grade 8 cbse sources of energy and area
Answers
Answer:
Explanation:
Introduction
We use various materials for our basic needs. Some of them are found in nature and some have been made by human efforts.
Natural resourcesDefinitionThe sources which are obtained from nature are called natural resources.Types of natural resources
1. Inexhaustible natural resources These sources are present in unlimited quantity in nature and are not likely to be exhausted by human activities. Examples: Sunlight, air, etc.
2. Exhaustible natural resources The amount of these resources in nature is limited, they can be exhausted by human activities. Examples: Forests, coal, petroleum. minerals, wild life, natural gas, etc.
Booster 1
Can sunlight get exhausted by human activities?ExplanationSunlight is an ultimate source of energy available free of cost. It cannot be exhausted by human activities as it is produced by a natural process of fusion inside the sun. Due to this nuclear fusion extremely large amount of energy is produced which comes in the form of sunlight.
Test Yourself
1. Name some inexhaustible substances other than sunlight and air.
2. Which fuel is used for running vehicles?
(a) Wood(b) Coal (c) Diesel(d) Charcoal
3. Which of the following is a natural resource?
(a) Tea(b) Cooked food (c) Air(d) Toffee
4. inexhaustible natural resource in nature are
(a) limited(b) unlimited (c) scarce(d) not present
5. Which of the following is an exhaustible natural resource?
(a) Air(b) Water (c) Soil(d) Forest
Types of natural resourcesMemory map
FuelsA fuel is a substance, which bums In air to produce energy without releasing harmful gases in large quantities.Fuels can be classified as natural (primary) fuels and derived (secondary) fuels. If a fuel Is present in its natural state, it is called natural fuel. If a fuel is processed to improve its quality, it Is called derived fuel.
Memory map
Calorific value of a fuel
Calorific value of a fuel is the amount of heat liberated by complete burning of a unit mass or volume of a fuel. For liquid or gaseous fuels, volume of fuel is considered while for solid fuels mass of fuel is considered to find out the calorific value.
Characteristics of an ideal fuel
(1) It should have a high calorific value.(2) It should not cause any pollution or should not produce harmful gases on combustion.(3) It should be of low cost and easily available.(4) It should be easy to handle, store and transport.(5) It should have moderate ignition temperature.(6) It should have moderate rate of combustion.