💡 Chapter 14: Light – Short Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
📖 What's Inside: This chapter covers reflection, refraction, total internal reflection, optical fibres, lenses, prisms, dispersion, and optical instruments. Each short question is presented with the exact exam-ready answer as per the official PECTAA 2026 Physics curriculum. Perfect for Punjab Boards (Lahore, Gujranwala, Multan, etc.) and all BISE boards across Pakistan.
📚 Related Resources – Chapter 14: Light
Light covers reflection, refraction, total internal reflection, optical fibres, lenses, prisms, dispersion, and optical instruments. Includes solved examples and numerical problems.
📑 Quick Jump to Questions
📖 Short Questions & Answers (PECTAA 2026)
1. Define light.
Light is a form of energy that travels in the form of waves and allows us to see the world around us.
Light is a form of energy that travels in the form of waves and allows us to see the world around us.
2. What is reflection of light?
Reflection of light takes place when light hits a surface and bounces back instead of passing through it. This usually occurs on smooth and shiny surfaces, such as mirrors.
OR
When light travelling in a certain medium fall on the surface of another medium, a part of it turns back in the same medium. This is called reflection of light.
Reflection of light takes place when light hits a surface and bounces back instead of passing through it. This usually occurs on smooth and shiny surfaces, such as mirrors.
OR
When light travelling in a certain medium fall on the surface of another medium, a part of it turns back in the same medium. This is called reflection of light.
3. Define terms normal, angle of incidence, and angle of reflection.
Normal: A line drawn perpendicular (90°) to the reflecting surface at the point where the incident ray strikes it.
Angle of Incidence (i): The angle between the incident ray and the normal at the point of incidence.
Angle of Reflection (r): The angle between the reflected ray and the normal at the point of reflection.
Normal: A line drawn perpendicular (90°) to the reflecting surface at the point where the incident ray strikes it.
Angle of Incidence (i): The angle between the incident ray and the normal at the point of incidence.
Angle of Reflection (r): The angle between the reflected ray and the normal at the point of reflection.
4. What are the types of reflection?
There are two types of reflection:
Regular/Specular Reflection: It takes place on smooth surfaces (like mirrors) where light reflects in one direction, forming a clear image.
Diffused/Irregular Reflection: It occurs on rough surfaces (like paper), where light scatters in different directions, so no clear image is seen.
There are two types of reflection:
Regular/Specular Reflection: It takes place on smooth surfaces (like mirrors) where light reflects in one direction, forming a clear image.
Diffused/Irregular Reflection: It occurs on rough surfaces (like paper), where light scatters in different directions, so no clear image is seen.
5. What are the laws of reflection?
The reflection of light follows two basic laws:
First Law: The incident ray, the reflected ray, and the normal all lie in the same plane.
Second Law: The angle of incidence (i) is always equal to the angle of reflection (r). i.e. ∠i = ∠r.
The reflection of light follows two basic laws:
First Law: The incident ray, the reflected ray, and the normal all lie in the same plane.
Second Law: The angle of incidence (i) is always equal to the angle of reflection (r). i.e. ∠i = ∠r.
6. What is refraction of light?
Refraction of light occurs when light changes direction as it passes from one medium to another, such as from air to water or glass. This happens because light travels at different speeds in different materials.
Refraction of light occurs when light changes direction as it passes from one medium to another, such as from air to water or glass. This happens because light travels at different speeds in different materials.
7. What happens when light moves between different media, and what does the amount of bending depend on?
When light moves from a rarer medium (air) to a denser medium (glass or water), it bends towards the normal.
When it moves from a denser medium to a rarer medium, it bends away from the normal.
The amount of bending depends on the refractive index of the medium.
When light moves from a rarer medium (air) to a denser medium (glass or water), it bends towards the normal.
When it moves from a denser medium to a rarer medium, it bends away from the normal.
The amount of bending depends on the refractive index of the medium.
8. What are the laws of refraction of light?
First Law: The incident ray, refracted ray, and the normal at the point where light enters a new medium all lie in the same plane.
Second Law (Snell's Law): The ratio of the sine of the angle of incidence i to the sine of the angle of refraction r remains constant for a specific pair of media.
\[ \frac{\sin i}{\sin r} = n \]
Here, n is the refractive index of the second medium relative to the first.
First Law: The incident ray, refracted ray, and the normal at the point where light enters a new medium all lie in the same plane.
Second Law (Snell's Law): The ratio of the sine of the angle of incidence i to the sine of the angle of refraction r remains constant for a specific pair of media.
\[ \frac{\sin i}{\sin r} = n \]
Here, n is the refractive index of the second medium relative to the first.
9. What is the refractive index?
It is defined as the ratio of the speed of light in air or vacuum c to the speed of light in the given medium v.
\[ n = \frac{c}{v} \]
Note: Speed of light in air is approximately 3.0 × 108 ms−1. However, when light travels through a medium, such as water or glass, its speed decreases. The speed of light in water is approximately 2.3 × 108 ms−1, while in glass, it is approximately 2.0 × 108 ms−1.
It is defined as the ratio of the speed of light in air or vacuum c to the speed of light in the given medium v.
\[ n = \frac{c}{v} \]
Note: Speed of light in air is approximately 3.0 × 108 ms−1. However, when light travels through a medium, such as water or glass, its speed decreases. The speed of light in water is approximately 2.3 × 108 ms−1, while in glass, it is approximately 2.0 × 108 ms−1.
10. Write any two characteristics of focus of a concave and a convex mirror.
| Concave Mirror | Convex Mirror |
|---|---|
| The focus is in front of the mirror | The focus lies behind the mirror |
| The focus is real as the rays of light after reflection converge at the focus. | The focus is virtual as the rays of light after reflection appear to come from the focus. |
11. Define prism.
A prism is a transparent optical object with at least two polished plane surfaces inclined towards each other.
It is usually made of optical glass and is used to refract (bend) light.
A prism is a transparent optical object with at least two polished plane surfaces inclined towards each other.
It is usually made of optical glass and is used to refract (bend) light.
12. What is critical angle?
The angle of incidence for which the angle of refraction is 90° is called the critical angle.
The angle of incidence for which the angle of refraction is 90° is called the critical angle.
13. What is total internal reflection?
Total internal reflection is the phenomenon of reflection of light ray back to the same medium when passing from denser medium to rarer medium in such a way that angle of incidence is greater than its critical angle.
Total internal reflection is the phenomenon of reflection of light ray back to the same medium when passing from denser medium to rarer medium in such a way that angle of incidence is greater than its critical angle.
14. Why do diamonds sparkle?
Diamonds sparkle because they have a very high refractive index, which causes multiple total internal reflections inside the diamond.
Diamonds sparkle because they have a very high refractive index, which causes multiple total internal reflections inside the diamond.
15. What principle do optical fibres use? Also write its uses.
Optical fibres use the principle of Total Internal Reflection (TIR) to transmit light efficiently over long distances.
Uses: These fibres are widely used in the telecommunication industry due to their high speed and reliability.
Optical fibres use the principle of Total Internal Reflection (TIR) to transmit light efficiently over long distances.
Uses: These fibres are widely used in the telecommunication industry due to their high speed and reliability.
16. What are optical fibres made of and what are their main parts?
An optical fibre consists of thin, hair-like strands made of glass or plastic.
Main parts: It has two main parts.
i. Core: The inner part that carries the light, made of a material with a higher refractive index.
ii. Cladding: The outer part surrounding the core, which has a lower refractive index and helps in total internal reflection.
An optical fibre consists of thin, hair-like strands made of glass or plastic.
Main parts: It has two main parts.
i. Core: The inner part that carries the light, made of a material with a higher refractive index.
ii. Cladding: The outer part surrounding the core, which has a lower refractive index and helps in total internal reflection.
17. How does light travel through an optical fibre?
When light enters one end of the core, it hits the core-cladding boundary at an angle greater than the critical angle, causing it to reflect back into the core. This repeated reflection allows light to travel long distances with minimal energy loss.
When light enters one end of the core, it hits the core-cladding boundary at an angle greater than the critical angle, causing it to reflect back into the core. This repeated reflection allows light to travel long distances with minimal energy loss.
18. What are the advantages of optical fibres?
Compared to traditional copper cables, optical fibres offer several key benefits:
i. High Bandwidth: Optical fibres can carry a much larger amount of data than copper wires. Bandwidth means how much data can be sent over a network per second. In today's world, where we need fast internet, optical fibres are the best choice because they support high-speed data transfer.
ii. Low Power Consumption: They use less power than copper cables. Also, because they last longer and are more durable, they reduce the cost of repairs and maintenance.
iii. Faster Speed: They send data using light pulses, which travel extremely fast almost at the speed of light.
iv. Long Distance Transmission: Optical fibres can carry data across very long distances without losing signal quality.
v. Resistance to Electrical Interference: Since optical fibres use light instead of electricity, they are not affected by electrical noise or interference.
Compared to traditional copper cables, optical fibres offer several key benefits:
i. High Bandwidth: Optical fibres can carry a much larger amount of data than copper wires. Bandwidth means how much data can be sent over a network per second. In today's world, where we need fast internet, optical fibres are the best choice because they support high-speed data transfer.
ii. Low Power Consumption: They use less power than copper cables. Also, because they last longer and are more durable, they reduce the cost of repairs and maintenance.
iii. Faster Speed: They send data using light pulses, which travel extremely fast almost at the speed of light.
iv. Long Distance Transmission: Optical fibres can carry data across very long distances without losing signal quality.
v. Resistance to Electrical Interference: Since optical fibres use light instead of electricity, they are not affected by electrical noise or interference.
19. Why can optical fibres send data around bends and corners without much loss?
Optical fibres use total internal reflection, which keeps light reflected inside the fibre and prevents significant signal loss.
Optical fibres use total internal reflection, which keeps light reflected inside the fibre and prevents significant signal loss.
20. Define lens also give uses.
Lens: A lens is a transparent material with two surfaces, at least one of which is curved.
It bends (refracts) light in a way that forms an image of an object.
Uses: Lenses come in different types and are widely used in optical devices such as cameras, eyeglasses, microscopes, telescopes, and projectors. They play an important role in correcting vision.
Lens: A lens is a transparent material with two surfaces, at least one of which is curved.
It bends (refracts) light in a way that forms an image of an object.
Uses: Lenses come in different types and are widely used in optical devices such as cameras, eyeglasses, microscopes, telescopes, and projectors. They play an important role in correcting vision.
21. What are the types of lens?
Lenses are classified into two categories:
(i) Convex (Converging) Lens
(ii) Concave (Diverging) Lens
Convex (Converging) Lens: A convex lens, also known as a converging lens, brings parallel light rays together at a point.
Shape: It is thicker in the centre and thinner at the edges.
Concave (Diverging) Lens: A concave lens, also called a diverging lens, causes parallel light rays to spread out.
Shape: This lens is thinner in the centre and thicker at the edges.
Lenses are classified into two categories:
(i) Convex (Converging) Lens
(ii) Concave (Diverging) Lens
Convex (Converging) Lens: A convex lens, also known as a converging lens, brings parallel light rays together at a point.
Shape: It is thicker in the centre and thinner at the edges.
Concave (Diverging) Lens: A concave lens, also called a diverging lens, causes parallel light rays to spread out.
Shape: This lens is thinner in the centre and thicker at the edges.
22. What is focal length?
The focal length (f) is the distance from the lens (optical centre) to the principal focus, where light rays either meet (converge) or appear to spread out (diverge).
The focal length (f) is the distance from the lens (optical centre) to the principal focus, where light rays either meet (converge) or appear to spread out (diverge).
23. What is the focal length of converging and diverging lenses?
In converging lenses, focal length is positive and the rays meet at a point after passing through the lens.
In diverging lenses, focal length is negative and rays seem to spread out from a virtual point on the same side of the lens as the light source.
In converging lenses, focal length is positive and the rays meet at a point after passing through the lens.
In diverging lenses, focal length is negative and rays seem to spread out from a virtual point on the same side of the lens as the light source.
24. What is the principal axis?
This is a straight, imaginary line that passes through the centre of the lens. Light rays that travel along the principal axis do not bend or change direction when passing through the lens.
This is a straight, imaginary line that passes through the centre of the lens. Light rays that travel along the principal axis do not bend or change direction when passing through the lens.
25. What is principal focus (focal point)?
The principal focus is the point on principal axis where light rays that are parallel to the principal axis come together (in converging lenses) or appear to come from (in diverging lenses).
The principal focus is the point on principal axis where light rays that are parallel to the principal axis come together (in converging lenses) or appear to come from (in diverging lenses).
26. Where is the principal focus formed in converging and diverging lenses?
For a converging lens, the focus is on the opposite side of the incoming rays.
For a diverging lens, the focus is on the same side as the incoming rays and appears to be behind the lens.
For a converging lens, the focus is on the opposite side of the incoming rays.
For a diverging lens, the focus is on the same side as the incoming rays and appears to be behind the lens.
27. What is the optical centre?
The optical centre is the geometrical middle point of the lens through which the principal axis passes.
Light passing through this point does not bend. It is usually marked as O.
The optical centre is the geometrical middle point of the lens through which the principal axis passes.
Light passing through this point does not bend. It is usually marked as O.
28. What is the centre of curvature?
Lenses are made from parts of a sphere. The centre of this imaginary sphere is called the center of curvature.
It is generally located at twice the focal length from the lens.
Lenses are made from parts of a sphere. The centre of this imaginary sphere is called the center of curvature.
It is generally located at twice the focal length from the lens.
29. What is the lens/mirror formula?
The relationship between the focal length f, object distance p, and image distance q for both lenses and mirrors is expressed by the lens/mirror formula as:
\[ \frac{1}{f} = \frac{1}{p} + \frac{1}{q} \]
The relationship between the focal length f, object distance p, and image distance q for both lenses and mirrors is expressed by the lens/mirror formula as:
\[ \frac{1}{f} = \frac{1}{p} + \frac{1}{q} \]
30. What is the focal point of a converging lens?
When a set of parallel light rays pass through a converging lens, they refract and bend towards the principal axis. After passing through the lens, all the rays meet at a common point on the principal axis; this is known as the focal point.
When a set of parallel light rays pass through a converging lens, they refract and bend towards the principal axis. After passing through the lens, all the rays meet at a common point on the principal axis; this is known as the focal point.
31. What is a focal point in a diverging lens?
In a diverging lens, parallel rays do not actually meet after refraction. Instead, when extended backward, they appear to spread out from a common point on the same side of the lens. This point is called the virtual focal point.
In a diverging lens, parallel rays do not actually meet after refraction. Instead, when extended backward, they appear to spread out from a common point on the same side of the lens. This point is called the virtual focal point.
32. Describe briefly how a convex lens forms a real or virtual image.
A convex lens generally forms a real and inverted image when the object is placed beyond the focal point. The image is formed on the opposite side of the lens.
If the object is placed within the focal length, the lens forms a virtual and upright image.
A convex lens generally forms a real and inverted image when the object is placed beyond the focal point. The image is formed on the opposite side of the lens.
If the object is placed within the focal length, the lens forms a virtual and upright image.
33. What type of image is formed by a diverging lens?
When an object is placed far from a diverging lens (at infinity), the image formed is virtual, upright, and smaller than the actual object.
When an object is placed far from a diverging lens (at infinity), the image formed is virtual, upright, and smaller than the actual object.
34. Define power of lens also write its formula and SI unit.
The reciprocal of focal length (f) is called power of a lens. It is given by the formula:
\[ P = \frac{1}{f} \]
SI Unit: The SI unit of power of a lens is "Dioptre", denoted by a symbol D. If f is expressed in metres so that
\[ 1D = 1m^{-1} \]
Thus, 1 Dioptre is the power of a lens whose focal length is 1 metre.
The reciprocal of focal length (f) is called power of a lens. It is given by the formula:
\[ P = \frac{1}{f} \]
SI Unit: The SI unit of power of a lens is "Dioptre", denoted by a symbol D. If f is expressed in metres so that
\[ 1D = 1m^{-1} \]
Thus, 1 Dioptre is the power of a lens whose focal length is 1 metre.
35. What is the sign of power for convex and concave lenses?
A convex lens has a positive focal length, so its power is positive.
A concave lens has a negative focal length, so its power is negative.
A convex lens has a positive focal length, so its power is positive.
A concave lens has a negative focal length, so its power is negative.
36. What are the rules for image formation by a convex lens?
For a convex lens, image formation follows three rules:
i. A ray parallel to the principal axis passes through the focal point F after refraction from the lens (ray-1).
ii. A ray passing through the optical centre of the lens continues straight without bending (ray-2).
iii. A ray passing through the focal point after refraction from the lens, becomes parallel to the principal axis (ray-3).
For a convex lens, image formation follows three rules:
i. A ray parallel to the principal axis passes through the focal point F after refraction from the lens (ray-1).
ii. A ray passing through the optical centre of the lens continues straight without bending (ray-2).
iii. A ray passing through the focal point after refraction from the lens, becomes parallel to the principal axis (ray-3).
37. What type of image is formed when an object is placed at infinity in front of a convex lens?
The image is formed at F highly diminished (point-sized), and is real and inverted.
The image is formed at F highly diminished (point-sized), and is real and inverted.
38. What type of image is formed when an object is placed beyond 2F of a convex lens?
The image is between F and 2F, real, inverted, smaller (diminished) than the object.
The image is between F and 2F, real, inverted, smaller (diminished) than the object.
39. What type of image is formed when an object is placed at 2F of a convex lens?
The image is at 2F, real, inverted, the same size as the object.
The image is at 2F, real, inverted, the same size as the object.
40. What type of image is formed when an object is placed between F and 2F of a convex lens?
The image is beyond 2F, real, inverted, larger than the object.
The image is beyond 2F, real, inverted, larger than the object.
41. What type of image is formed when an object is placed at F of a convex lens?
The image is formed at infinity, highly enlarged, real, and inverted.
The image is formed at infinity, highly enlarged, real, and inverted.
42. What type of image is formed when an object is placed between a convex lens and F?
The image is behind the object, virtual, erect, larger than the object.
The image is behind the object, virtual, erect, larger than the object.
43. When does a convex lens produce a real image?
A convex lens produces a real image when the object is placed beyond 2F. The image appears on the opposite side of the lens from where the object is located.
A convex lens produces a real image when the object is placed beyond 2F. The image appears on the opposite side of the lens from where the object is located.
44. When does a convex lens produce a virtual image?
For a convex lens to produce a magnified virtual image, the object should be placed within the focal length of the lens. In this arrangement, the image appears on the same side of the lens as the object. It is upright, larger in size, and cannot be projected onto a screen, as it is virtual.
For a convex lens to produce a magnified virtual image, the object should be placed within the focal length of the lens. In this arrangement, the image appears on the same side of the lens as the object. It is upright, larger in size, and cannot be projected onto a screen, as it is virtual.
45. Why is the image in a plane mirror considered virtual, even though it looks real?
The image in a plane mirror is considered virtual because the light rays do not actually meet behind the mirror. They only appear to come from behind the mirror, so the image cannot be formed on a screen.
The image in a plane mirror is considered virtual because the light rays do not actually meet behind the mirror. They only appear to come from behind the mirror, so the image cannot be formed on a screen.
46. What is the difference between real and virtual images?
| Real Image | Virtual Image |
|---|---|
| Can be displayed or captured on a screen. | Cannot be projected or caught on a screen. |
| Always appears upside down (inverted). | Always appears upright (erect). |
| Created when light rays actually meet after reflecting or refracting. | Created when light rays only seem to meet, they do not actually converge. |
| Result of actual light rays intersecting. | Formed by the imaginary extension of diverging light rays. |
47. What is linear magnification?
Linear magnification is the ratio of the height (or length) of the image to the height (or length) of the object.
It indicates how much larger or smaller the image is compared to the object.
\[ M = \frac{h_i}{h_o} \]
Linear magnification is the ratio of the height (or length) of the image to the height (or length) of the object.
It indicates how much larger or smaller the image is compared to the object.
\[ M = \frac{h_i}{h_o} \]
48. What is a magnifying glass?
A magnifying glass is a convex (converging) lens used to make objects appear larger.
When an object is placed closer to the lens than its focal length, it forms a virtual, upright, and magnified image. This simple use of a convex lens is also known as a simple microscope.
A magnifying glass is a convex (converging) lens used to make objects appear larger.
When an object is placed closer to the lens than its focal length, it forms a virtual, upright, and magnified image. This simple use of a convex lens is also known as a simple microscope.
49. How does a camera work?
A camera consists of a light-proof box with a convex lens at the front and a light-sensitive film or sensor at the back.
The lens focuses light onto the film to capture an image. The image formed on the film is real, inverted, and smaller (diminished).
A camera consists of a light-proof box with a convex lens at the front and a light-sensitive film or sensor at the back.
The lens focuses light onto the film to capture an image. The image formed on the film is real, inverted, and smaller (diminished).
50. How does a slide projector work?
A slide projector works by projecting an enlarged image of a slide or film onto a screen. It consists of:
i. A light source at the centre of a concave mirror, which reflects light as parallel rays.
ii. A condenser lens system (two plane convex lenses) that evenly distributes light across the slide.
iii. A projection lens (convex lens) that creates a real, large, and inverted image on the screen.
The slide is placed upside down and positioned between F and 2F to form a real, magnified, and inverted image on the screen.
A slide projector works by projecting an enlarged image of a slide or film onto a screen. It consists of:
i. A light source at the centre of a concave mirror, which reflects light as parallel rays.
ii. A condenser lens system (two plane convex lenses) that evenly distributes light across the slide.
iii. A projection lens (convex lens) that creates a real, large, and inverted image on the screen.
The slide is placed upside down and positioned between F and 2F to form a real, magnified, and inverted image on the screen.
51. How does a photograph enlarger work?
A photograph enlarger works similarly to a slide projector and is used to enlarge photographic negatives onto photographic paper.
The negative is placed between F and 2F, forming a real, inverted, and enlarged image on the paper.
The convex lens ensures that the final image is magnified, allowing small negatives to be printed as large photographs.
A photograph enlarger works similarly to a slide projector and is used to enlarge photographic negatives onto photographic paper.
The negative is placed between F and 2F, forming a real, inverted, and enlarged image on the paper.
The convex lens ensures that the final image is magnified, allowing small negatives to be printed as large photographs.
52. How is an image formed in a normal eye?
In a healthy eye, light rays from an object pass through the cornea and lens, and are focused directly onto the retina, forming a sharp and clear image.
Rays from the top and bottom of the object converge at specific points on the retina, allowing us to see a clear image.
This process is similar to how a convex lens forms a real image.
In a healthy eye, light rays from an object pass through the cornea and lens, and are focused directly onto the retina, forming a sharp and clear image.
Rays from the top and bottom of the object converge at specific points on the retina, allowing us to see a clear image.
This process is similar to how a convex lens forms a real image.
53. Define near point.
The closest distance from the eye where we can see things clearly is called near point.
For a normal person, it is about 25 cm.
The closest distance from the eye where we can see things clearly is called near point.
For a normal person, it is about 25 cm.
54. What is short-sightedness (myopia)?
Short-sightedness is a condition where a person can clearly see nearby objects but struggles to see distant ones.
Short-sightedness is a condition where a person can clearly see nearby objects but struggles to see distant ones.
55. Why do distant objects look blurry in short-sightedness and what are its causes?
Short-sightedness occurs when the eye lens bends light rays too strongly, causing the image to form in front of the retina instead of on it. As a result, distant objects look blurry.
There are two main causes of short-sightedness:
i. Lens too strong: The eye lens becomes too curved, focusing light in front of the retina.
ii. Eyeball too large: The distance between the cornea and retina increases, so the focused image falls short of the retina.
Short-sightedness occurs when the eye lens bends light rays too strongly, causing the image to form in front of the retina instead of on it. As a result, distant objects look blurry.
There are two main causes of short-sightedness:
i. Lens too strong: The eye lens becomes too curved, focusing light in front of the retina.
ii. Eyeball too large: The distance between the cornea and retina increases, so the focused image falls short of the retina.
56. How is short-sightedness corrected?
To correct short-sightedness, concave lenses are used in glasses or contact lenses. A concave lens spreads out the light rays before they enter the eye, helping the eye's natural lens to focus them correctly on the retina.
To correct short-sightedness, concave lenses are used in glasses or contact lenses. A concave lens spreads out the light rays before they enter the eye, helping the eye's natural lens to focus them correctly on the retina.
57. What is long-sightedness (hypermetropia)?
In long-sightedness, a person can see distant objects clearly, but nearby objects appear blurry.
In long-sightedness, a person can see distant objects clearly, but nearby objects appear blurry.
58. Why do nearby objects appear blurry in long-sightedness and what are its causes?
This happens when the eye lens is too weak or the eyeball is too small, so the light rays from near objects are not bent enough. As a result, the rays focus behind the retina instead of on it.
There are two main causes:
i. Lens too weak: The lens does not bend the light rays enough.
ii. Eyeball too small: The retina is too close to the lens.
In both cases, the image is formed behind the retina, making close-up vision blurry.
This happens when the eye lens is too weak or the eyeball is too small, so the light rays from near objects are not bent enough. As a result, the rays focus behind the retina instead of on it.
There are two main causes:
i. Lens too weak: The lens does not bend the light rays enough.
ii. Eyeball too small: The retina is too close to the lens.
In both cases, the image is formed behind the retina, making close-up vision blurry.
59. How is long-sightedness corrected?
To correct long-sightedness, convex lenses are used in glasses or contact lenses. A convex lens bends the light rays more before they enter the eye, helping them focus directly on the retina.
To correct long-sightedness, convex lenses are used in glasses or contact lenses. A convex lens bends the light rays more before they enter the eye, helping them focus directly on the retina.
60. What is gravitational lensing?
Gravitational lensing occurs when the strong gravitational field of a massive object, like a black hole or galaxy, bends the path of light travelling near it. Just like an optical lens bends and focuses light, a massive celestial body acts as a "gravitational lens", altering the path of light from a distant object such as a star or galaxy.
Gravitational lensing occurs when the strong gravitational field of a massive object, like a black hole or galaxy, bends the path of light travelling near it. Just like an optical lens bends and focuses light, a massive celestial body acts as a "gravitational lens", altering the path of light from a distant object such as a star or galaxy.
61. How does gravitational lensing help scientists?
Gravitational lensing is a valuable tool in astronomy. It helps scientists study distant galaxies, dark matter, and the structure of the universe, providing insights into objects that are otherwise too far to observe directly.
Gravitational lensing is a valuable tool in astronomy. It helps scientists study distant galaxies, dark matter, and the structure of the universe, providing insights into objects that are otherwise too far to observe directly.
62. What are acoustic lenses?
Acoustic lenses are special devices designed to focus or spread sound waves, similar to how optical lenses control light.
They are made from materials with different acoustic properties and are shaped to redirect and focus sound waves. They can concentrate sound into a narrow beam or spread it over a wider area.
Acoustic lenses are special devices designed to focus or spread sound waves, similar to how optical lenses control light.
They are made from materials with different acoustic properties and are shaped to redirect and focus sound waves. They can concentrate sound into a narrow beam or spread it over a wider area.
63. What are the uses of acoustic lenses?
Acoustic lenses are widely used in:
i. Medical imaging (e.g., ultrasound) to improve scanning accuracy.
ii. SONAR systems to detect underwater objects.
iii. Noise control to focus or reduce sound in specific areas.
Acoustic lenses are widely used in:
i. Medical imaging (e.g., ultrasound) to improve scanning accuracy.
ii. SONAR systems to detect underwater objects.
iii. Noise control to focus or reduce sound in specific areas.
64. What is dispersion of light?
The splitting of white light into its seven constituent colours when passing through a prism is called dispersion of light.
The splitting of white light into its seven constituent colours when passing through a prism is called dispersion of light.
65. How does dispersion of light occur in a prism?
When white light enters a prism, each wavelength refracts at a different angle. As a result, the light separates into seven distinct colours: red, orange, yellow, green, blue, indigo, and violet, forming the visible light spectrum.
When white light enters a prism, each wavelength refracts at a different angle. As a result, the light separates into seven distinct colours: red, orange, yellow, green, blue, indigo, and violet, forming the visible light spectrum.
66. Which colours bend more and less in a prism?
Shorter wavelengths (violet, blue) bend more than longer wavelengths (red, orange).
Shorter wavelengths (violet, blue) bend more than longer wavelengths (red, orange).
67. Can prisms disperse light beyond the visible spectrum?
Yes, prisms can also disperse infrared (IR) and ultraviolet (UV) light, though these wavelengths are invisible to the human eye.
Yes, prisms can also disperse infrared (IR) and ultraviolet (UV) light, though these wavelengths are invisible to the human eye.
68. What are infrared thermometers? How do infrared thermometers work?
Infrared thermometers are devices that detect IR radiation emitted by objects to measure temperature.
Working: They analyse the intensity of IR radiation and determine the temperature of the emitting object.
Infrared thermometers are devices that detect IR radiation emitted by objects to measure temperature.
Working: They analyse the intensity of IR radiation and determine the temperature of the emitting object.
69. What is the main advantage of infrared thermometer technology?
This technology allows for non-contact temperature measurement, such as checking human body temperature.
This technology allows for non-contact temperature measurement, such as checking human body temperature.
📐 Key Formulas – Light
Refractive Index: \( n = \frac{c}{v} \)
Snell's Law: \( n_1 \sin i = n_2 \sin r \)
Critical Angle: \( C = \sin^{-1} \left( \frac{1}{n} \right) \)
Mirror / Lens Formula: \( \frac{1}{f} = \frac{1}{p} + \frac{1}{q} \)
Magnification: \( M = \frac{h_i}{h_o} = -\frac{q}{p} \)
Power of Lens: \( P = \frac{1}{f} \)
Unit 10Thermal Physics
Unit 11Transfer of Thermal Energy
Unit 12Waves
Unit 13Sound
Unit 14✨ Light
Unit 15Electrostatics
Unit 16Electricity
Unit 17Electromagnetism
Unit 18Electromagnetic Induction & EM Waves
Unit 19Electronics
Unit 20Atomic and Nuclear Physics
Unit 21Space and Environment
📖 Complete syllabus coverage for Class 10 Physics (PECTAA 2026) – Units 10 to 21
💡 Exam Tip:
For board exams, define key terms precisely, mention formulas with units, and relate to real-life examples. These questions follow the PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus