GSEB Solutions for Class 8 Science and Technology – Types of Energy (English Medium)
GSEB SolutionsMathsScience
Exercise 49:
Solution 1(a):
Renewable source of energy | Non-renewable source of energy |
The sources of energy which are continuously produced in nature and will never get exhausted are called renewable sources of energy. | The sources of energy which have accumulated over a very long period of time and cannot be replaced when exhausted are called non-renewable source of energy. |
These sources of energy will never get exhausted, so they are known as inexhaustible sources of energy. | These sources of energy will get exhausted some day, so they are known as exhaustible sources of energy. |
These sources of energy can be used endlessly, again and again. | Once exhausted, they will not be available to us again. |
Pollution is not caused by their use. | Pollution is caused by their use. |
Wind energy, solar energy, hydro energy, biomass energy are some examples of renewable sources of energy. | Fossil fuels like coal, petroleum, natural gas and nuclear fuels are some examples of non-renewable sources of energy. |
Exercise 50:
Solution 1(a):
Toys with a key have a spiral spring. On winding the key, it coils and compresses forcibly. The energy used by us for winding the spring is stored in the form of potential energy. Thus, the compressed spring possesses potential energy. When the spring begins to unwind to come back to its original position, its potential energy gets converted into kinetic energy. This kinetic energy drives the toy and it starts moving.
Solution 1(b):
Following are the objects which possess potential energy:
- A stretched rubber band
- Water stored in dam
- A stretched string of a bow
- A compressed spring
- The pressure in an un-opened soda bottle
- A car which is parked at the top of a hill
Exercise 51:
Solution 1(a):
A bullet fired from a gun possesses kinetic energy. Also, it moves with a very high speed due to which its kinetic energy increases. Thus, when the bullet collides with the surface of wood it can penetrate through it.
Solution 1(b):
During floods water in rivers flows with a high speed. The flowing water possesses higher kinetic energy due to its high speed. Thus, the flowing water carries whatever comes in its path. Hence, things are dragged along with the flow of water during floods.
Exercise 52:
Solution 1(a):
Heat energy is used for the following purposes:
- It is used for cooking food.
- Heat energy is used to warm the surroundings.
- It is in many power plants to generate electricity.
- It is also used to dry food grains and clothes.
- Heat energy is used to melt metals in furnaces for purification.
- It is used to heat water.
- Heat energy is used to run steam engines.
- It is required for various chemical reactions.
Exercise 53:
Solution 1(a):
Light energy is used for the following purposes:
- It is used by plants to prepare their food (photosynthesis).
- Light energy is used in a solar cooker, in which the light energy of the Sun is converted into heat energy.
- It is also used in solar cells which convert light energy from the Sun into electrical energy.
Solution 1(b):
When lime is added to water, a chemical reaction takes place and between the lime and water. The chemical energy stored in the lime transforms into heat energy. This makes the water hot and the glass feels warm when touched from outside.
Exercise 55:
Solution 1(a):
We know that when firecrackers are burst, a large sound is produced. This loud sound produces sound waves of high intensity. These sound waves collide with the vessels and produce vibrations in them. Hence, when fire crackers are burst, steel vessels in our houses vibrate and produce sound.
Solution 1(b):
The examples of sound energy are:
- The horn of a car
- Clapping your hands
- Thunder
- Buzzing of a bee
- Explosion of a firecracker
- Whistle of a train
Solution 1(c):
When a match-stick is burned with the help of a magnifying glass, the light energy of the Sun is transformed into heat energy.
Solution 1(d):
When an electric bulb is lighted with the help of a battery, the chemical energy of the battery gets converted into electrical energy. This electrical energy produced, gets converted to light energy and the bulb glows.
Exercise 57:
Solution 1(a):
Solution 1(b):
Exercise 57:
Solution 1(a):
The following steps should be taken to save energy in our everyday life:
- All electrical appliances like fans, lights, television, computer, etc. should be switched off when not in use.
- Energy efficient electrical devices should be used to save energy.
- Pulses and rice should be well soaked in water before cooking. This decreases the time of cooking.
- Food should be cooked in a pressure cooker whenever possible, as it takes less time and saves fuel.
- Refrigerator should not be opened frequently.
- Bicycle should be used to travel short distances. This will help save fuels like petrol. Also, public transport can be used instead of using private vehicles.
- All devices using petroleum products should be highly efficient in order to save energy.
- Use of solar devices should be encouraged.
Exercise 58:
Solution 1:
- Electrical energy is converted into light energy
- Chemical energy is converted into light energy
- Chemical energy is converted into light energy
- Chemical energy is converted into sound energy
- Kinetic energy is converted into mechanical energy
- Chemical energy is converted into heat energy
- Electrical energy is converted into heat energy
- Light energy is converted into chemical energy
Solution 2.1:
There is loss of energy in this case.
To avoid energy loss of energy, Kajal should do her homework during the day, in the presence of sunlight, so that it is not stressful.
Solution 2.2:
There is loss of energy in this case.
To avoid energy loss, all family members should share one or two televisions between themselves. This will help save electricity or electrical energy.
Solution 2.3:
There is no loss of energy in this case.
Solution 2.4:
There is loss of energy in this case.
The teachers should form groups and have car pools to travel to the school. This way they will save fuel.
Solution 2.5:
There is no loss of energy in this case.
Solution 2.6:
There is no loss of energy in this case.
Solution 3:
The measures to reduce energy loss are as follows:
- All electrical devices which are not in use should be switched off.
- Transportation vehicles should be serviced regularly.
- The stages of energy conversion from one form to another should be reduced as much as possible.
Solution 4:
Potential energy | Kinetic energy |
1. The energy possessed by an object due to its shape or specific position is called potential energy. | 1. The energy possessed by a body due to its motion is called kinetic energy. |
2. Work is said to be done only when potential energy is converted into kinetic energy. | 2. For work to be done by this energy, transformation of energy is not required. |
3. Potential energy of an object increases with an increase in the height of the object. | 3. Kinetic energy of a body increases with an increase in the motion of the body. |
4. Water stored in dam, stretched bow and a wound key toy are some examples of potential energy. | 4. Flowing water, released bow and a moving key toy are some examples of kinetic energy. |
Solution 5:
Law of conservation of energy: Energy can neither be converted nor destroyed; it is only converted from one form to another form. The total energy in the universe remains constant.
The law of conservation of energy can be seen in our everyday life.
For example, water stored in a dam is used to generate electricity. When water falls from a great height the potential energy stored in the water is converted into kinetic energy. This energy is used to rotate the turbine of a generator by converting the kinetic energy into mechanical energy. The generator converts the mechanical energy into electrical energy and electricity is produced. The electrical energy produced is used to switch on a bulb which gives light. In this way, electrical energy is converted into light energy.
Thus in the entire process, we see that energy is transformed from one form to another and that it is neither destroyed nor created.
Solution 6:
Five examples of energy transformations are as follows:
- When tube lights are switched on, electrical energy is transformed into light energy.
- In solar panels or solar cells, light energy gets transformed into electrical energy.
- When coal is burned, chemical energy of the coal gets transformed into heat energy.
- When we ring an electric door bell, electrical energy is transformed into sound energy.
- When a stone rolls down a mountain, potential energy is converted into kinetic energy.
Solution 7:
Most household appliances like, television, lights, washing machine, refrigerator, air conditioner, etc. run on electricity. Thus, we can say that we mainly use electrical energy
We get this energy form hydroelectric power stations, nuclear plants and thermal power plants.
Solution 8:
The energy obtained from the Sun is called solar energy. This energy is harnessed by using many different technologies. It is used in villages in the following ways:
- It is used for drying the harvested crop and food grains.
- In a solar cooker, solar energy is used to cook food.
- In a solar water heater, solar energy is used to heat water.