CBSE Class 10 Physics Revision Assignment Set A

SOURCE OF ENERGY

TOPIC- NON- CONVENTIONAL SOURCE OF ENERGY

Solar Energy Solar energy

• Light energy and heat energy from the sun are known as solar energy.
• Sun has been radiating energy from the past 5 billion years and will continue to do so at the same rate for another 5 billion years or more.
• We must find ways to harness the energy with maximum efficiency, although only a small fraction of the solar energy reaches the earth’s surface.

Solar cooker
• Solar cookers and water heaters use solar energy to operate.
• Black surfaces absorb more energy than other surfaces and solar cookers use this property by coating their insides black.
• They use reflecting surfaces like mirrors to focus the sun’s rays.
• The device is covered with a glass plate thereby establishing the greenhouse effect by trapping heat inside the cooker.

Solar cell
• A device that converts solar energy into electricity is known as a solar cell.
• A typical solar cell produces a voltage of 0.5 1 V and 0.7 W of electrical power. A large number of such cells can combine to form a solar panel which can generate power large enough for practical uses.
• Advantages: (i) no moving parts (ii) require little maintenance (iii) can be set up in remote areas without the hassle and expenses of transmission lines.
• Disadvantages: (i) Requires a special grade silicon which is not easily available (ii) Usage of silver for interconnections makes it expensive.
• Uses: traffic signals, calculators, artificial satellites and space probes.

Energy From the Sea

Energy from sea

The seas and oceans and other water bodies are a source of kinetic and potential energy due to the immense volume of water and the motion of waves.

Tidal energy
• Tides are variations in the level of water due to the gravitational pull of the moon.
• The phenomenon of rise and fall of water level or high and low tide gives tidal energy.
• Tidal energy is obtained by constructing dams near the narrow openings of the sea. When the tide sets in, it moves the turbine which directly produces electricity.
• It is limited to places near the sea.

Wave energy
• Waves possess a lot of kinetic energy that can be harnessed to produce electricity.
• Waves are produced by strong winds blowing over the sea.
• Limited to places with strong winds. Devices have been designed to capture this energy.

Ocean thermal energy
• The difference in surface temperatures of water and water at a certain depth in oceans is exploited to harness this form of energy.
• Temperature difference must be 20∘between the surface and water up to depths of 2 km.
• Warm water is used to boil volatile ammonia to form vapours that move the turbine. Cold water is used to condense the vapour back to liquid.

Geothermal Energy Geothermal energy
• There is a huge amount of heat trapped inside the earth. Molten rocks from Earth’s core sometimes come up due to geological changes and get trapped in hotspots. Harnessing this heat energy is called geothermal energy.
• Any underground water present gets heated due to the hotspots and gets converted to steam which escapes from the surface of the earth as hot springs.
• This steam is used to rotate turbines and generate electricity.

Nuclear Energy

Nuclear energy
• Nuclear energy can be used to generate electricity by means of nuclear fission.
• In a nuclear reactor, the nuclear fuel is used to carry out sustained fission chain reaction to produce electricity at a controlled rate.

Nuclear fission

Nuclear fission is the process where a heavy atom (uranium or plutonium) is bombarded with neutrons that split the atom to give lighter nuclei. This process releases tremendous amounts of energy. For example, Fission of 1 atom of uranium gives 10 million times the energy of combustion of 1 atom of carbon from coal.

Disadvantages of using nuclear energy
• Nuclear waste is hazardous as heavy atoms decay into harmful subatomic particles.
• High setup and maintenance cost
• Limited availability of uranium
• Can be used for destructive purposes Nuclear fusion
• Fusion means combining lighter nuclei to produce a heavier nucleus, usually hydrogen or hydrogen isotopes to create helium.
• It releases a huge amount of energy. The mass deficit between the product and reactants are given by Einstein’s equation. E=mc²

QUESTIONS BASED ON ABOVE TOPICS :-

Question. Why a solar cooker painted black form outside?
Answer. Black surface absorbs more heat as compared to white or reflecting surface under identical conditions.

Question. List two non-conventional sources of energy.
Answer. Geothermal, solar, biomass, water, wind are the non-conventional sources of energy, (any two)

Question. Name two forms of energy in which solar energy manifests itself in oceAnswer.
Answer. The two forms of energy are Tidal energy and Ocean thermal energy.

Question. Name the nuclear process that is responsible for energy release on i. Sun. Ii. Nuclear reactor.
Answer. The nuclear process that is responsible for energy release are i. Nuclear fusion. Ii. Nuclear fission

Question. Name two materials used for fabricating solar cells. Answer. Silicon (Si) and germanium (Ge) are used for fabricating solar cells. Q6.Give one constructive and destructive use of Nuclear power.
Answer. Constructive use – Nuclear reactor for power generation. Destructive use - Atom bomb and Hydrogen bomb

Question. Which metal is used to connect various solar cells?
Answer. Silver metal is used to connect various solar cells.

Question. The mass number of three elements areA,B and C 2, 180 and 240. Which one of them is suitable for make a Hydrogen bomb.
Answer. Hydrogen bomb is based on nuclear fusion reaction, which is occur due to the fusion of light elements. Among all of them Element A is lighter. So element A is used to make a Hydrogen bomb.

Question. What is geothermal energy? How is it formed/found?
Answer. The energy obtained from hot molten rocks and hot fluid trapped inside the earth is called geothermal energy. 1. Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called hot spots. 2. When underground water comes in contact with the hot spot, steam is generated. 3. Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs. 4. The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity.

Question. Why is there a need for harnessing non conventional source of energy
Answer. The two main reasons to harness non-conventional sources of energy are:
(i) The population of the world is increasing at a very rapid rate due to which demands for energy is increasing day by day. As, fossil fuels like coal, petroleum, are present in a limited amount which and are likely to finish one day so the need for alternative sources of energy is essential.
(ii) Use of conventional sources of energy (coal, petroleum etc.) causes pollution. To reduce pollution use of non-conventional sources of energy is essential.

Question. How can energy be harnessed from the sea in different ways?
Answer. Two different ways of harnessing energy from ocean are:
1.Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.
2. Ocean thermal energy: The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean-thermal-energy conversion plants. These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 20 K (20°C) or more. The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator. The cold water from the depth of the ocean is pumped up and condense vapour again to liquid.

Home work Questions:-

1. Why is the solar cooker box covered with a plane glass plate?

2. Explain the term Hotspots in the context of geothermal energy production.
Differentiate between renewable and non – renewable sources of energy with one example for each.20 votes
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3. Differentiate between renewable and non – renewable sources of energy with one example for each.

Question. Explain with the help of labelled diagram the process of production of biogas in a biogas plant.
Answer.
• Biogas or gobar gas is a combustible gas.
• It is produced through the anaerobic breakdown of waste biomass.
• The biogas plant consists of the following parts:- 1) Inlet or charge pit:- for passage of slurry into the digester. The raw material used is cattle dung, farm refuse, organic waste.
2) Digester:- cylindrical tank which is airtight, above which is present a floating gas holder of metal with an outlet of gas and pit for removal of sludge.
• Here the organic wastes get solubilized into simpler substances called monomers (solubilisation).
• Monomers change to organic acid by fermenting microbes (abiogenesis).
• Organic acid mostly formed is acetic acid.
• Methanogens become active and act on components of microbial digestion and form methane gas (methanogens).
• Outlet:- consists of sludge which is used as manure.
• The methane gas formed in this process is used for cooking and lighting.

Question. Compare the advantages of generating energy from bio – mass than getting it from hydro power plant.
Answer. Biogas plant can be set up anywhere while hydropower plants can be set up in limited places only. biomass is 100% eco friendly. on the other hand, hydro power plant needs to destroy huge ecosystems while being set up. so biomass is better than hydropower.

Q1. Define and give units for each of the following:

a) Electric current
b) Potential difference
c) Resistance
d) Resistivity
e) Work done
f) Electric power.

Q2. State Ohms Law. How can it be verified experimentally? Does it hold good under all conditions? Is it a Universal law? Comment.

Q3. Two lamps one rated 60W at 220V and the other 40W at 220V are connected in parallel to the electric supply at 220V.
a) Draw a circuit diagram to show the connections.
b) Calculate the current drawn from the electric supply.
c) Calculate the total energy consumed by two lamps together when they operate for one hour.

Q4. What will happen when
a) Voltmeter is connected in series?
b) Ammeter is connected in parallel?
c) A parallel combination of two equal resistors is connected in series with a third resistor of resistance of 4 ohm if the combined resistance of three resistors is 5 ohm, find the resistance of the resistor in parallel combination .If a current of 2A is flowing through 4 ohm resistor, find the voltage across each of the parallel resistors.

Q5. With the help of a labelled circuit diagram illustrate the pattern of the field lines around
a) A current carrying straight long conducting wire.
b) A current carrying circular loop
c) A solenoid.

Q6. Describe the activity that shows that a current carrying conductor experiences a force perpendicular to its length and the external magnetic field. How does the flemings rule help us to find the direction of force. Explain.

Q7. Explain the phenomenon of electromagnetic induction. Describe an experiment for the same.

Q8. Draws a schematic labelled diagram of a domestic wire circuit which includes

a) Main fuse
b) Power meter
c) One light point
d) A fan
e) Power Plug.

Q9. Name the factors which affect the force on a current carrying conductor placed in magnetic field. Also mention how these factors depend upon them.

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