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Class 10 Science MCQs on electrical energy, global warming, concave mirrors, blood pressure, fossil fuels, and environmental science with detailed explanations.
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Q1. What is the value of 1 kWh in Joules?
Correct Answer: 3.6 × 10⁶ Joules
Detailed Explanation:
A kilowatt-hour (kWh) is a commercial unit of electrical energy that is widely used to measure electricity consumption in homes, schools, offices, and industries. One kilowatt means 1000 watts of power, and one hour contains 3600 seconds. Electrical energy is calculated by multiplying power by time.
Therefore:
1 kWh = 1000 watts × 3600 seconds
= 3,600,000 Joules
= 3.6 × 10⁶ Joules
This means that if an electrical appliance with a power rating of 1000 watts runs continuously for one hour, it consumes 1 kWh of energy. Electricity companies use kilowatt-hours, commonly called “units,” to calculate electricity bills.
The Joule is the SI unit of energy, while the kilowatt-hour is a practical unit used for large-scale energy measurement. Understanding this conversion helps students solve numerical problems related to electricity consumption and power calculations. Questions based on the relationship between kilowatt-hours and Joules are frequently asked in Class 10 board examinations and competitive tests.
Real-Life Examples:
- A 1000-watt electric heater used for one hour consumes 1 kWh of energy.
- A 1000-watt electric iron running for two hours consumes 2 kWh of energy.
- Household electricity bills are calculated in kilowatt-hours.
Important NCERT Points:
- Joule is the SI unit of energy.
- Kilowatt-hour is the commercial unit of electrical energy.
- 1 kWh = 3.6 × 10⁶ Joules.
- Electrical energy consumption is measured using an energy meter.
Exam-Oriented Fact:
One unit of electricity is equal to one kilowatt-hour.
Quick Revision Line:
1 kWh = 3.6 × 10⁶ Joules.
Q2. Which gas is responsible for global warming?
Correct Answer: Carbon dioxide (CO₂)
Detailed Explanation:
Global warming refers to the gradual increase in the average temperature of the Earth due to the excessive accumulation of greenhouse gases in the atmosphere. Among these gases, Carbon dioxide (CO₂) is considered the most important contributor because it is released in very large quantities through human activities.
The major sources of Carbon dioxide (CO₂) include the burning of fossil fuels such as coal, petroleum, and natural gas. Vehicles, factories, thermal power plants, and industrial processes continuously release Carbon dioxide (CO₂) into the atmosphere. Deforestation further increases the problem because trees absorb Carbon dioxide (CO₂) during photosynthesis.
Carbon dioxide (CO₂) traps heat reflected from the Earth’s surface and prevents it from escaping into space. This process is known as the greenhouse effect. While a natural greenhouse effect is necessary to maintain suitable temperatures on Earth, excessive Carbon dioxide (CO₂) strengthens this effect and causes global warming.
Global warming leads to melting glaciers, rising sea levels, heat waves, floods, droughts, and climate change. Reducing fossil fuel consumption, increasing renewable energy use, and planting more trees can help lower Carbon dioxide (CO₂) levels and reduce global warming.
Real-Life Examples:
- Vehicle exhaust releases Carbon dioxide (CO₂).
- Coal-based thermal power plants emit large amounts of Carbon dioxide (CO₂).
- Deforestation reduces the natural absorption of Carbon dioxide (CO₂).
Important NCERT Points:
- Carbon dioxide (CO₂) is a major greenhouse gas.
- Greenhouse gases trap heat in the atmosphere.
- Deforestation increases Carbon dioxide (CO₂) concentration.
- Renewable energy sources help reduce greenhouse gas emissions.
Exam-Oriented Fact:
Carbon dioxide (CO₂) is the greenhouse gas most commonly associated with global warming in school examinations.
Quick Revision Line:
Carbon dioxide (CO₂) is the primary greenhouse gas responsible for global warming.
Q3. The image formed by a concave mirror is real, inverted, and of the same size as the object. The object is placed at:
Correct Answer: At Center of Curvature (C)
Detailed Explanation:
A concave mirror is a spherical mirror whose reflecting surface curves inward. The image formed by a concave mirror depends on the position of the object relative to the Focus (F) and the Center of Curvature (C).
When the object is placed exactly at the Center of Curvature (C), the reflected rays meet at the same point after reflection. As a result, the image is formed at the Center of Curvature (C) itself. The image produced is real, inverted, and exactly equal in size to the object.
This is one of the most important image-formation cases in the Class 10 Science syllabus. If the object is placed beyond the Center of Curvature (C), the image becomes smaller. If it is placed between the Focus (F) and the Center of Curvature (C), the image becomes larger. When the object is placed at the Focus (F), the image forms at infinity.
Students should learn standard ray diagrams carefully because they frequently appear in board examinations and objective questions.
Real-Life Examples:
- Reflecting telescopes use concave mirrors.
- Solar furnaces use concave mirrors to concentrate sunlight.
- Concave mirrors are used in scientific instruments.
Important NCERT Points:
- Object at Center of Curvature (C) forms image at Center of Curvature (C).
- The image is real and inverted.
- The image size is equal to the object size.
- Ray diagrams are important for examination preparation.
Exam-Oriented Fact:
If the image is real, inverted, and of the same size, the object is placed at the Center of Curvature (C).
Quick Revision Line:
Object at Center of Curvature (C) produces a real, inverted, and same-sized image.
Q4. The normal systolic blood pressure in humans is:
Correct Answer: 120 mm Hg
Detailed Explanation:
Blood pressure is the pressure exerted by circulating blood on the walls of arteries. It is one of the most important indicators of cardiovascular health and is measured using a sphygmomanometer.
A blood pressure reading consists of two values. The higher value is called systolic blood pressure, and the lower value is called diastolic blood pressure. Systolic blood pressure is recorded when the heart contracts and pumps blood into the arteries. Diastolic blood pressure is measured when the heart relaxes between two heartbeats.
For a healthy adult, the normal blood pressure is approximately 120 mm Hg / 80 mm Hg. Here, 120 mm Hg represents the systolic blood pressure, while 80 mm Hg represents the diastolic blood pressure.
Abnormally high blood pressure can increase the risk of heart disease, stroke, and kidney disorders. Maintaining a balanced diet, exercising regularly, avoiding excessive salt intake, and reducing stress help maintain healthy blood pressure levels.
Real-Life Examples:
- Doctors routinely measure blood pressure during medical check-ups.
- Blood pressure monitoring machines are used in hospitals and homes.
- Regular exercise helps maintain healthy blood pressure.
Important NCERT Points:
- Normal blood pressure is approximately 120 mm Hg / 80 mm Hg.
- Systolic blood pressure occurs during heart contraction.
- Diastolic blood pressure occurs during heart relaxation.
- Blood pressure reflects the health of the circulatory system.
Exam-Oriented Fact:
120 mm Hg is the normal systolic blood pressure of a healthy adult.
Quick Revision Line:
Normal systolic blood pressure in humans is 120 mm Hg.
Q5. Which of the following is not a fossil fuel?
Correct Answer: Wood
Detailed Explanation:
Fossil fuels are natural fuels formed from the remains of plants and animals that lived millions of years ago. Over long periods, heat and pressure transformed these remains into Coal, Petroleum, and Natural Gas.
Coal is mainly formed from ancient plant remains, while Petroleum and Natural Gas originate from marine organisms buried beneath sediments. Since these fuels take millions of years to form, they are classified as non-renewable resources.
Wood, however, is obtained directly from living trees and plants. Since trees can be replanted and grown again, wood is considered a renewable resource rather than a fossil fuel. Although wood can be used as fuel, its origin and formation process are completely different from fossil fuels.
The excessive use of fossil fuels increases Carbon dioxide (CO₂) emissions, leading to environmental problems such as air pollution and global warming. Therefore, there is a growing emphasis on renewable energy sources like solar energy, wind energy, and hydropower.
Real-Life Examples:
- Coal is used in thermal power stations.
- Petroleum is refined to produce petrol and diesel.
- Wood is commonly used as a traditional fuel in rural areas.
Important NCERT Points:
- Coal, Petroleum, and Natural Gas are fossil fuels.
- Fossil fuels are non-renewable resources.
- Wood is a renewable resource.
- Burning fossil fuels increases Carbon dioxide (CO₂) emissions.
Exam-Oriented Fact:
Wood is a renewable biomass fuel and is not classified as a fossil fuel.
Quick Revision Line:
Wood is a renewable resource, whereas Coal, Petroleum, and Natural Gas are fossil fuels.
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