# Class 11th Physics – 11 Thermal properties of matter MCQs

#### A disc is rotating about an axis which passes through its centre and perpendicular to its plane. When the temperature of the disc is slowly increased, its angular velocity of rotation ___.

A disc is rotating about an axis which passes through its centre and perpendicular to its plane. When the temperature of the disc is slowly increased, its angular velocity of rotation decreases. As the temperature of the disc increases, it expands and hence its moment of inertia increases. According to law of conservation of angular momentum, when the moment of inertia increases, the angular velocity decreases, since the angular momentum remains constant in the absence of any external torque.

#### A graph is plotted with (PV) on y-axis and V on x-axis where P and V denote the pressure and volume of a fixed mass of gas respectively. At constant temperature, the graph is a ____.

At constant temperature, we know that PV = k where k is a constant for a fixed mass of a gas. Since (PV) = k, this implies that the graph represents a straight line, y = k, which is a straight line parallel to the x-axis. Hence option B is correct

#### Statement A: In winter, a steel chair appears colder than a wooden chair. Statement B: Steel is a better conductor than wood. So, heat flowing into steel from us is conducted away quickly and hence more heat flows into it and it appears colder.

Statement A: In winter a steel chair appears colder than a wooden chair. Statement B: Steel is a better conductor than wood. So, heat flowing into steel from us is conducted away quickly and hence more heat flows into it and it appears colder. Both A and B are true statements.

#### When water of mass 'm' at 80°C is added to 2 kg of ice at 0 °C in a calorimeter, all the ice just melts to form water at 0 °C. Then, m is ____ kg. Take specific heat capacity of water as 1 cal g-^{1}°C^{-1}, latent heat of fusion of ice as 80 cal g^{-1} and the thermal capacity of the calorimeter to be negligible.

The mass of water m is 2kg.

Given, mass of ice, m_{i} = 2 kg = 2000g

Mass of water added to ice in the calorimeter, m_{w} = m

Specific heat capacity of water, s_{w} = 1 cal g^{-1} °C^{-1}

Initial temperature of the water = 80 °C

Final temperature of the mixture = 0°C

Since the calorimeter is of negligible heat capacity, it does not gain any heat from the steam.

Here, ice gains heat from water to convert from ice at 0 °C to water at 0 °C.

According to the principle of mixtures,

Heat lost by the water = Heat gained by the ice

m_{w}s_{w} (80 - 0) = m_{i}L_{f}

m × 1 × 80 = 2000 × 80

m = 2000g = 2 kg

#### Pick the wrong statement/statement(s) in the following options____.

"The thermal conductivity of a material depends on its area of cross section.” This is the wrong statement, The thermal conductivity of a material depends only on the nature of material. Materials with large thermal conductivities are better conductors than those with smaller values of K.

#### A bucket contains 500 g of water at 25 °C. 1500 g of hot water at 100 °C is now added to the water in the bucket. Assuming the heat gained by the bucket is negligible, the amount of heat gained by the water in the bucket is ____cal.

The amount of heat gained by the water in the bucket is 28125 cal.

Given mass of water in the bucket, m_{1} = 500 g

Mass of hot water added, m_{2} = 1500 g

Specific heat of the water, s_{w} = 1 cal g-^{1}°C^{-1}

Initial temperature of the water in the bucket = 25 °C

Initial temperature of the hot water = 100 °C

Let the resultant temperature of the mixture be t. The bucket gains negligible amount of heat.

Hence, according to the principle of mixtures,

Heat lost by the hot water = Heat gained by the cold water

m_{2}s_{w} (100 - t) = m_{1}s_{w} (t -25)
1500 × 1 × (100 - t) - 500 × 1 × (t - 25)
Solving for t, we get t = 81.25°C

Hence, heat gained by the cold water = m_{1}s_{w }(t - 25)
= 500 × 1 × (81.25 - 25) = 28125 cal.

#### Statement A: During winter, a farmer waters his crops during the evening, to prevent damage to the crop from frost. Statement B: Water has high specific heat capacity. State which statement/s is true?

Statement A: During winter, a farmer waters his crops during the evening, to prevent damage of the crop from frost. Statement B: Water has high specific heat capacity. Water has very high specific heat capacity. In winter season, it is advisable to water the crops in the evening time. The water given to the crops liberates enough heat during the night in the process of cooling down, because of its very high specific heat capacity. This prevents damage to the crop from frost. Hence, both A and B are true.

#### The specific heat capacity of a system in a process where it neither gains nor loses heat but suffers a change in its temperature is ____.

The specific heat capacity of a system in a process where it neither gains nor loses heat but suffers a change in its temperature is zero.
Specific heat capacity s=(1/m)(dQ/dt)

Here dQ = 0, but dt is finite.

Specific heat capacity s=(1/m)(dQ/d)t=0

#### Pick the wrong statement/statement(s) in the following options.

The statement B is wrong since, the size of the degree on Centigrade scale of temperature is equal to the size of the degree on the absolute scale of temperature, since the change in temperature recorded on the Centigrade scale is the same as that recorded on the absolute scale of temperature.

#### The specific heat capacity of a substance depends on ____.

The specific heat capacity of a substance depends on its nature and temperature. The specific heat capacity of a substance depends on the nature of material and its temperature.

#### The Fahrenheit scale of temperature is considered to be more accurate than the Centigrade scale of temperature since ____.

the Fahrenheit scale of temperature is considered to be more accurate than the Centigrade scale of temperature since it has more equal intervals between the ice point and the steam point of water when compared to the Centigrade scale of temperature. Between the ice point and the steam point, there are 180 equal intervals on a Fahrenheit scale of temperature, whereas there are only 100 equal intervals on a Centigrade scale of temperature. Hence, Fahrenheit scale of temperature is considered to be more accurate than Centigrade scale of temperature.

#### The temperature at which the Fahrenheit and Centigrade scales of temperature record the same reading is ____.

The temperature at which the Fahrenheit and Centigrade scales of temperature record the same reading is -40°C.

Let the reading on the Centigrade scale of temperature be C = x

Then the reading on the Fahrenheit scale of temperature will be F = x

We know that,

C/100=F-32/180

C/5=F-32/9

x/5 = x-32/9

Solving, we get x = -40°C.

#### Statement A: Volume of a liquid varies due to variations in temperature. Statement B: Liquid in glass type thermometers uses the property of variation in volume of a liquid with temperature.

Statement A: Volume of a liquid varies due to variations in temperature. Statement B: Liquid in glass type thermometers uses the property of variation in volume of a liquid with temperature. Liquids expand or contract due to variations in temperature. Hence, statement A is true. We come across clinical thermometers or lab thermometers, which are liquid- in- glass type thermometers. When the bulb of the thermometer is in contact with a substance, the mercury in the bulb expands or contracts to read the temperature of the substance. Here the property of variation in volume of a liquid with temperature is used. Hence, the statement B is true.

#### A body of mass 2 kg requires 9800 J of heat to raise its temperature from 10° C to 20° C without change in its state. The specific heat capacity of the material of the body is ____ Jkg^{-1}K^{-1}.

The specific heat capacity of the material of the body is 490 Jkg^{-1}K^{-1 }
.Given, heat supplied dQ = 9800 J
Mass of the body, m = 2 kg
Rise in its temperature dt = (t_{2} - t_{1}) = 20 - 10 = 10 K
(Change in Celsius is equal to the change in absolute scale of temperature)
Specific heat capacity s=(1/m)(dQ/dt)=1/2(9800/10)=490 jkg^{−1}K^{−1}

#### Natural convection cannot occur ____.

Natural convection cannot occur in an artificial satellite in space. This is because of the fact that natural convection cannot occur in gravity free space. In the options A, B and D, there is gravity and hence there is a possibility of natural convection.

#### The principle of mixtures is a direct consequence of the law of conservation of ____.

The principle of mixtures is a direct consequence of the law of conservation of energy. Law of conservation of energy is the basis for the principle of mixtures, since heat is only exchanged between the contents of the mixture.

#### Among the given options, the process of convection does not form the basis for ____.

Among the given options, the process of convection does not form the basis for transfer of heat through vacuum. This is because of the fact that convection does not occur in vacuum.

#### Four rods of equal area of cross-section and length have the same temperature difference across them, but are made of copper, silver, aluminium and lead respectively.

The rate of conduction is maximum through the rod made of silver.
Rate of conduction, Q/t = KA (T_{1}-T_{2})/ l
Since all the rods are of same length, area of cross-section and have same temperature difference across them, the rod with maximum thermal conductivity has the maximum rate of conduction through it.
Here, silver has maximum thermal conductivity and hence has the highest rate of conduction through it.

#### A change in temperature of 20°C corresponds to a change in temperature of ____°F.

A change in temperature of 20°C corresponds to a change in temperature of 36°F.

Given, change in temperature recorded on Centigrade scale, ΔC = 20°C

Corresponding change in temperature recorded on Fahrenheit scale,
ΔF =?

We know that,

C/100=F-32/180

⇒ΔC/5=ΔF/9

20/5=ΔF/9

ΔF = 36°F

#### A and B, have masses 2 kg and 5 kg respectively. The same amount of heat is required to raise the temperatures of A and B through 20 K and 60 K respectively.

The ratio of the specific heat capacity of A to that of B is 15:2.
Given mass of A, m_{1} = 2 kg

Mass of B, m_{2 }= 5 kg

Rise in temperature of A, (dt)_{1} = 20 K

Rise in temperature of B, (dt)_{2} = 60 K

Ratio of specific heat capacities, s_{1}/s_{2}=?

We know dQ = ms (dt)

#### In the given options, during change of state of a substance, the physical quantities associated with the substances that are not constant are____.

During change of state of a substance, the physical quantities associated with the substance that are not constant is both volume and density. Theses change with change in state.

#### The predominant mechanism for heat transfer inside a human body is ____.

The predominant mechanism for heat transfer inside a human body is forced convection. In a human body, the heart serves as the pump and the blood as the circulating fluid, giving rise to forced convection.

#### Heat is a form of energy which is transferred between a system and its surroundings due to ____.

Heat is a form of energy which is transferred between a system and its surroundings due to difference in their temperatures. Heat is a form of energy that is transferred between two systems or a system and its surrounding, when there exists a difference in temperature between them.

#### When thermal radiation is incident on a material, ____.

When thermal radiation is incident on a material, part of it is absorbed and part of it is reflected, depending on its colour. This is because of the fact that, the amount of radiation absorbed by it varies with the colour of the body. For example, we know that black clothes are better absorbers, than clothes of other colours.

#### One litre of oxygen, hydrogen, nitrogen and carbon-dioxide are considered at S.T.P. The gas which has greatest mass is ____.

One litre of oxygen, hydrogen, nitrogen and carbon-dioxide are considered at S.T.P. The gas which has greatest mass is carbon-dioxide. Given, that all the gases occupy equal volume V, at S.T.P. Hence they are at same absolute temperature T and pressure P. According to ideal gas equation, PV = µRT (R is universal gas constant, µ is the number of moles of the gas) Here μ=m/M Where m and M are the mass and molecular weight of the gas respectively. PV= (m/M) RT PVM = mRT Here, P, V, R and T are constants. m∝M Hence, the gas which has the largest molecular weight M has the largest mass ‘m’. Among oxygen, hydrogen, nitrogen and carbon-dioxide, the gas having greatest molecular weight is carbon-dioxide. Hence carbon-dioxide has the largest mass among the given options.

#### A uniform 'AB' metal rod of length 2 m has its end A maintained at 100° C and end B maintained at 0° C. In steady state, the temperature at a distance of 0.5 m from the end A in the rods is ____°C.

In steady state, the temperature at a distance of 0.5 m from the end A in the rods is 75° C.

Given the temperature difference across AB is (T_{A} - T_{B}) = 100°C

In steady state, the rate of conduction is constant throughout the rod.

Hence Q/t = KA (T_{1}-T_{2})/ l = constant.

Therefore for any part of the rod T_{1}-T_{2}/l = constant.

Let the point C be at distance 0.5 m from A

Now, we have T_{A}-T_{B}/l_{AB} = T_{A}-T_{C }/l_{AC}

100-0/2 = 100-T_{C }/0.5

100/2 = 100-T_{C}/0.5

Solving, we get T_{C} = 75° C

#### The specific heat capacity of a system in a process, in which it gains heat without any change in its temperature is ____.

The specific heat capacity of a system in a process, in which it gains heat without any change in its temperature, is infinity. Specific heat capacity s=(1/m)(dQ/dt) Here dQ = +ve but dt = 0 Specific heat capacity s=(1/m)(dQ/dt)=∞

#### Statement A: Gases deviate from their ideal behaviour at low temperatures. Statement B: At low temperatures, the molecular attractions become significant, leading to a deviation from the ideal behaviour for a gas.

At high temperatures, the molecular motion readily overcomes the molecular attractions and the molecules move about as though there were no molecular attraction. But at low temperatures the molecular attractions become significant and this leads to a deviation from the ideal behaviour for a gas. Hence A and B are true.

#### In the process of natural convection, ____.

In the process of natural convection, the movement of fluid occurs due to differences in density. When a liquid is heated, the hotter layers move up since they are of lesser density than the colder layers on top of it. Thus, the hotter layer is replaced by the colder layer, due to difference in densities.

#### When glaciers melt, they start melting from the bottom. This is due to the fact that,____.

When glaciers melt, they start melting from the bottom. This is due to the fact that, the melting point of ice is lowered with increase in pressure.

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