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Practice Class 10 Science MCQs on Convex Lens Power, Saturated Hydrocarbons, Electromagnetic Induction, Reflex Action, and Atmosphere Layers.
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Q1. What is the power of a convex lens of focal length 0.5 m?
Correct Answer: +2 D
Detailed Explanation
The power of a lens is calculated using the formula:
Here, the focal length (f) = 0.5 m.
Therefore, P = 1/0.5 = +2 D.
Since a convex lens is a converging lens, its power is always positive. The unit of power is Dioptre (D).
Important NCERT Points
- Power of a lens is the reciprocal of focal length.
- SI unit of power is Dioptre (D).
- Convex lenses have positive power.
- Concave lenses have negative power.
Exam-Oriented Fact
If focal length is given in centimeters, convert it into meters before calculating power.
Quick Revision Line
A convex lens of focal length 0.5 m has a power of +2 D.
Q2. Which of the following is a saturated hydrocarbon?
Correct Answer: Ethane
Detailed Explanation
Saturated hydrocarbons contain only single covalent bonds between carbon atoms. Ethane (C₂H₆) is an alkane and therefore a saturated hydrocarbon. Ethene and Ethyne contain double and triple bonds respectively, making them unsaturated hydrocarbons.
Important NCERT Points
- Alkanes are saturated hydrocarbons.
- Ethane belongs to the alkane family.
- Saturated hydrocarbons contain only single bonds.
- Unsaturated hydrocarbons contain double or triple bonds.
Exam-Oriented Fact
Methane, Ethane, and Propane are common examples of saturated hydrocarbons.
Quick Revision Line
Ethane is a saturated hydrocarbon containing only single bonds.
Q3. The phenomenon of electromagnetic induction is:
Correct Answer: Producing induced current in a coil
Detailed Explanation
Electromagnetic induction is the process of generating electric current in a conductor by changing the magnetic field around it. This phenomenon was discovered by Michael Faraday. It forms the working principle of electric generators and transformers.
Important NCERT Points
- Electromagnetic induction was discovered by Faraday.
- A changing magnetic field induces current.
- It is the basis of electric generators.
- Mechanical energy can be converted into electrical energy.
Exam-Oriented Fact
Faraday’s experiments established the principle of electromagnetic induction in 1831.
Quick Revision Line
Electromagnetic induction produces induced current due to a changing magnetic field.
Q4. Which of the following is an example of a reflex action?
Correct Answer: Blinking of eyes
Detailed Explanation
Reflex actions are quick, automatic, and involuntary responses to a stimulus. Blinking of eyes protects the eyes from dust, bright light, and injury. These actions occur without conscious thought and are controlled through reflex pathways.
Important NCERT Points
- Reflex actions are rapid and automatic.
- They help protect the body from harm.
- Reflex actions do not require conscious thinking.
- The nervous system coordinates reflex responses.
Exam-Oriented Fact
Touching a hot object and immediately withdrawing the hand is another common reflex action.
Quick Revision Line
Blinking of eyes is a protective reflex action.
Q5. Our atmosphere is divided into how many layers?
Correct Answer: 5
Detailed Explanation
The Earth’s atmosphere is commonly divided into five major layers based on temperature changes. These are the Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. Each layer has distinct characteristics and plays an important role in supporting life and protecting Earth.
Important NCERT Points
- The atmosphere has five main layers.
- Weather phenomena occur in the Troposphere.
- The ozone layer is present in the Stratosphere.
- The Exosphere is the outermost layer.
Exam-Oriented Fact
Most aircraft fly in the lower Stratosphere because weather disturbances are minimal there.
Quick Revision Line
The Earth’s atmosphere is divided into five major layers.
One-Line Revision Sheet
- A convex lens of focal length 0.5 m has a power of +2 D.
- Ethane is a saturated hydrocarbon.
- Electromagnetic induction produces induced current in a conductor.
- Blinking of eyes is a reflex action.
- The atmosphere consists of five major layers.
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