CG Board Class 10 Science Chapter 18 Solutions: Energy: Forms and Sources (ऊर्जा: स्वरूप एवं स्रोत) (2026-27)

Answer: (c) Nuclear energy

Reason: Nuclear energy is obtained from the binding energy inside atomic nuclei through nuclear fission or fusion reactions, independent of solar radiation. Geothermal, wind, and biomass energy are indirectly driven by solar radiation.

Answer: (d) Methane, Carbon dioxide, Hydrogen

Reason: Biogas is produced by the anaerobic decomposition of organic matter and consists of methane (up to 75%), carbon dioxide, hydrogen, and hydrogen sulphide.

Answer: (b) Breaking of a heavy nucleus into light nuclei due to printing alignment, but the core textbook definition explicitly confirms option (b)).*

Reason: By textbook definition, nuclear fission is a nuclear reaction in which the nucleus of a heavy atom (such as Uranium, Plutonium) is split into lighter nuclei upon bombardment with low-energy neutrons.

Answer: (a) Coal, petroleum, natural gas

Reason: Fossil fuels are non-renewable energy resources formed inside the earth over millions of years from buried organic remains.

Answer: (c) Solar energy into electric energy

Reason: A solar cell directly converts solar radiation energy into electrical energy.

Answer: Rainy / Cloudy

Answer: Electrical and Light (or Light)

Answer: Tidal energy, Wave energy, Ocean thermal energy

Answer: Solar (Light) ; Thermal (Heat)

Answer:

Mechanism of Solar Cooker:

1. Construction: A solar cooker consists of an insulated outer box made of wood or metal. The inside walls and bottom of the box are painted black to absorb maximum solar thermal radiation. Food is placed inside dark-painted metal containers.
2. Glass Cover: The top of the box is covered with a transparent sheet glass. Once solar radiation enters through the glass cover, the glass sheet prevents the long-wave thermal heat rays from escaping, trapping the heat inside through the greenhouse effect.
3. Reflector Mirror: A plane mirror reflector is attached at the top lid to reflect additional sunbeams directly into the box.
4. Operation: Due to continuous heat trapping, the internal temperature rises to 100-140° C within 2-3 hours, which cooks food items like rice, pulses, and vegetables effectively.

`

[Sunlight]

/

\/ (Plane Mirror Reflector)

/ \______/

/ |

/ v (Glass Cover)

+————————+

| [Black Containers] | <-- Insulated Box

| (Food: Rice, Pulses) | (Inner walls painted black)

+————————+

`

Answer:

(i) Black surfaces are excellent absorbers of thermal radiation. Painting the interior black ensures maximum absorption of sunlight falling inside the box.

(ii) A glass sheet allows light rays to pass inside the cooker but stops thermal heat rays from trapped air inside from escaping out. This traps heat inside and builds up the temperature to 100-140° C.

(iii) A plane mirror acts as a reflector that redirects additional parallel rays of sunlight directly into the cooker box, increasing light concentration and heating efficiency.

Answer:

Solar Cell (or Solar Cell Panel).

Answer:

Apart from cattle-dung (gobar), crop residues remaining after harvesting, vegetable wastes, organic plant materials, domestic sewage, and poultry/animal waste can be put inside a biogas plant for anaerobic decomposition.

Answer:

Answer:

The classification of energy sources into renewable and non-renewable is based on their availability, rate of natural replenishment, and exhaustibility:

1. Renewable Energy Sources: Sources that are continuously regenerated by natural processes and will not run out over time (e.g., solar, wind, tidal, hydel energy).
2. Non-Renewable Energy Sources: Sources that have taken millions of years to form, exist in limited reserves, and get exhausted rapidly upon continuous use without quick replenishment (e.g., coal, petroleum, natural gas).

Answer:

Reason: Energy from the Sun is available naturally every day in abundant amounts and will not get exhausted for billions of years.

2. Wind Energy:

Reason: Wind currents are generated continuously due to solar heating of earth and atmospheric pressure differences, making wind a naturally self-replenishing source.

2. :

Answer:

1. Environment Friendly: Solar energy is clean and non-polluting; it produces no toxic gases or smoke.
2. Abundant and Free: India receives solar radiation for most parts of the year without cost.
3. Versatile Direct Conversion: Converts directly into electricity using solar cells with no moving mechanical parts, requiring low maintenance.
4. Remote Accessibility: Solar panels can be set up in far-off, remote, or hilly regions where laying electrical transmission lines is expensive.

Answer:

1. Minimum Wind Speed Requirement: Wind energy farms can only be established in areas where wind speed is consistently greater than 15 km/h to turn turbines efficiently.
2. Large Land Area Needed: Setting up a wind energy farm requires vast tracts of land.
3. High Capital Cost & Maintenance: Initial installation cost is very high, and exposed blades suffer high wear and tear from weather.
4. Intermittent Supply: Backup facilities are required when wind speeds fall below required limits during calm weather.

Answer:

Conversion of Energy:

Conversion of energy refers to the process of transforming energy from one form (such as chemical, potential, kinetic, or solar) into another usable form (such as electrical, thermal, light, or sound energy).

According to the Law of Conservation of Energy, energy can neither be created nor destroyed; it can only be transformed from one form to another, while the total energy of a closed system remains constant.