CBSE Class 10 Science (2026–27)
Chapter 13: Sources of Energy
20 Important Questions & Answers
These answers are are based on the NCERT/CBSE syllabus covering renewable and non-renewable energy sources, fossil fuels, solar energy, wind energy, hydropower, biomass, and nuclear energy.
Q1. What is a source of energy? State any two characteristics of a good source of energy.
Answer:
A source of energy is any system or material from which useful energy can be obtained for performing work. Examples include coal, sunlight, wind, and flowing water. A good source of energy should possess several desirable characteristics. First, it should have a high calorific value so that a large amount of energy can be obtained from a small quantity of fuel. Second, it should be easy to store and transport so that it can be used conveniently at different places. In addition, a good source of energy should be economical, safe to use, and cause minimum environmental pollution. These qualities make an energy source suitable for large-scale use.
Q2. Why are fossil fuels considered non-renewable sources of energy?
Answer:
Fossil fuels such as coal, petroleum, and natural gas are called non-renewable sources of energy because they take millions of years to form from the remains of ancient plants and animals. Their rate of formation is extremely slow compared to the rate at which humans consume them. Once these fuels are exhausted, they cannot be replenished within a human lifetime. Continuous use of fossil fuels is reducing their reserves rapidly. Moreover, burning them releases harmful gases that contribute to air pollution and global warming. Therefore, fossil fuels are limited resources that must be used carefully and supplemented with alternative energy sources.
Q3. What are renewable sources of energy? Give two examples.
Answer:
Renewable sources of energy are those sources that are naturally replenished and can be used repeatedly without the risk of exhaustion. They are continuously available through natural processes and are considered environmentally friendly. Examples include solar energy and wind energy. Solar energy is obtained from the Sun and can be converted into electricity using solar cells. Wind energy is harnessed through wind turbines that convert the kinetic energy of moving air into electrical energy. Renewable sources help reduce dependence on fossil fuels and minimize environmental pollution. They are considered sustainable options for meeting future energy demands.
Q4. What are the disadvantages of using fossil fuels?
Answer:
Fossil fuels have several disadvantages despite being widely used. Their reserves are limited and may eventually get exhausted because they are non-renewable resources. Burning fossil fuels releases carbon dioxide, sulfur dioxide, and nitrogen oxides, which contribute to air pollution, acid rain, and global warming. Mining and extraction of these fuels can also damage ecosystems and landforms. Furthermore, dependence on fossil fuels creates energy security concerns as reserves become depleted. Therefore, excessive use of fossil fuels poses both environmental and economic challenges, making it important to develop cleaner and renewable alternatives for future energy needs.
Q5. What is a thermal power plant? Why are such plants generally located near coal reserves?
Answer:
A thermal power plant is a facility where fossil fuels such as coal, petroleum, or natural gas are burned to produce heat energy. This heat converts water into steam, which rotates turbines connected to generators for producing electricity. Thermal power plants are usually located near coal reserves because transporting large quantities of coal over long distances is expensive and inefficient. By establishing plants close to coal mines, transportation costs and energy losses can be minimized. Additionally, a continuous supply of fuel is ensured. This arrangement improves the efficiency and economic viability of electricity generation through thermal power plants.
Q6. Explain the working of a hydropower plant.
Answer:
A hydropower plant generates electricity by utilizing the potential energy of stored water. Water is collected behind a dam at a significant height. When released, the water flows through pipes at high speed and strikes the blades of turbines. The turbines begin to rotate, converting the kinetic energy of water into mechanical energy. These turbines are connected to generators that convert mechanical energy into electrical energy. Hydropower is considered a renewable source of energy because flowing water is continuously replenished through the water cycle. It is a clean source of energy, although large dams may affect local ecosystems and human settlements.
Q7. What is biomass? How is it useful as a source of energy?
Answer:
Biomass refers to organic matter obtained from plants, animals, agricultural waste, wood, and biodegradable materials. It serves as a renewable source of energy because it can be replenished through natural processes. Biomass can be burned directly to produce heat or converted into biogas through microbial decomposition in the absence of oxygen. The energy produced from biomass is useful for cooking, heating, and electricity generation. It also helps in waste management by utilizing agricultural and animal waste effectively. Since biomass absorbs carbon dioxide during growth, it is considered relatively environment-friendly compared to fossil fuels when managed sustainably.
Q8. What is biogas? Mention any two advantages of biogas.
Answer:
Biogas is a combustible fuel produced by the anaerobic decomposition of organic waste such as cattle dung, sewage, and plant residues. It mainly contains methane, carbon dioxide, and small amounts of other gases. One advantage of biogas is that it burns cleanly without producing smoke, reducing air pollution. Another advantage is that it provides an effective method for waste disposal while producing useful energy. The leftover slurry from biogas plants can also be used as a nutrient-rich manure for agriculture. Thus, biogas contributes to energy production, waste management, and environmental conservation simultaneously.
Q9. How is wind energy harnessed to produce electricity?
Answer:
Wind energy is harnessed using wind turbines installed in areas where strong and steady winds are available. When the wind blows, it causes the blades of the turbine to rotate. The rotating blades turn a shaft connected to a generator. The generator converts the mechanical energy of rotation into electrical energy. A large number of wind turbines are often grouped together to form wind farms, which can generate substantial amounts of electricity. Wind energy is renewable, non-polluting, and freely available. However, its effectiveness depends on wind speed and suitable geographical conditions for installation.
Q10. State two advantages and two limitations of wind energy.
Answer:
Wind energy offers several benefits. First, it is a renewable source of energy that does not get exhausted. Second, it does not produce harmful pollutants during electricity generation. However, wind energy also has limitations. One limitation is that wind does not blow continuously, making power generation unreliable at times. Another limitation is that large areas of land are required for installing wind farms. In addition, wind turbines can be noisy and may affect the local landscape. Despite these challenges, wind energy remains an important component of sustainable energy development worldwide.
Q11. What is solar energy? Why is it considered an ideal energy source?
Answer:
Solar energy is the energy obtained from the Sun in the form of heat and light. It is considered an ideal energy source because it is abundant, renewable, and available in most parts of the world. Solar energy does not produce air pollution or greenhouse gases during use, making it environmentally friendly. It can be harnessed using solar cells, solar cookers, and solar water heaters. Although the initial installation cost of solar devices may be high, their operating cost is low because sunlight is free. These advantages make solar energy an important solution for meeting future energy demands sustainably.
Q12. What are solar cells? Mention their uses.
Answer:
Solar cells, also known as photovoltaic cells, are devices that convert sunlight directly into electrical energy. They are usually made of semiconductor materials such as silicon. When sunlight falls on a solar cell, electrical energy is generated through the photovoltaic effect. Solar cells are used in calculators, street lights, satellites, traffic signals, and solar power plants. They are especially useful in remote areas where conventional electricity supply is difficult. Since solar cells operate without producing pollution and require little maintenance, they provide a reliable and sustainable source of electricity for various applications.
Q13. Why are solar cells not widely used everywhere?
Answer:
Despite their advantages, solar cells are not used everywhere due to certain limitations. The most important limitation is their high initial installation cost because semiconductor materials and associated equipment are expensive. Solar cells also depend on sunlight and cannot generate electricity effectively during cloudy weather or at night. Large areas are often required to install enough panels for significant power generation. Furthermore, energy storage systems such as batteries add to the overall cost. Although technological advancements are reducing these limitations, solar energy still faces challenges in becoming the sole source of electricity in many regions.
Q14. What is ocean thermal energy?
Answer:
Ocean thermal energy is a form of renewable energy obtained from the temperature difference between warm surface water and cold deep-sea water. In regions where this temperature difference is significant, the warm water is used to vaporize a liquid with a low boiling point. The vapor produced drives a turbine connected to a generator, producing electricity. Afterward, cold deep-sea water is used to condense the vapor back into liquid form. This process can be repeated continuously. Ocean thermal energy offers a renewable source of electricity, although its use is limited to suitable coastal regions with adequate temperature differences.
Q15. What is geothermal energy?
Answer:
Geothermal energy is the heat energy stored beneath the Earth’s surface. In certain regions, underground water comes into contact with hot rocks and turns into steam. This steam can be brought to the surface through wells and used to rotate turbines connected to generators for electricity production. Geothermal energy is renewable because heat is continuously generated within the Earth. It produces very little pollution and provides a steady supply of power. However, suitable geothermal sites are limited to specific regions where underground heat sources are accessible. This restricts its widespread use.
Q16. What is nuclear energy?
Answer:
Nuclear energy is the energy released during nuclear reactions, particularly nuclear fission. In nuclear power plants, atoms of radioactive elements such as uranium are split into smaller nuclei. This process releases a large amount of energy in the form of heat. The heat is used to produce steam, which drives turbines and generates electricity. Nuclear energy can produce enormous amounts of power from a small quantity of fuel. However, it has disadvantages such as the risk of radiation leaks and the challenge of safely disposing of radioactive waste. Therefore, strict safety measures are necessary in nuclear power generation.
Q17. Differentiate between renewable and non-renewable sources of energy.
Answer:
Renewable sources of energy are those that can be replenished naturally and used repeatedly. Examples include solar energy, wind energy, and hydropower. They are generally environment-friendly and sustainable. Non-renewable sources of energy, on the other hand, are limited in quantity and take millions of years to form. Examples include coal, petroleum, and natural gas. These sources get depleted with continuous use and often cause environmental pollution. Renewable energy helps reduce dependence on fossil fuels and promotes sustainable development, whereas non-renewable energy resources require careful conservation due to their limited availability.
Q18. Why is there a need to develop alternative sources of energy?
Answer:
There is an increasing need to develop alternative sources of energy because conventional fossil fuel reserves are limited and are being consumed rapidly. Their excessive use also leads to environmental problems such as air pollution, acid rain, and global warming. Alternative energy sources like solar, wind, geothermal, and tidal energy are renewable and cleaner. They help reduce greenhouse gas emissions and ensure long-term energy security. As energy demand continues to rise with population growth and industrial development, reliance solely on fossil fuels is unsustainable. Therefore, developing alternative sources is essential for meeting future energy needs while protecting the environment.
Q19. What are the environmental consequences of using fossil fuels?
Answer:
The use of fossil fuels has significant environmental consequences. Burning coal, petroleum, and natural gas releases carbon dioxide, which contributes to global warming and climate change. It also emits sulfur dioxide and nitrogen oxides that can cause acid rain. Air pollution from fossil fuel combustion affects human health by increasing respiratory diseases. Mining and drilling activities can damage ecosystems and contaminate water resources. Furthermore, fossil fuel extraction often leads to habitat destruction. Due to these adverse impacts, there is a growing emphasis on adopting cleaner and renewable energy sources to reduce environmental degradation and ensure sustainable development.
Q20. Why is energy conservation important?
Answer:
Energy conservation is important because many commonly used energy resources, especially fossil fuels, are limited and non-renewable. Conserving energy helps extend the availability of these resources for future generations. It also reduces environmental pollution and greenhouse gas emissions associated with energy production and consumption. Energy conservation can be achieved by using energy-efficient appliances, reducing wastage, and promoting renewable energy sources. Conserving energy lowers costs, improves energy security, and decreases dependence on imported fuels. Since global energy demand is continuously increasing, responsible use of available resources is essential for achieving sustainable development and protecting the environment.