Strengthen your TNPSC Physics preparation with this TNPSC Physics Light Quiz, featuring important General Science questions on reflection, refraction, lenses, prisms, and atmospheric refraction. Each question is accompanied by clear answers and explanations to help you revise key concepts with confidence.
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TNPSC Physics Light Quiz 3 – Detailed Explanations
Go beyond the correct answers with detailed explanations designed for TNPSC Physics Light Quiz 3. Learn the essential TNPSC Physics and General Science concepts behind each question, helping you improve your understanding of light and perform better in the TNPSC exam.
1. When a ray of light passes from air into glass, it bends towards the normal because:
When light travels from a rarer medium like air into a denser medium such as glass, its speed decreases. This change in speed causes the light ray to bend towards the normal, a phenomenon known as refraction. The frequency of light remains constant, while its wavelength decreases inside the denser medium.
Key Points:
- Refraction occurs due to a change in the speed of light.
- Light bends towards the normal when entering a denser medium.
- Frequency remains unchanged during refraction.
- Wavelength decreases as the speed decreases.
Real-Life Example: Light entering a glass window or a water tank bends due to refraction.
Correct Answer: B. Its speed decreases
2. The ratio of the speed of light in vacuum to its speed in a medium is called:
The refractive index is a measure of how much light slows down when it enters a transparent medium. A higher refractive index means light travels more slowly in that material. This property helps determine how much light bends during refraction.
Key Points:
- Refractive index measures the optical density of a medium.
- It compares the speed of light in vacuum with its speed in a medium.
- A higher refractive index causes greater bending of light.
Real-Life Example: Diamonds have a high refractive index, giving them their brilliant sparkle.
Correct Answer: B. Refractive Index
3. Which lens is thicker at the centre than at the edges?
A convex lens is thicker at the centre and thinner at the edges. It bends parallel rays of light inward so that they meet at a point called the principal focus. Because of this property, it is also known as a converging lens.
Key Points:
- Convex lenses are thicker at the centre.
- They converge parallel light rays.
- They can produce both real and virtual images depending on the object’s position.
Real-Life Example: Convex lenses are used in cameras, microscopes, and magnifying glasses.
Correct Answer: C. Convex Lens
4. A convex lens is also known as a:
A convex lens is called a converging lens because it brings parallel rays of light together at the principal focus after refraction. This property makes it useful in many optical instruments that require image formation or magnification.
Key Points:
- Convex lenses converge light rays.
- Parallel rays meet at the principal focus.
- Used for image formation and magnification.
Real-Life Example: A camera lens focuses incoming light onto the image sensor using a convex lens.
Correct Answer: B. Converging Lens
5. Which lens is thinner at the centre than at the edges?
A concave lens is thinner at the centre and thicker at the edges. It spreads parallel rays of light outward after refraction, making it a diverging lens. The image formed is always virtual, erect, and smaller than the object.
Key Points:
- Concave lenses are thinner at the centre.
- They diverge parallel rays of light.
- They always form virtual, erect, and diminished images.
Real-Life Example: Concave lenses are commonly used in spectacles to correct short-sightedness (myopia).
Correct Answer: C. Concave Lens
6. A concave lens always forms an image that is:
A concave lens spreads light rays outward after refraction, making it a diverging lens. Since the rays do not actually meet, the image formed is always virtual, erect, and smaller than the object, regardless of the object’s position.
Key Points:
- A concave lens is a diverging lens.
- It always forms a virtual image.
- The image is erect and diminished.
- The image is formed on the same side of the lens as the object.
Real-Life Example: Concave lenses are used in spectacles to correct myopia (short-sightedness).
Correct Answer: B. Virtual, Erect and Diminished
7. Parallel rays of light passing through a convex lens meet at the:
A convex lens bends parallel rays of light inward until they meet at a fixed point called the principal focus. The distance between the optical centre and the principal focus is known as the focal length of the lens.
Key Points:
- A convex lens converges parallel light rays.
- The meeting point is called the principal focus.
- The focal length is measured from the optical centre to the principal focus.
Real-Life Example: A magnifying glass focuses sunlight onto a small spot at its principal focus.
Correct Answer: C. Principal Focus
8. The point through which a ray passes without deviation in a thin lens is called the:
The optical centre is the central point of a thin lens through which a light ray passes without changing its direction. This property simplifies ray diagrams and helps locate image positions accurately.
Key Points:
- A ray passing through the optical centre emerges undeviated.
- The optical centre lies on the principal axis.
- This rule is commonly used in lens ray diagrams.
Real-Life Example: Students use the optical centre rule while drawing image formation diagrams in Physics.
Correct Answer: B. Optical Centre
9. The straight line joining the optical centre and the principal foci is called the:
The principal axis is an imaginary straight line that passes through the optical centre and both principal foci of a lens. It serves as the reference line for drawing rays and determining image formation.
Key Points:
- The principal axis passes through the optical centre.
- It connects both principal foci.
- It is the reference line for ray diagrams.
Real-Life Example: In optical instruments, lenses are aligned along the principal axis for clear image formation.
Correct Answer: B. Principal Axis
10. Which lens is commonly used as a magnifying glass?
A magnifying glass uses a convex lens to produce a virtual, erect, and enlarged image when the object is placed within its focal length. This allows small objects to appear larger and more detailed.
Key Points:
- A magnifying glass uses a convex lens.
- The object must be placed within the focal length.
- The image formed is virtual, erect, and magnified.
Real-Life Example: Jewellers and watchmakers use magnifying glasses to inspect tiny details.
Correct Answer: B. Convex Lens
11. A pencil partially immersed in water appears bent due to:
When light travels from water to air, it changes speed and bends away from the normal. This bending of light, called refraction, makes the submerged part of the pencil appear shifted from its actual position, creating the illusion that the pencil is bent.
Key Points:
- Refraction occurs when light passes between different media.
- Light changes direction because its speed changes.
- The apparent position of an object differs from its actual position.
Real-Life Example: A spoon placed in a glass of water appears bent at the water’s surface due to refraction.
Correct Answer: B. Refraction
12. The apparent depth of water is less than the real depth because of:
Light rays from the bottom of a water body bend away from the normal as they move from water to air. As a result, the bottom appears closer to the surface than it actually is, making the apparent depth less than the real depth.
Key Points:
- Refraction makes underwater objects appear raised.
- Apparent depth is always less than the real depth.
- The effect occurs when light moves from a denser to a rarer medium.
Real-Life Example: Swimming pools often appear shallower than they actually are because of refraction.
Correct Answer: B. Refraction
13. The twinkling of stars occurs due to:
As starlight passes through different layers of the Earth’s atmosphere, it continuously bends because of changes in air density. This atmospheric refraction causes the apparent brightness and position of stars to change rapidly, making them appear to twinkle.
Key Points:
- Twinkling is caused by atmospheric refraction.
- Air density varies with temperature and altitude.
- Stars appear to change brightness because of continuous refraction.
Real-Life Example: Stars twinkle at night, whereas planets usually appear steady because they are closer and appear as extended sources of light.
Correct Answer: C. Atmospheric Refraction
14. The Sun appears a few minutes before sunrise due to:
Atmospheric refraction bends the Sun’s rays towards the Earth as they pass through the atmosphere. This makes the Sun appear slightly above its actual position, allowing us to see it a few minutes before the actual sunrise and after the actual sunset.
Key Points:
- Atmospheric refraction shifts the apparent position of the Sun.
- The apparent sunrise occurs before the actual sunrise.
- The apparent sunset occurs after the actual sunset.
Real-Life Example: Even when the Sun is below the horizon, it can still be seen because its light is refracted by the Earth’s atmosphere.
Correct Answer: C. Atmospheric Refraction
15. Which colour of light bends the least while passing through a prism?
When white light passes through a prism, different colours bend by different amounts because each colour has a different wavelength. Red light has the longest wavelength and undergoes the least deviation, while violet light bends the most.
Key Points:
- Red light has the longest wavelength.
- It experiences the least deviation in a prism.
- Different colours refract by different amounts, causing dispersion.
Real-Life Example: In a rainbow, red appears on the outer edge because it bends less than the other colours.
Correct Answer: D. Red
16. Which colour of light bends the most while passing through a prism?
When white light passes through a prism, each colour bends by a different amount because they have different wavelengths. Violet light has the shortest wavelength and the highest refractive index in glass, so it undergoes the greatest deviation.
Key Points:
- Violet light has the shortest wavelength.
- It experiences the maximum deviation in a prism.
- Different colours bend differently, producing the spectrum of visible light.
Real-Life Example: The violet colour in a rainbow appears on the inner side because it bends more than the other colours.
Correct Answer: D. Violet
17. Which optical device mainly uses a convex lens?
A magnifying glass uses a convex lens to produce a larger, upright virtual image of a nearby object. This helps us observe fine details that are difficult to see with the naked eye.
Key Points:
- A magnifying glass contains a convex lens.
- It enlarges the apparent size of nearby objects.
- The object must be placed within the focal length of the lens.
Real-Life Example: Scientists, jewellers, and stamp collectors use magnifying glasses to examine small objects in detail.
Correct Answer: A. Magnifying Glass
18. A concave lens causes parallel rays of light to:
A concave lens is a diverging lens that spreads parallel rays of light outward after refraction. The rays appear to originate from the principal focus on the same side of the lens, forming a virtual image.
Key Points:
- A concave lens diverges parallel light rays.
- The rays appear to come from the principal focus.
- It always forms virtual and diminished images.
Real-Life Example: Concave lenses in spectacles spread incoming light rays to help people with myopia see distant objects clearly.
Correct Answer: C. Diverge after Refraction
19. The ability of a lens to bend light depends mainly on its:
The amount by which a lens bends light depends on its shape and the refractive index of the material from which it is made. Lenses with different curvatures and materials have different optical powers and focal lengths.
Key Points:
- Lens shape affects how strongly light is refracted.
- The refractive index of the material also influences bending.
- Both factors determine the lens’s optical power.
Real-Life Example: Camera lenses are designed with different shapes and materials to produce sharp, high-quality images.
Correct Answer: B. Shape and Material
20. Which phenomenon is responsible for the formation of images by lenses?
Lenses form images by refracting light. As light passes through a lens, it changes direction, causing the rays to converge or diverge and produce either a real or virtual image depending on the type of lens and the object’s position.
Key Points:
- Image formation by lenses is based on refraction.
- Convex lenses can form real or virtual images.
- Concave lenses always form virtual images.
- Reflection is used by mirrors, while refraction is used by lenses.
Real-Life Example: Cameras, microscopes, telescopes, and the human eye all form images using the refraction of light through lenses.
Correct Answer: B. Refraction
Final Revision:
- Light bends towards the normal when it enters a denser medium because its speed decreases.
- Refractive Index = Speed of light in vacuum ÷ Speed of light in the medium.
- Convex lens is thicker at the centre, converges light, and is used as a magnifying glass.
- Concave lens is thinner at the centre, diverges light, and always forms a virtual, erect, and diminished image.
- Parallel rays passing through a convex lens meet at the principal focus, while a ray through the optical centre passes without deviation.
- A pencil appears bent in water and the apparent depth of water is less than the real depth due to refraction.
- Atmospheric refraction causes the twinkling of stars and the apparent early sunrise and delayed sunset.
- In a prism, Red light deviates the least, while Violet light deviates the most because of their different wavelengths.
- The shape and refractive index (material) of a lens determine how strongly it bends light.
- Lenses form images by refraction, whereas mirrors form images by reflection.
Further Reading :
To deepen your knowledge of TNPSC Physics Light, explore NCERT Class 10 Science – Light: Reflection and Refraction. This chapter clearly explains the core TNPSC Physics and General Science concepts, including reflection, refraction, spherical mirrors, lenses, image formation, and refractive index, making it an excellent resource for TNPSC and other competitive exam preparation.
