Class 8th Science Chapter 9 Sources and Effects of Heat Energy

Class 8th Science Chapter 9 Sources and Effects of Heat Energy

Class 8th Science Chapter 9 Sources and Effects of Heat Energy. Heat is a form of energy that is transferred from a substance that has a higher temperature to a substance that has a lower temperature. Adding heat to a substance increases its internal temperature. Heat is defined as the net amount of thermal energy in a system.

Class 8th Science Chapter 9 Sources and Effects of Heat Energy
Class 8th Science Chapter 9 Sources and Effects of Heat Energy

Class 8th Science Chapter 9 Sources and Effects of Heat Energy

Thermal energy is produced due to the movement of subatomic particles such as atoms, ions, and molecules to solids, gases, and liquids. Heat transfer occurs from one system to another due to the difference in temperature between the two systems. Class 8th Science Chapter 9 Sources and Effects of Heat Energy.

Class 8th Science Chapter 9 Sources and Effects of Heat Energy
Class 8th Science Chapter 9 Sources and Effects of Heat Energy

Class 8th Science Chapter 9 Sources and Effects of Heat Energy

The image will be loaded All forms of matter contain thermal energy. It doesn’t matter if it is a volcano or an ice cube, it has a certain amount of heat. Heat sources There are different forms of energy in nature such as mechanical energy, sound energy, light energy, electrical energy, tidal energy, thermal energy, etc. Thermal energy is generated due to the transfer of heat from a warm system to a cold system. Class 8th Science Chapter 9 Sources and Effects of Heat Energy. Thermal energy is an essential form of energy in our daily activities such as cooking, heating, ironing, etc. An object or system from which thermal energy is derived is called a thermal energy sources.

UNIT:9

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Q1. Define heat. What units are used for its measurement?

Ans. Heat is the flow of energy from a warm object to a cooler object.

Units of heat: Heat is measured in joules, BTU, and in calories.

Q2. Explain the peculiar behavior of water.

Ans. Liquids expands on heating but water contracts when it is heated from 00C to 40C. This peculiar behavior of water.

Q3. Which component expands on heating in fire alarms and how it works?

Ans. Brass and iron strips expand on heating in fire alarms. The bimetallic strip bends and touches the screw, which completes the circuit and the bell rings.

Q4. Describe the source and effects of heat.

Ans. Sources of heat

Sun, fire, friction, electricity and chemical reactions are some of the sources of heat.

Effects of heat: Changes the state of matter and chemicals, expands matter, increase temperature, form wind, rain and waves.

Q5. How Fahrenheit scale is different from Centigrade or Celsius scale?

Ans. Celsius has 100 degrees between the freezing and boiling point, while Fahrenheit has 180 degrees between these two points.

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Q1. Explain thermal expansion of solids with the help of an activity.

Ans. Thermal expansion of solids occurs in two ways i.e. linear expansion and volumetric expansion.

Linear expansion: It is the expansion in the length of solids due to heating.

Volumetric expansion: It is the expansion in the volume of solids due to heating.

Activity: Take a metallic sphere, which can pass easily through a ring. Heat the ring and pass it again through the ring again. Now, the sphere does not pass through the ring because heat has increased the volume of the sphere.

Q2. Describe the uses of expansion and contraction of liquids in our daily lives.

Ans. Expansion and contraction of heat has lots of uses in our daily lives.

Due to the peculiar behavior of water after 40C, aquatic life survives in the water below the surface of ice because ice acts as an insulator.

Mercury in thermometer expands due to heat and show the temperature of body.

Q3. Give reasons for the following questions.

  1. Why sag is given in the telephone or electrical wire?

Ans: Sag is given in the telephone or electrical wire so that they can contract in winter without breaking.

(b). Why mercury is preferred over alcohol in clinical thermometer?

Ans. Alcohol’s low boiling point cannot measure high temperature. Mercury’s high boiling point makes it suitable for thermometer.

(c) Why railway tracks are laid in sections with gaps between them?

Ans: Gaps between the railway tracks prevent them from bending due heat in summer.

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