This MCQ module is based on: Plane and Curved Mirrors
TOPIC 35 OF 50
Plane and Curved Mirrors
🎓 Class 8
Science
CBSE
Theory
Ch 10 — Force and Pressure
⏱ ~27 min
🌐 Language: [gtranslate]
🧠 AI-Powered MCQ Assessment
▲
Myaischool Lt Science Assessment
▲
[myaischool_lt_science_assessment grade_level="class_8" science_domain="physics" difficulty="basic"]
Probe and Ponder
Stand in front of a well-polished steel spoon. Look at the front (inner, hollow) side — you appear upside-down. Flip it around and gaze at the back (bulging) side — now you are tiny, upright and shrunken. A single piece of metal, two astonishing images! Why?
- Why does a plane mirror never enlarge or shrink us, but a spoon does?
- Which mirror would a dentist choose to look at the back of your tooth — flat, hollow or bulging?
- Why do vehicle side-mirrors carry a little warning "Objects in mirror are closer than they appear"?
- How does the same science that gives us mirrors also build cameras, spectacles and microscopes?
In this chapter we return to light — the quick, straight-travelling traveller that brings us nearly all the information we receive about the world — and discover how cleverly shaped mirrors and transparent lenses bend it to our advantage.
10.1 A Quick Reminder: What a Plane Mirror Does
A plane mirror is simply a flat, polished surface that reflects light in a very orderly way. When you stand before it, light from every point of your face travels to the mirror and bounces back at exactly the same angle at which it arrived — this is the law of reflection: angle of incidence equals angle of reflection, and both lie in the same plane as the normal (the imaginary line drawn perpendicular to the mirror at the point of incidence).
What the Image Looks Like
The image formed by a plane mirror has four steady personalities:
- Virtual — you can't catch it on a screen; it only appears to be behind the mirror.
- Erect — head-up, not inverted.
- Same size as the object.
- Laterally inverted — your right hand appears as the image's left hand.
Lateral Inversion: the swapping of left and right in a mirror image. Try writing AMBULANCE on a card and hold it before a mirror — you'll see why the word is printed reversed on the front of real ambulances!
10.2 Meet the Curved Family — Concave & Convex Mirrors
Polish the inside of a shiny metal bowl and you have a concave mirror. Polish the outside and you get a convex mirror. These are the two members of the curved (spherical) mirror family.
Important Points on a Curved Mirror
- Pole (P) — the centre of the mirror's surface.
- Centre of Curvature (C) — the centre of the sphere of which the mirror is a slice.
- Focus (F) — the point on the principal axis where parallel rays meet (concave) or appear to come from (convex). The distance PF is the focal length (f).
- For small spherical mirrors, \(f \approx \dfrac{R}{2}\), where R = PC is the radius of curvature.
How They Reflect Parallel Rays
10.3 Images in Concave and Convex Mirrors — A First Look
Concave Mirror — Two Personalities
A concave mirror is more interesting than a plane mirror because the kind of image it forms depends on the distance of the object.
- When the object is very close to the mirror (closer than the focus), the image is virtual, erect and enlarged — like your face in a shaving or make-up mirror.
- When the object is far from the mirror (beyond the focus), the image becomes real and inverted — this can even be caught on a piece of paper!
Convex Mirror — Always the Same
A convex mirror is predictable. No matter where you place the object, it always gives a virtual, erect and diminished (smaller) image. That is exactly why it is chosen as the outside mirror of cars, scooters and buses — small image means a wide field of view.
| Feature | Plane Mirror | Concave (far object) | Convex |
|---|---|---|---|
| Image type | Virtual | Real | Virtual |
| Orientation | Erect | Inverted | Erect |
| Size | Same as object | Usually smaller | Smaller (diminished) |
| Field of view | Normal | Narrow | Very wide |
🥄 Activity 10.1 — The Two Faces of a Shiny Spoon
You will need: one well-polished steel spoon, a bright window or lamp.
- Hold the spoon so that its inner (hollow) side faces you. Keep it close — about 5 cm from your nose.
- Note what you see. Now slowly move the spoon further away.
- Flip the spoon and look at your face in the outer (bulging) side. Try it at different distances.
🔍 Predict: Does any side ever turn your face upside-down? Which side never enlarges your face? Why?
Inner (concave) side — close: Face appears erect and bigger — a virtual enlarged image.
Inner (concave) side — far: Face suddenly flips and becomes upside-down — a real inverted image.
Outer (convex) side — any distance: Face is always erect and smaller — a virtual diminished image.
The spoon is a natural classroom — inside is a concave mirror, outside is a convex mirror!
10.4 Where Do We Meet These Mirrors?
Dentist's & Shaving Mirror
Concave mirror held close gives a large, erect view of a tooth or a chin.
Vehicle Side Mirror
Convex mirror gives a wider view of the road behind — small image, big area.
Torch & Headlight
Concave mirror turns a tiny bulb's light into a powerful parallel beam.
Solar Cooker
Large concave mirrors concentrate sunlight at a cooking vessel placed at the focus.
🎯 Competency-Based Questions
Rhea is going on a long trip in a car. She notices different mirrors used in and on the car — a flat mirror inside on the windscreen, and curved mirrors on the two sides. She also sees a huge, bulging mirror fitted at a sharp turn on the hill road.
Q1. L1 Remember State the two key properties of the image in a plane mirror other than its being virtual.
Answer: The image is (i) erect (same way up as the object) and (ii) of the same size as the object. It is also laterally inverted — left and right are swapped.
Q2. L2 Understand Why is the huge bulging mirror fitted at a hill-road turn a convex mirror and not a plane one?
Answer: A convex mirror always makes the image smaller and therefore fits a much wider slice of the road into one mirror. A plane mirror of the same size would only show a narrow view. Drivers need to spot vehicles coming from the opposite side of the bend, so a wide field of view is essential.
Q3. L3 Apply Rhea writes "HELP" with her finger on a dusty car window and views it in the rear-view mirror. Will she read "HELP" or something else? Explain.
Answer: The rear-view mirror laterally inverts the message, so "HELP" will appear mirror-reversed. That is exactly why emergency words on ambulances and police vans are printed reversed on their fronts — drivers ahead see them the right way round in their rear-view mirrors.
Q4. L4 Analyse A shopkeeper fits a convex mirror in the corner of his shop rather than a concave one. Analyse the reason.
Answer: A convex mirror provides a very wide field of view with small, erect images, so the shopkeeper can watch every aisle of the shop from a single spot. A concave mirror would magnify a small region but miss most of the shop and even invert images for distant objects — useless for surveillance.
Q5. L5 Evaluate A friend claims: "All curved mirrors enlarge things, that is why they are called magnifying mirrors." Evaluate this statement.
Answer: The statement is incorrect. Only a concave mirror, when the object is closer to it than the focus, produces an enlarged virtual image. A convex mirror always gives a diminished image and a concave mirror with a faraway object also gives a smaller (but inverted and real) image. The term "magnifying" therefore applies only to a particular use of a concave mirror.
🔗 Assertion–Reason Questions
Assertion (A): The image formed by a plane mirror is virtual.
Reason (R): The reflected rays only appear to meet behind the mirror; they never actually meet there.
Answer: A. A virtual image is one formed by rays that only seem to meet — exactly what happens behind a plane mirror.
Assertion (A): A convex mirror is used as the side mirror of vehicles.
Reason (R): It always forms an enlarged virtual image.
Answer: C. A is true, but R is false — a convex mirror always gives a diminished (smaller) image. Its usefulness comes from the wide field of view, not from enlargement.
Assertion (A): A concave mirror can form both virtual and real images.
Reason (R): The nature of the image depends on the position of the object relative to the focus.
Answer: A. Object between pole and focus → virtual, erect, enlarged; object beyond the focus → real, inverted image.
AI Tutor
Science Class 8 — Curiosity
Ready