Light Class 8 Important Questions and Answers (for 2025-26 Exam)

Light and reflection form two of the most vital chapters for Class 8 Science Syllabus—especially when learning about the human eye and how light behaves. Whether you’re struggling with ray diagrams, surface reflections or the way the eye adapts to light and dark, consistent practice is the key. Without solving a variety of questions, even the best concepts won’t turn into exam-ready confidence.

This comprehensive guide leaves no stone unturned: you’ll find important questions on light for Class 8, carefully crafted MCQs, in-depth numerical problems, and diagram-based questions tailored for the human eye topic and reflection. If you want to aim for full marks, this resource covers every type of question you will encounter.

We include full-length NCERT solutions for Class 8 Science Chapter “Light”, plus bonus Light Class 8 extra questions—all focused on reflection and the human eye—to help you score full marks. With these Light Class 8 extra questions and detailed solutions, you’ll build the clarity and speed required to outperform your peers.

Important Questions Class 8 Science Chapter 16 – With Solutions

Our Class 8 Science Chapter 16 – Light Important Questions and Answers have been carefully compiled from multiple trusted sources to provide students with a comprehensive question bank in one place. Each question includes detailed, step-by-step answers prepared by our experienced Science faculty, ensuring conceptual clarity and exam readiness.

By practicing these Class 8 Light questions, students can thoroughly revise all key topics such as laws of reflection, human eye, and dispersion of light, helping them strengthen their understanding and score better in exams.

What are the important topics in Light (Class 8)?

The most important topics are:

1. What is Light & Laws of Reflection
2. Regular vs. Diffused Reflection
3. Structure and Working of the Human Eye (including Rods and Cones)
4. The Braille System
5. Dispersion of Light (Prisms)
6. Working of a Kaleidoscope

1. What is Light & Laws of Reflection

Light is a form of energy that allows us to see objects when light from them enters our eyes — either emitted by the object or reflected from it. 
The laws of reflection state:

• Law 1: The angle of incidence (∠i) equals the angle of reflection (∠r).
• Law 2: The incident ray, the reflected ray, and the normal to the reflecting surface all lie in the same plane. 
  In exam-style you can write:

When a ray of light hits a smooth surface, it is reflected such that ∠i = ∠r and all three (incident ray, reflected ray, normal) lie on one plane.
This topic is foundational for all subsequent optical phenomena.

2. Regular vs. Diffused Reflection

When parallel rays of light hit a smooth, polished surface, they reflect as parallel rays—this is regular reflection (or specular). When the surface is rough or irregular, the reflected rays scatter in many directions—this is diffused (or irregular) reflection. 

Important for exam answers: Regular reflection gives clear images (e.g., a mirror), diffused reflection does not form clear images (e.g., a rough wall). Also emphasise that even in diffused reflection the laws of reflection are still valid for each ray. 

3. Structure and Working of the Human Eye (including Rods and Cones)

The human eye is a complex optical instrument. Key parts: cornea, iris, pupil, lens, retina, and optic nerve.  Light enters through the cornea → pupil → lens focuses it on the retina. The retina has two types of photoreceptor cells: rods (sensitive in dim light) and cones (detect colour in bright light). 

In brief exam answer format: Light enters the eye, is focused by the lens onto the retina, where rods and cones convert light into electrical signals that travel to the brain via the optic nerve.
Understanding this topic is vital for vision-related questions and defects of vision.

4. The Braille System

The Braille system is a tactile writing system used by visually impaired (blind) persons, comprising raised dots arranged in cells representing letters and numbers. 

In exam-style:

Braille enables visually impaired students to read and write by feeling raised dot patterns; it is an important social application of the “Light” chapter since it addresses how blind persons perceive and access information even when light-based vision is impaired.
Including this topic shows awareness of inclusive education and real-life application.

5. Dispersion of Light (Prisms)

Dispersion is the splitting of white light into its constituent colours (VIBGYOR) when it passes through a transparent medium like a prism. 

Exam answer key points:

White light consists of various colours; when it passes through a prism, each colour bends differently due to different refractive indices, resulting in a spectrum. This phenomenon is called dispersion.
Include an example: rainbow, or white light through a triangular glass prism. This topic connects to practical phenomena and optical experiments.

6. Working of a Kaleidoscope

A kaleidoscope is an optical instrument that produces beautiful symmetric patterns by multiple reflections of light between mirrors.

 Exam-style explanation:

When light enters a kaleidoscope, it reflects off two or more inclined plane mirrors placed inside the tube. Multiple reflections cause repeated symmetrical images of coloured glass pieces inside, creating a changing design as the instrument is rotated.

Mention also that the underlying principle is multiple reflections (built on laws of reflection) and symmetry. Knowing this device’s working demonstrates understanding of applied optics.

Light Class 8 MCQs (Multiple Choice Questions) with Answers

Mark the correct option and give a brief, exam-style explanation of Class 8 Light MCQs (concept first, then reason).

The law “∠i = ∠r” refers to:

A) Refraction

B) Reflection

C) Dispersion

D) Diffraction

Ans: B. In reflection, the angle of incidence equals the angle of reflection; rays and normal lie in one plane.

Image in a plane mirror is:

A) Real, inverted

B) Diminished

C) Virtual, laterally inverted, same size

D) Magnified

Ans: C. Plane mirrors produce virtual, upright, laterally inverted images of equal size.

Regular reflection occurs from:

A) Rough wall

B) Paper

C) Polished mirror

D) Chalk powder

Ans: C. Smooth surfaces reflect parallel rays in parallel, giving clear images.

Diffused reflection happens because:

A) Laws of reflection fail

B) Surface irregularities scatter rays

C) Light speed changes

D) Absorption only

Ans: B. Both types still obey the laws; roughness causes scattering.

The part of eye that controls light entry (aperture) is:

A) Retina

B) Pupil

C) Lens

D) Optic nerve

Ans: B. Iris regulates pupil size to adjust incoming light; image forms on retina.

Cells sensitive to dim light are:

A) Rods

B) Cones

C) Bipolar cells

D) Ganglion cells

Ans: A. Rods work in low light; cones for bright light and colour vision.

Braille is used by:

A) Colour-blind persons

B) Visually chged persons

C) Hearing impaired

D) Dyslexic learners

Ans: B. Braille is a tactile script read by touch (raised dots).

Kaleidoscope works on:

A) Refraction

B) Multiple reflections

C) Diffraction

D) Interference

Ans: B. Mirrors at angles produce repeated symmetric patterns.

White light splits into colours in a prism because of:

A) Reflection

B) Scattering

C) Dispersion (wavelength-dependent refraction)

D) Polarisation

Ans: C. Each colour bends differently; order is V-I-B-G-Y-O-R.

The colour band from violet to red is called:

A) Spectrum (VIBGYOR)

B) Monochrome

C) Filter

D) Shadow

Ans: A. Prism dispersion produces a continuous spectrum.

Which is true for diffused reflection?

A) ∠i ≠ ∠r

B) Rays reflect in many directions due to roughness

C) No image can ever form

D) Laws fail

Ans: B. Scatter occurs but laws still hold at each point.

Blind spot means:

A) Retina richest in cones

B) No photoreceptors; optic nerve leaves eye

C) Lens defect

D) Cataract region

Ans: B. No rods or cones present, hence no image detection.

Lateral inversion means:

A) Top–bottom swap

B) Left–right reversal in mirror image

C) Front–back swap

D) Rotation of object

Ans: B. Characteristic of plane mirror images.

In a dark room, reading is difficult mainly because:

A) Lens absent

B) Cones require bright light

C) Rods non-functional

D) Iris closed

Ans: B. Cones support colour/detail in bright light; rods handle dim vision.

Which statement about rainbow is correct?

A) Pure reflection only

B) Combination of refraction, dispersion, and internal reflection

C) Only diffraction

D) Polarisation only

Ans: B. Sunlight disperses and internally reflects in raindrops to form a spectrum arc.

Important Questions and Answers for Class 8 Science Light (Short & Very Short)

What is reflection of light Class 8?

Answer: Reflection of light is the phenomenon by which a ray of light falling on a surface bounces back into the same medium. For example, when a beam of light strikes a mirror, it is reflected off the mirror surface.  In simple terms: Light hits a surface + comes back = reflection.

What are the 2 laws of reflection?

Answer:

1. The angle of incidence (∠i) is equal to the angle of reflection (∠r).
2. The incident ray, the reflected ray and the normal to the reflecting surface all lie in the same plane. 

What is the difference between Regular and Diffused Reflection?

Answer:

What is dispersion of light?

Answer: Dispersion of light is the process by which white light splits into its component colours when passing through a transparent medium like a prism. For example, when sunlight passes through a triangular glass prism, it separates into red, orange, yellow, green, blue, indigo and violet (VIBGYOR). 
A natural example is a rainbow, where water droplets act like prisms and disperse sunlight. 

What is a ray of light?

Answer: A ray of light is an imaginary line that represents the path along which light energy travels. It starts at the source and goes in one direction. In diagrams, it is shown as a straight arrow pointing away from the source.

What is the normal in light reflection?

Answer: The normal is an imaginary line drawn perpendicular (90°) to the reflecting surface at the point of incidence (where the incident ray strikes). It helps measure the angles of incidence and reflection. 

Why does a mirror form a virtual image?

Answer: A plane mirror forms a virtual image because the reflected rays appear to diverge from a point behind the mirror; no real light rays converge at that point. The image is upright and of the same size as the object, but laterally inverted.

What happens to a beam of light in regular reflection?

Answer: In regular reflection, when a parallel beam of light rays falls on a smooth and polished surface, the rays are reflected in parallel. Because of this, a clear and sharp image is produced. 

What happens to a beam of light in diffused reflection?

Answer: In diffused reflection, when a parallel beam of light falls on a rough surface, the rays reflect in many directions, because the tiny irregularities cause scattering. Thus no clear image is formed. 

What is the spectrum of white light?

Answer: The spectrum of white light refers to its constituent colours (red, orange, yellow, green, blue, indigo, violet) as seen when white light is dispersed (for example, by a prism or water droplets). The order is typically red (least deviation) to violet (most deviation). 

What is a prism?

Answer: A prism is a transparent optical element, usually with triangular cross-section, that can refract and disperse white light into its component colours. It causes different wavelengths to bend by different amounts, thereby splitting the light. 

What is the cause of dispersion of light through a prism?

Answer: Dispersion occurs because different colours (wavelengths) of light travel at different speeds in a medium and thus refract by different amounts. For example, violet bends more than red when passing through a prism. 

What is a rainbow?

Answer: A rainbow is a natural optical phenomenon in which sunlight is refracted, internally reflected, and dispersed by many tiny water droplets in the atmosphere, forming a multi-coloured circular arc (order: red outside, violet inside). 

What is the human eye?

Answer: The human eye is a sense organ that detects light and produces images. It has parts such as the cornea, iris, pupil, lens, retina (with rods and cones) and optic nerve. It helps us see by focusing light and converting it into nerve signals sent to the brain. 

What are rods and cones?

Answer: Rods and cones are the two types of photoreceptor cells found in the retina of the human eye.

• Rods: sensitive to dim light, enable night vision but don’t detect colours.
• Cones: active in bright light, enable colour vision and sharp detail.

Q1: Explain the structure and working of the human eye with a neat, labeled diagram.

Answer:

The human eye is one of the most important sense organs. It works like a camera, allowing us to see the world around us by using light.

Structure of the Human Eye:

• Cornea: The transparent, dome-shaped outer layer at the front of the eye. It helps to refract, or bend, most of the light that enters.
• Iris: The colored part of the eye (like blue, brown, or green). Its job is to control the amount of light entering the eye.
• Pupil: The black opening in the center of the iris. The iris makes the pupil larger in dim light (to let more light in) and smaller in bright light (to let less light in).
• Lens: A convex lens (it bulges outwards) located just behind the pupil. It fine-tunes the focusing of light onto the retina.
• Retina: The light-sensitive layer at the back of the eye, similar to the film in a camera. It contains two types of special nerve cells: rods and cones.
• Optic Nerve: A bundle of nerves that connects the retina to the brain.

Working of the Human Eye:

1. Entry of Light: Light rays from an object first enter the eye through the cornea.
2. Focusing: The cornea and then the lens work together to focus the light. They form a real, inverted (upside-down) image on the retina.
3. Image Formation: When light hits the retina, the light-sensitive rods and cones get activated.
4. Signal to Brain: These cells generate electrical signals. The optic nerve carries these signals from the eye to the brain.
5. Perception: The brain processes these signals and interprets the image, allowing us to see the object upright and in its correct form.

Q2: What is the difference between Rods and Cones?

Answer:

Rods and cones are the two types of photoreceptor (light-sensitive) cells found in the retina of the human eye. They are both crucial for vision but have different functions.

In simple terms, rods help you see shapes in the dark, while cones help you see colors clearly in the daytime.

Q3: What is the Braille system? Explain how it is used.

Answer:

The Braille system is a tactile (related to touch) reading and writing system used by people who are visually impaired or blind. It was invented in 1824 by Louis Braille.

How the Braille System Works:

• The Braille Cell: The system is based on a cell made of six raised dots, arranged in two columns of three dots each (like the number six on a dice).
• Combinations: There are 64 possible combinations of these raised dots (including a blank cell).
• Reading: Each combination represents a letter, number, punctuation, or common word. People read Braille by moving their fingertips over the raised dots.
• Writing: Braille can be written using a slate and stylus (which punches dots on paper) or with a Braille typewriter like the Perkins Brailler.

The Braille system is a vital resource that allows visually impaired individuals to read, write, and access education independently.

Q4: Explain the construction and working of a Kaleidoscope.

Answer:

A kaleidoscope is an optical toy that creates beautiful, symmetrical patterns using the principle of multiple reflections.

Construction of a Kaleidoscope:

• Three Rectangular Mirrors: Equal-sized plane mirrors joined to form a prism with reflecting surfaces facing inward (usually at 60° angles).
• A Tube: The prism of mirrors is placed inside a cylindrical tube.
• Viewing Hole: One end has a small peephole for observation.
• Object Chamber: The other end contains two glass discs—one transparent, one ground glass—with colorful objects like beads or glass pieces in between.

Working of a Kaleidoscope:

1. Light enters through the ground glass, illuminating the colored objects.
2. The mirrors reflect the images of these objects repeatedly.
3. The image formed by one mirror acts as the object for others, producing multiple reflections.
4. Because the mirrors are at 60°, the reflections form a symmetrical hexagonal pattern.
5. Rotating the tube changes the arrangement, creating new patterns each time.

Q5: State and explain the two laws of reflection with a diagram.

Answer:

Reflection of light is the phenomenon of light bouncing back after striking a smooth surface, such as a plane mirror. This process follows two laws known as the Laws of Reflection.

Terms to Know:

• Incident Ray: The ray that strikes the surface.
• Reflected Ray: The ray that bounces back from the surface.
• Normal: An imaginary line drawn perpendicular (90°) to the surface at the point of incidence.
• Angle of Incidence (∠i): The angle between the incident ray and the normal.
• Angle of Reflection (∠r): The angle between the reflected ray and the normal.

The Two Laws of Reflection:

1. First Law: The angle of incidence is equal to the angle of reflection.
   That is: ∠i = ∠r
2. Second Law: The incident ray, reflected ray, and the normal at the point of incidence all lie in the same plane.

Example: If a ray of light strikes a mirror at 30° to the normal, it reflects back at 30° on the other side of the normal. All three lines can be drawn on the same plane (sheet of paper).

Important Solved Numericals for Class 8 Light

To score full marks, you must practice the light class 8 numericals. These problems mainly test your understanding of the laws of reflection and the properties of plane mirrors. Below are 8 important solved questions with detailed, step-by-step answers.

Question: An incident ray strikes a plane mirror such that the angle of incidence is 35°. What will be the angle of reflection?

Answer:

• Given:
  • The angle of incidence (i) = 35°
• To Find:
  • The angle of reflection (r)
• Concept (Formula):
  • This problem is based on the First Law of Reflection.
  • This law states that the angle of incidence is always equal to the angle of reflection.
  • The angle of incidence (i) is the angle between the incident ray and the normal (the 90° line to the mirror).
  • The angle of reflection (r) is the angle between the reflected ray and the normal.
  • Therefore, the formula is: Angle i = Angle r
• Solution:
  • We are given that the angle of incidence (i) = 35°.
  • According to the First Law of Reflection, r = i.
  • Therefore, r = 35°.

Final Answer: The angle of reflection will be 35°.

Question: A ray of light strikes a plane mirror at an angle of 25° with the mirror surface. What will be the angle of reflection?

Answer:

• Given:
  • The angle between the incident ray and the mirror surface = 25°.
• To Find:
  • The angle of reflection (r).
• Concept (Formula):
  • This is a common trap. The angle of incidence (i) is not the angle with the mirror; it is the angle with the normal.
  • The normal is an imaginary line perpendicular (at 90°) to the mirror surface.
  • Step 1: Find the angle of incidence: i = 90° - (Angle with the mirror)
  • Step 2: Use the First Law of Reflection: r = i.
• Solution:
  • First, we must calculate the correct angle of incidence (i).
  • i = 90° - 25°
  • i = 65°
  • Now, we use the First Law of Reflection (r = i).
  • Since i = 65°, then r = 65°.

Final Answer: The angle of reflection will be 65° (not 25°).

Question: If the angle of reflection for a ray of light is 50°, what is the total angle between the incident ray and the reflected ray?

Answer:

• Given:
  • The angle of reflection (r) = 50°
• To Find:
  • The total angle between the incident ray and the reflected ray.
• Concept (Formula):
  • Step 1: Use the First Law of Reflection (i = r) to find the angle of incidence.
  • Step 2: The total angle is the sum of the angle of incidence and the angle of reflection.
  • Total Angle = i + r
• Solution:
  • First, find the angle of incidence (i):
  • According to the law of reflection, i = r.
  • Since r = 50°, then i = 50°.
  • Now, find the total angle between the two rays:
  • Total Angle = i + r
  • Total Angle = 50° + 50° = 100°

Final Answer: The total angle between the incident ray and the reflected ray is 100°.

Question: Sonia is standing 5 meters in front of a large plane mirror. What is the distance between Sonia and her image?

Answer:

• Given:
  • Distance of the object (Sonia) from the mirror = 5 m.
• To Find:
  • The total distance between the object (Sonia) and her image.
• Concept (Formula):
  • A key property of an image formed by a plane mirror is that the object distance is equal to the image distance.
  • The image is formed as far "behind" the mirror as the object is "in front" of it.
  • Object Distance = Image Distance
  • Total Distance = (Object Distance) + (Image Distance)
• Solution:
  • First, find the distance of the image from the mirror:
  • Image Distance = Object Distance = 5 m.
  • Now, find the total distance between Sonia and her image:
  • Total Distance = (Sonia's distance to mirror) + (Image's distance to mirror)
  • Total Distance = 5 m + 5 m = 10 m

Final Answer: The distance between Sonia and her image is 10 meters.

Question: Two plane mirrors are placed perpendicular to each other (at an angle of 90°). If an object is placed between them, how many images will be formed?

Answer:

• Given:
  • The angle between the two mirrors (θ) = 90°
• To Find:
  • The number of images formed (n).
• Concept (Formula):
  • To find the number of images formed by two mirrors at an angle, we first calculate the value of m = 360° / θ.
  • If 'm' is an even integer (like 2, 4, 6), the number of images (n) is:
  • n = m - 1 or n = (360° / θ) - 1
• Solution:
  • First, calculate the value of m:
  • m = 360° / 90° = 4
  • The result, 4, is an even integer.
  • Now, apply the formula to find the number of images (n):
  • n = m - 1
  • n = 4 - 1 = 3

Final Answer: 3 images will be formed.

Question: A kaleidoscope uses three mirrors inclined at 60° to each other. How many images are formed by two of those mirrors (inclined at 60°)?

Answer:

• Given:
  • The angle between the two mirrors (θ) = 60°
• To Find:
  • The number of images formed (n).
• Concept (Formula):
  • We use the same formula as the previous problem: n = (360° / θ) - 1. This formula works when 360° / θ is an integer (both even and odd).
• Solution:
  • First, calculate the value of m = 360° / θ:
  • m = 360° / 60° = 6
  • The result, 6, is an even integer.
  • Now, apply the formula:
  • n = m - 1
  • n = 6 - 1 = 5

Final Answer: 5 images will be formed. This principle of multiple reflections is what creates the beautiful, complex patterns inside a kaleidoscope.

Question: A boy is in a barber's shop where two mirrors are placed parallel to each other. How many images of the boy will be formed?

Answer:

• Given:
  • Two mirrors are placed parallel to each other.
• To Find:
  • The number of images formed (n).
• Concept (Formula):
  • This is a special conceptual case. When two mirrors are parallel, the angle between them (θ) is 0°.
  • If we try to use the formula m = 360° / 0°, the result is undefined or infinity (∞).
• Solution:
  • When an object is placed between parallel mirrors, the image formed in the first mirror acts as a virtual object for the second mirror.
  • The image formed by the second mirror then acts as a new virtual object for the first mirror.
  • This process of reflection repeats back and forth, creating an image of an image of an image.

Final Answer: An infinite (∞) number of images will be formed. Each image will appear fainter and further "into" the mirror.

Question: A person is standing 3 meters from a plane mirror. If the person moves 1 meter backwards (away from the mirror), what will be the new distance between the person and their image?

Answer:

• Given:
  • Initial object distance = 3 m.
  • The person (object) moves 1 m away from the mirror.
• To Find:
  • The new total distance between the person and the image.
• Concept (Formula):
  • Total Distance = (New Object Distance) + (New Image Distance)
  • And, New Image Distance = New Object Distance
• Solution:
  • First, find the new object distance:
  • New Object Distance = Initial Distance + Distance Moved
  • New Object Distance = 3 m + 1 m = 4 m
  • Now, find the new image distance:
  • Since Image Distance = Object Distance, the New Image Distance is also 4 m.
  • Finally, find the total distance between the person and their image:
    • Total Distance = (New Object Distance) + (New Image Distance)
    • Total Distance = 4 m + 4 m = 8 m

Final Answer: The new distance between the person and their image will be 8 meters.

HOTS Important Questions and Answers: Class 8 Light

Question 1: The Ambulance Mystery

Question: Why is the word "AMBULANCE" often written in large letters as a mirror image (i.e., reversed) on the front of the vehicle?

Answer:

This is a clever real-world application of a property of plane mirrors called lateral inversion.

• Lateral inversion is the phenomenon where the left side of an object appears to be the right side in its mirror image, and vice-versa.
• The driver of a car ahead of the ambulance will see the vehicle in their rear-view mirror.
• Because the rear-view mirror is a plane mirror, it will laterally invert the text written on the front of the ambulance.
• By writing the word as a mirror image, the mirror "flips" it back, allowing the driver to read the word "AMBULANCE" correctly and immediately. This helps them understand the emergency and give way quickly.

Question 2: Adjusting to the Dark

Question: When you come from a brightly lit area (like sunlight) into a dark room (like a movie theater), why can't you see clearly for a few minutes? Explain the parts of the eye involved.

Answer:

This delay in vision is called dark adaptation, and it involves two main parts of your eye: the pupil and the retina (rods and cones).

1. Pupil and Iris: In bright light, the iris (the colored part of the eye) makes the pupil (the black hole) very small. This is done to limit the amount of light entering the eye and protect the retina. When you enter a dark room, the pupil needs to widen (dilate) to let in as much light as possible. This adjustment by the iris takes a few seconds.
2. Rods and Cones: This is the more important reason. The retina has two types of photoreceptor cells: cones and rods.
   • Cones work in bright light and see color. They adapt quickly.
   • Rods work in dim light and see shades of grey. They are bleached out and inactive in bright sunlight. When you enter the dark, the rods must slowly "recharge" and become sensitive again. This chemical process can take several minutes.

Therefore, you can't see well until your pupils have fully dilated and your rods have regained their sensitivity to dim light.

Question 3: The Rotating Mirror (Advanced HOTS)

Question: An incident ray of light strikes a plane mirror. If the incident ray is kept fixed, but the mirror is rotated by an angle θ (theta), by what angle does the reflected ray rotate?

Answer:

The reflected ray will rotate by an angle of 2θ (two times theta).

Explanation:

This is a standard property of reflection. While the full proof involves geometry, the concept is as follows:

• Initial State: Let the angle of incidence be i. The angle of reflection is also i.
• Rotation: When you rotate the mirror by an angle θ, the normal to the mirror also rotates by the same angle θ.
• New State: The incident ray has not moved, but the normal has. The new angle of incidence is now (i + θ).
• According to the law of reflection, the new angle of reflection must also be (i + θ).
• The Result: The total change in the reflected ray's direction comes from both the change in the normal's position (θ) and the change in the reflection angle relative to the new normal (θ). The total rotation is θ + θ = 2θ.

Example: If you rotate the mirror by 10°, the reflected ray will move by 20°.

Question 4: The 40-Degree Trap

Question: A ray of light is incident on a plane mirror, making an angle of 40° with the reflected ray. What is the angle of incidence?

Answer:

Given: The total angle between the incident ray and the reflected ray = 40°.

Concept:

1. The First Law of Reflection states: Angle of Incidence (i) = Angle of Reflection (r).
2. The total angle given (40°) is the sum of the angle of incidence and the angle of reflection.
3. Total Angle = i + r

Solution:

We know i + r = 40°

Since i = r, we can replace r with i in the equation:

i + i = 40°

2i = 40°

i = 40° / 2

i = 20°

Final Answer: The angle of incidence is 20°. (And the angle of reflection is also 20°).

Question 5: The Moving Image

Question: You are standing 4 meters away from a plane mirror. If you run towards the mirror at a speed of 2 meters per second (m/s), what is the speed at which your image appears to be moving towards you? (This is the relative speed between you and your image).

Answer:

The image will appear to be moving towards you at a speed of 4 m/s.

Explanation:

• Property of Plane Mirrors: The image is always as far behind the mirror as the object is in front of it.
• Your Speed: You (the object) are moving towards the mirror at 2 m/s.
• Image's Speed: Because the image must always be the same distance from the mirror, your image must also be moving towards the mirror from the other side at the exact same speed, which is 2 m/s.
• Relative Speed: You are moving towards your image at 2 m/s, and your image is moving towards you at 2 m/s. To find the relative speed (the speed at which the distance between you is closing), you must add the two speeds.
• Relative Speed = (Your Speed) + (Image's Speed)
• Relative Speed = 2 m/s + 2 m/s = 4 m/s.

Therefore, the distance between you and your image is closing at a rate of 4 meters per second.

Light Class 8 Diagram-Based Important Questions

This is a high-value section, as drawing and labeling diagrams is a guaranteed part of your exam. Practice these to score full marks. This section targets diagram based questions class 8 light.

Q1: Draw a neat, labeled diagram of the human eye.

Answer:

To answer this question, you must draw a cross-section of the human eye and label all its important parts. The diagram should be clean, and the labels should be clearly written, pointing to the correct part.

Key Labels to Include:

• Cornea
• Iris
• Pupil
• Lens (Crystalline Lens)
• Retina
• Optic Nerve
• Ciliary Muscles
• Blind Spot

Q2: Draw a ray diagram showing the laws of reflection.

Answer:

This diagram demonstrates the two laws of reflection. You must draw a flat, reflective surface (a plane mirror), an incoming ray (incident ray), and a bouncing ray (reflected ray). The "Normal" is the most important part to draw correctly.

Key Labels to Include:

• Plane Mirror (or Reflecting Surface)
• Incident Ray (with an arrow pointing towards the mirror)
• Reflected Ray (with an arrow pointing away from the mirror)
• Normal (a dotted line at 90° to the mirror)
• Angle of Incidence (i) - (The angle between the Incident Ray and the Normal)
• Angle of Reflection (r) - (The angle between the Reflected Ray and the Normal)
• Point of Incidence

Q3: Draw a diagram to show the dispersion of white light by a glass prism.

Answer:

This diagram shows how white light splits into its seven component colors. You need to draw a triangular glass prism and show a single beam of white light entering one side and a full spectrum of seven colors exiting the other.

Key Labels to Include:

• Glass Prism
• Incident Ray (labeled as "White Light")
• Refracted Ray (inside the prism)
• Emergent Rays (splitting into 7 colors)
• Spectrum (The band of 7 colors)
• Label the colors in the correct order: Red (top), Orange, Yellow, Green, Blue, Indigo, Violet (bottom) - (VIBGYOR from bottom to top).

Q4: Label the parts of a candle flame.

Answer:

This question is also related to the chapter "Combustion and Flame" but is often asked alongside "Light" due to the visual nature of the flame. You must draw a simple candle flame and label its three main zones.

Key Labels to Include:

• Outer Zone (Blue, Hottest part, Complete combustion)
• Middle Zone (Yellow, Luminous part, Partial combustion)
• Inner Zone (Black, Unburnt wax vapors, Least hot)
• Wick

What is the difference between Regular and Diffused Reflection?

Answer: The difference between regular and diffused reflection is as follows:

What is dispersion of light?

Answer: Dispersion of light is the phenomenon of splitting white light into its seven constituent colors (Violet, Indigo, Blue, Green, Yellow, Orange, Red - VIBGYOR) when it passes through a transparent medium like a glass prism. A rainbow is a natural example of dispersion, where tiny water droplets in the air act as prisms.