent heat of vaporisation

B
specific heat of vapour

C
thermal capacity of the vapour

D
reciprocal of the thermal capacity of the vapour

Solution

The slope of segment DE represents thermal capacity of the vapour. The rate of temperature increase will be dependent on the heat or thermal capacity of the phase in the system.
Question 17
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A closed vessel is maintained at a constant temperature. It is first evacuated, and then vapour is injected into it continuously. The pressure of the vapours in the vessel

A
increases continuously

B
first increases and then remains constant

C
first increases and then decreases

D
none of the above

Solution

A closed vessel is maintained at a constant temperature. It is first evacuated, and then vapour is injected into it continuously. The pressure of the vapours in the vessel increases continuously.
Question 18
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The door of a running refrigerator inside a closed room was left open. Which of the following observations will be seen?

A
The room will be warmed up gradually.

B
The temperature of the room will remain unaffected.

C
The room will become as cold as the refrigerator.

D
The room will be cooled slightly.

Solution

Refrigerator is a device that transfers heat from inside a box to its surroundings.
If you leave the door open, heat is merely recycled from the room into the refrigerator, then back into the room. A net room temperature increase would result from the heat of the motor that would be constantly running to move energy around in a circle.
Question 19
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The highest temperature reached inside a pressure cooker will depend upon

A
the weight placed upon the vent and the area of the vent

B
the area of the vent and the material being cooked

C
the material being cooked and the weight placed upon the vent

D
the area of the vent only

Solution

Since pressure is directly proportional to surface area. Therefore, the highest temperature reached inside a pressure cooker will depend upon the weight placed upon the vent and the area of the vent.
Question 20
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What happens when vapour condenses into liquid?

A
Its temperature drops.

B
Its temperature rises.

C
It absorbs heat.

D
It evolves heat.

Solution

It evolves heat when vapour condenses into liquid.