Activity 10.1 — What Are Spherical Mirrors? — "Light: Mirrors and Lenses"

1. 13 marksCuriosity Grade 8, Chapter 10, page 153

   Describe Activity 10.1 and its two main observations.

   Hint. One spoon, two sides, two very different images.

   The activity. Hold a shiny metallic spoon's curved surface close to your face and look at your reflection. Slowly move the spoon away and watch the image change. Flip the spoon and repeat on the other side.

   The two observations.

   When you looked at the inner side of the spoon which is curved inwards, you must have observed that the image was inverted. When you looked at the outer side of the spoon which bulges outwards, the image of your face was erect but smaller in size.

   Side of the spoon	Curve	Image
   Inner (concave)	Inward	Inverted
   Outer (convex)	Outward	Erect, smaller

   ✦ One everyday object does the whole job of introducing two new kinds of mirror. A spoon is not specially made for optics, so its inner and outer surfaces stand in for what a proper concave and convex mirror will do — which is exactly why this simple activity opens the chapter rather than a diagram.

2. 23 marksCuriosity Grade 8, Chapter 10, page 153

   Define a spherical mirror. Why is it called 'spherical' when it looks like a curved dish rather than a ball?

   Hint. The chapter's own name for the imaginary object it comes from.

   Spherical mirrors are a common type of curved mirrors which are shaped like a part of a hollow glass sphere. Mirrors, whose reflecting surfaces are spherical are called spherical mirrors.

   Why the name, despite the shape. A spherical mirror is not a whole sphere — it is a small curved piece whose surface matches part of the surface of an imagined hollow sphere, the way a single tile from the inside of a ball would still be curved exactly like the ball. Since every point on that piece lies on the surface of the same imaginary sphere, the mirror is correctly called spherical even though what you hold in your hand looks like a shallow dish.

   ✦ The outline is a separate fact worth keeping distinct from the curve. The outline of the surface of the mirror is circular — that is about the edge of the mirror as seen face-on, while 'spherical' describes the curve of the surface itself. A round dinner plate has a circular outline too, but it is flat, not spherical — so the two words are not describing the same thing.

3. 33 marksCuriosity Grade 8, Chapter 10, page 154

   Define concave and convex mirrors, and state how the non-reflecting surface is shown in their schematic representations.

   Hint. One curves toward you, one curves away — and the diagrams mark the back of the mirror consistently.

   A spherical mirror, which has a reflecting surface that curves inwards, is called a concave mirror.

   A spherical mirror which has a reflecting surface that curves outwards is called a convex mirror.

   In the representation of both the mirrors, the non-reflecting surface of the mirror is shown as shaded.

   	Concave	Convex
   Reflecting surface curves	Inwards	Outwards
   In Activity 10.1	Inner side of the spoon	Outer, bulging side of the spoon

   ✦ The shading is a drawing convention, not a physical feature of the mirror itself. It marks which side is the back — the side you do not look into — so that a reader of the diagram never has to guess which curved surface is doing the reflecting. Since a schematic is meant to stand in for an experiment you cannot always perform, this convention is what lets you read Fig. 10.2b and 10.3b correctly without the spoon in your hand.

4. 44 marksCuriosity Grade 8, Chapter 10, page 154

   How are spherical mirrors actually manufactured? Explain why the 'A step further' box says they are not made by slicing a hollow glass sphere, despite looking like part of one.

   Hint. There are two different mental pictures here, and only one is the manufacturing process.

   The shape of a spherical mirror is such that it can be thought of as a part of an imaginary hollow sphere. However, remember that spherical mirrors are not made by slicing a hollow glass sphere. Instead, they are created by grinding and polishing a flat glass piece into a curved surface.

   Why the distinction matters. 'Part of a hollow sphere' is a useful way to describe the shape mathematically — every point matches a sphere's surface. It is not a description of how the mirror is manufactured. Confusing the two would lead you to imagine an actual glass ball being cut apart, which is not what happens in a workshop.

   ✦ And the coating decides which kind of mirror results, not the glass shape by itself:

   Reflective coating applied on…	Result
   The outer curved surface	A concave mirror — you look into the near, uncoated inner surface, and the coating behind it reflects
   The inner curved surface	A convex mirror — you look at the coated outer bulge

   So a single piece of ground and polished glass could become either kind of mirror, depending only on where the reflective aluminium layer is placed.

5. 53 marksCuriosity Grade 8, Chapter 10, page 155

   Describe Activity 10.2. How can you tell whether a mirror is concave or convex just by looking at it from the side?

   Hint. The trick is where you put your eye, not the mirror.

   The activity. Place a concave and a convex mirror on a table with their reflecting surfaces facing upwards. View them from the side, with your eye level with the mirrors, so you can see the profile of the curve.

   Fig. 10.4: Identifying concave and convex mirrors from their side view.

   What you see. A concave mirror's reflecting surface dips down in the middle, like the inside of a shallow bowl viewed from its rim. A convex mirror's reflecting surface bulges up in the middle, like the outside of a dome.

   ✦ Looking straight down at the mirrors would not show this at all — from directly above, both a concave and a convex dish can look like nothing more than a circular disc. Since the curve is only visible edge-on, the eye has to be brought down to the level of the mirror's rim before the dip or the bulge becomes obvious, which is exactly the instruction Activity 10.2 gives.

6. 63 marksCuriosity Grade 8, Chapter 10, pages 153-154

   A flat piece of aluminium foil, gently pressed into a shallow dent with a thumb, is held up as a mirror. Would this be concave or convex from the side you pressed?

   Hint. Think about which side of a spoon's inner curve the spoon's own concavity comes from.

   From the side you pressed — the side where the dent goes in — it would behave as a concave mirror.

   Pressing a thumb into a flat sheet creates a shallow inward curve on that side, exactly the shape of the inner side of the spoon in Activity 10.1, whose reflecting surface curves inwards. The chapter's own definition applies directly: a spherical mirror, which has a reflecting surface that curves inwards, is called a concave mirror.

   ✦ And the very same dent, seen from the other side of the foil, is a convex surface — it bulges outward there, just as the outer side of the spoon does. Since concave and convex describe the direction a single curved surface faces, one physical dent can be described either way depending on which face you are looking at, exactly as the spoon has one shape and two names for its two sides.

   A limit worth naming honestly. Crumpled foil is not a proper spherical mirror and would give a distorted, uneven image rather than the clean behaviour Activities 10.3, 10.6 and 10.9 describe for a true spherical surface — the direction of curvature can still be identified, even if the image it gives would be far from ideal.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8, Chapter 10 (hecu110.pdf), Reprint 2026-27, pages 152-169. Questions are referenced from the NCERT textbook for identification.