# NIOS Class 10 Science and Technology Chapter 14 Thermal Energy

NIOS Class 10 Science and Technology Chapter 14 Thermal Energy Solutions to each chapter is provided in the list so that you can easily browse through different chapters NIOS Class 10 Science and Technology Chapter 14 Thermal Energy and select need one. NIOS Class 10 Science and Technology Chapter 14 Thermal Energy Question Answers Download PDF. NIOS Study Material of Class 10 Science and Technology Notes Paper 212.

## NIOS Class 10 Science and Technology Chapter 14 Thermal Energy

Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 10 Science and Technology Chapter 14 Thermal Energy, NIOS Secondary Course Science and Technology Solutions for All Chapters, You can practice these here.

### Thermal Energy

Chapter: 14

INTEXT QUESTIONS 14.1

1. State whether the following statements are true or false:

(i) Heat can be measured in kelvin.

Ans: False.

(ii) –30° F is a lower temperature than –30° C.

Ans: False.

(iii) The numerical value of temperature of any hot body measured on kelvin’s scale is always higher than the value on Fahrenheit scale.

Ans: True.

(iv) Thermal energy can be measured either in calories or in joules.

Ans: True.

(v) Pure alcohol can also be used as a thermometric liquid.

Ans: True.

(vi) A body is felt cold when heat flows from our body to that body.

Ans: True.

INTEXT QUESTIONS 14.2

Fill in the blanks with the correct choice.

1. A bimetallic strip is used as a thermostat in the electrical device named …………….. (electric bulb, T.V., refrigerator).

Ans: Refrigerator.

2. Melting point of 1 kg wax will be …………….. the melting point of 2 kg wax (double, half, same as).

Ans: Same as.

3. Latent heat of evaporation is measured in …………….. (J, J/K, J/kg).

Ans: J/kg.

4. 1 kg steam at 100 °C has 2260 J …………….. heat than water at 100 °C (more, less).

Ans: More.

5. The cubical expansivity of a substance is …………….. its linear expansivity (equal to, two times, three times).

Ans: Three times.

6. The expansivity of …………….. is maximum. (solids, liquids, gases).

Ans: Gases.

INTEXT QUESTIONS 14.3

Choose the correct alternative

1. Two iron balls of radii r and 2r are heated to the same temperature. They are dropped in two different ice boxes A and B respectively. The mass of ice melted.

(a) Will be same in the two boxes.

(b) In A will be twice than in B.

(c) In B will be twice than that in A.

(d) In B will be four times than that in A.

Ans: (c) In B will be twice than that in A.

2. An iron ball A of mass 2 kg at temperatures  20°C is kept in contact with another iron ball.

B of mass 1.0 kg at 20°C. The heat energy will flow.

(a) From A to B only.

(b) From B to A only.

(c) In neither direction.

(d) Initially from A to B and then from B to A.

Ans: (d) Initially from A to B and then from B to A.

3. When solid ice at 0°C is heated, its temperature.

(a) Rises.

(b) Falls.

(c) Does not change until whole of it melts.

(d) First rises then falls back to 0°C.

Ans: (c) does not change until the whole of it melts.

4. When steam at 100°C is heated its temperature

(a) Does not change.

(b) Increases.

(c) Decreases.

(d) None of these.

Ans: (b) Increases.

5. Specific heat of aluminium is almost two times the specific heat of copper. Equal amount of heat is given to two pieces of equal masses of copper and iron respectively. Rise in temperature of:

(a) Copper will be equal to that of aluminium.

(b) Copper will be twice the rise in temperature of aluminium.

(c) Copper will be half the rise in temperature of aluminium.

(d) Copper will be four times the rise in temperature of aluminium.

Ans: (b) Copper will be twice the rise in temperature of aluminium.

6. Equal heat is given to three pieces of copper A, B, and C having masses in the ratio 1:2:3. The rise in temperature will be in the order.

(a) A > B > C.

(b) B > C > A.

(c) C > B > A .

(d) A > C > B.

Ans: (a) A > B > C.

1. Distinguish clearly between heat and temperature.

Ans: Heat refers to the amount of energy in an object, measuring the total kinetic and potential energy contained by the molecules in that object. Temperature refers to the intensity of heat, measuring the average kinetic energy of molecules in a substance.

2. During change of state:

(i) Is there a rise in temperature of the material on heating it?

Ans: Yes there will be rise in the temperature of the material on heating.

(ii) What happens to the heat we supply?

Ans: As when the state is changed to the other state the molecules in it will have more kinetic energy as compared to previous.

3. Name the factors on which the thermal expansion of a wire depends.

Ans: The rise in temperature – The amount by which temperature increases influence the amount of expansion taking place. Nature of the material – Thermal expansion also depends upon the material of the solid being considered. Also, the thermal (heat) properties of the solid play an important role.

4. Give any two uses of a bimetallic strip.

Ans: There are two different elements in a bimetallic strip. This bimetallic strip is used in the displacement changes by mechanical stretch.These two elements have different temperatures.

5. If you have a uncalibrated mercury thermometer how will you calibrate it into a

(a) celsius thermometer.

(b) fahrenheit thermometer.

Ans: Here present a bulb in the thermometer which get equilibrium at standard temperature when it is kept in the water or ice try to make it in equilibrium. There is a difference between the Celsius and Fahrenheit thermometer as the Fahrenheit thermometer is more superior.

6. Explain the following:

(i) Why is mercury used as a thermometric liquid?

Ans: Mercury has a lower freezing point ( – 39 ° C ) and a high boiling point ( 356 . 7 ° C ) which makes it very suitable to measure higher temperatures. It is opaque and available in a pure state. It is a shiny liquid metal, hence can be easily seen through the glass of the thermometer tube.

(ii) Why does a bimetallic strip bend on heating?

Ans: Bimetallic strip consists of a strip of two different metals welded together. When we heat it, different metals expand by different amounts. It bends due to thermal expansion. Thermal expansion is the tendency of matter to change in shape, area, and volume in response to a change in temperature.

(iii) Why does steam at 100°C give more severe burns than water at 100°C?

Ans: Because of the latent heat at 100℃ of steam is more than the water so this is more severe than the water at 100℃.

(iv) Why do we use ice for cooling our drinks and not water at 0°C.?

Ans: Ice at zero degree centigrade has a greater cooling effect than water at 0 ∘ C because Ice it has low specific heat which means it stores less heat inside it.

7. Why is the heat given at the time of change of state called latent heat?

Ans: Because this energy enters or leaves a system during a phase change without causing a temperature change in the system, it is known as latent heat (latent means hidden).

8. A certain amount of water is heated at a constant rate. The time to bring it to boiling is t1 and the time required from beginning of boiling to boiling off the whole amount is t2. Which is greater t1or t2? Why?

Ans: We all know that time in heating the object at a certain temperature at starting is law as compared to the final temperature where the liquid gets boiled.

9. At what temperature the numerical value of temperature on fahrenheit scale will be double the value on celsius scale.

Ans: We know, C/5 = F-32/9.

Let, c = x  and  F = 2x,

So, x/5 = 2x -32/9;

Or, x = 160℃.

10. A 50 cm silver bar shortens by 1.0 mm when cooled. How much was it cooled? (Given: Coefficient of linear expansion of silver = 18 × 10-6 per degree celsius).

Ans: Do yourself.

11. How much heat energy is required to change 200 g of ice at – 20°C to water at 70°C? (Given: Latent heat of fusion of ice = 335 kJ kg–1, and specific heat of ice = 2100 J kg–1 °C–1, specific heat of water = 4.2 kJ kg–1 °C–1).

Ans: Do yourself.

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