PHYSICS [3 Mark Question Answer]

The energy obtained from Sun is called solar energy.
A solar power plant is a device in which heat energy of sun is used to generate electricity. It consists of a large number of concave reflectors, at the focus of which there are black painted water pipes. The reflectors concentrate the heat energy of the sun rays on the pipes due to which water inside the pipes starts boiling and produces steam. The steam thus produced is used to rotate a steam turbine which drives a generator producing electricity.

Sun is the main source of energy on Earth.

Geothermal energy: The heat energy possessed by the rocks inside the Earth is called geothermal energy. The hot rocks present at the hot spots deep inside the Earth, heat the underground water and turn it into steam. This steam is compressed at high pressure between the rocks. Holes are drilled deep into the Earth up to the hot spots to extract the steam through pipes, which is utilized to rotate the turbines connected to the armature of an electric generator to produce electricity.

Ocean energy: Water in the oceans possesses energy in two forms:

1. Ocean thermal energy- The energy available due to the difference in temperature of water at the surface and at deeper levels of the ocean is called the ocean thermal energy. This energy is harnessed for producing electricity by a device called ocean thermal energy conversion power plant (OCTEC power plant).
2. Oceanic waves energy- The kinetic energy possessed by fast-moving oceanic (or sea) waves is called oceanic waves energy. Though models have been made to generate electricity from oceanic waves, but so far it has not been put to practical use.

Renewable:

1. Sun
2. Wind
3. Flowing water
4. Tides
5. Nuclear fuel

Non-renewable:

1. Coal
2. Petroleum
3. Natural gas

Renewable: The natural sources providing us energy continuously are called renewable sources of energy.
Non-renewable: The sources of energy that have accumulated in nature over a very long period of time and cannot be quickly replaced when exhausted are called non-renewable sources of energy.

Difference:

Renewable sources	Non-renewable sources
They can be utilised continuously.	They cannot be utilised once exhausted.
Examples: Sun, Wind	Example: Coal, Petroleum

Advantages of using nuclear energy:

1. A very small amount of nuclear fuel can produce a tremendous amount of energy.
2. Once the nuclear fuel is loaded into nuclear power plant, it continues to release energy for several years.

Disadvantages of using nuclear energy:

1. It is not a clean source of energy because very harmful nuclear radiations are produced in the process.
2. The waste causes environmental pollution.

Advantages of producing the hydro electricity:

1. It does not produce any environmental pollution.
2. It is a renewable source of energy.

Disadvantages of producing hydroelectricity:

1. Due to the construction of dams over the rivers, plants and animals of that place get destroyed or killed.
2. The ecological balance in the downstream areas of rivers gets disturbed.

The kinetic energy possessed by flowing water is called the water or hydro energy.
Principle of a hydroelectric power plant is that the water flowing in high altitude rivers is collected in a high dam (or reservoir). The water from the dam is then allowed to fall on a water turbine which is located near the bottom of the dam. The shaft of the turbine is connected to the armature of an electric generator or dynamo.
At present only 23% of the total electricity is generated by the hydro energy.

The laws of thermodynamics govern the energy flow in the ecosystem.
According to the first law of thermodynamic, the energy can be transformed from one form to the other form, but it can neither be created nor destroyed.
According to the second law of thermodynamics, when energy is put to work, a part of it is always converted in un-useful form such as heat mainly due to friction and radiation.

A food chain shows the feeding relationship between different living things in a particular environment or habitat. Often, a plant will begin a food chain because it can make its own food using energy from the Sun. In addition, a food chain represents a series of events in which food and energy are transferred from one organism in an ecosystem to another. Food chains show how energy is passed from the sun to producers, from producers to consumers, and from consumers to decomposers.

The role of a decomposer is to break down dead organisms and then feed on them. The nutrients created by the dead organisms are returned to the soil to be later used by the producers. Once these deceased organisms are returned to the soil, they are used as food by bacteria and fungi by transforming the complex organic materials into simpler nutrients. The simpler products can then be used by producers to restart the cycle. These decomposers play an important role in every ecosystem.

An ecosystem is defined as a self contained unit of living things and non living things. An ecosystem required Sunlight to maintain its working. The two main components of an ecosystem are following :
1. Abiotic component: It includes all the non-living components such as soll, water, air temperature, rocks, etc.

2. Biotic component: It includes all living components. All flora and fauna comes under biotic components.

The energy flow in ecosystem is linear i.e., it moves in a fixed direction. The solar energy is absorbed by plants and a part of it is converted into food. These plants (or primary producers) are then eaten by the primary consumers, which are consumed by secondary consumers and the secondary by tertiary consumers. This cycle is unidirectional. The dead and decomposed are fed by decomposers, which return the nutrients to the soil. At the end, the energy reaches the degraded state. It does not return to the sun to make the process cyclic, thus energy flow is linear.

When a given mass of water is heated from 0°C to 4°C, it contracts, i.e. its volume decreases.
On heating from 4°C to 10°C, it expands, i.e. its volume increases.