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Light: Mirrors and Lenses – Class 8 Science notes, important questions and MCQs

NCERT Class 8 Science, chapter 10. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Light reflects from mirrors and bends through lenses. Plane, concave and convex mirrors and lenses form different images used in daily life.

Reflection

Laws: angle of incidence = angle of reflection; incident ray, reflected ray and normal lie in one plane.
Plane mirror: image is virtual, erect, same size, as far behind as the object is in front, laterally inverted.
Concave mirror (torches, shaving); convex mirror (rear-view, wider view).

Lenses and the eye

Convex lens converges light (magnifying glass, camera, spectacles for long sight).
Concave lens diverges light (spectacles for short sight).
The eye lens forms an image on the retina; white light splits into seven colours through a prism (dispersion).

Key terms

Lateral inversion: left and right swapped in a mirror image
Virtual image: image that cannot be obtained on a screen
Dispersion: splitting of white light into colours

Formulas

Angle of incidence = angle of reflection
Colours of the spectrum: VIBGYOR

Important questions with answers

State the two laws of reflection.2 marks

The angle of incidence equals the angle of reflection; the incident ray, the reflected ray and the normal all lie in the same plane.

Give one use each of a concave mirror and a convex mirror.3 marks

Concave: shaving or make-up mirror, dentist's mirror, torch reflector. Convex: rear-view mirror of vehicles, security mirrors in shops.

Compare concave and convex mirrors and lenses by the images they form, and explain how white light is split by a prism.5 marks

Concave mirror and convex lens can form real, inverted images (on a screen) when the object is far, and enlarged, erect virtual images when the object is very close. Convex mirror and concave lens always form virtual, erect and diminished images. A prism splits white light into seven colours (VIBGYOR) because each colour bends by a different amount on entering and leaving the glass: violet bends most and red least. This is called dispersion; a rainbow forms the same way in raindrops.

Quick revision

Plane mirror image = same size, laterally inverted.
Convex lens = converging; concave lens = diverging.
Prism splits white light.

Exam tips

AMBULANCE is written in reverse on vehicles so drivers read it correctly in mirrors.
Convex mirror always gives a small, erect image — safe for seeing more traffic.

Practice MCQs

The image in a plane mirror is
1. real and inverted
2. virtual and erect
3. real and erect
4. smaller
Show answer
Answer: (b) virtual and erect. Virtual, erect, same size.
Rear-view mirrors are
1. concave
2. convex
3. plane
4. cylindrical
Show answer
Answer: (b) convex. Wider field of view.
If the angle of incidence is 35°, the angle of reflection is
1. 55°
2. 35°
3. 70°
4. 145°
Show answer
Answer: (b) 35°. They are equal.
A magnifying glass is a
1. concave lens
2. plane mirror
3. convex lens
4. prism
Show answer
Answer: (c) convex lens. Convex lens.
Rear-view mirrors in vehicles are
1. concave
2. convex
3. plane only
4. cylindrical
Show answer
Answer: (b) convex. Wider field of view.
A person stands 2 m in front of a plane mirror. The distance between the person and the image is
1. 2 m
2. 0 m
3. 1 m
4. 4 m
Show answer
Answer: (d) 4 m. Image is 2 m behind.
Why is "AMBULANCE" written in reverse on ambulances?
1. for decoration
2. to confuse drivers
3. so it reads correctly in rear-view mirrors
4. it is a rule for all vehicles
Show answer
Answer: (c) so it reads correctly in rear-view mirrors. Lateral inversion.
A magnifying glass is a
1. concave lens
2. convex lens
3. plane mirror
4. prism
Show answer
Answer: (b) convex lens. Converging lens.

All chapters of Class 8 Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.