Activities 10.2 and 10.3 — Characteristics of Images in Spherical Mirrors — "Light: Mirrors and Lenses"

1. 14 marksCuriosity Grade 8, Chapter 10, page 155

   Describe Activity 10.3 — the set-up and the questions it asks you to record at each object distance.

   Hint. Two mirrors, one object, two distances, and the same four questions each time.

   The set-up. Place a concave mirror and a convex mirror side by side, upright, on a table. Place a small object 3–4 cm in front of them (Fig. 10.5a) and record: What kind of images do you see in each mirror? Are the images of the same size as the object? Are they erect? Do you see lateral inversion in the images?

   Then move the object farther away (Fig. 10.5b) and ask the same four questions again, watching for change.

   Finally, repeat with each mirror individually and draw conclusions from comparing all the observations.

   ✦ Asking the identical four questions at both distances is what makes the comparison fair. If a different set of questions were used each time, you could never be sure whether an apparent change was a real effect of distance or just a difference in what was being looked for. Since the object, the questions and the mirrors are all held fixed except for one variable — the distance — any change you observe can be attributed to that distance alone.

2. 24 marksCuriosity Grade 8, Chapter 10, page 156

   State the full set of results from Activity 10.3 for the concave mirror.

   Hint. Small distance and large distance give two different answers — both size and orientation change.

   In the concave mirror, when the object is placed close to the mirror, the image is erect but larger than the object in size, that is, enlarged. However, when the object is moved farther away, the image becomes inverted. Initially, the image is enlarged in size and then keeps getting smaller.

   Object distance	Orientation	Size
   Close	Erect	Enlarged
   Farther	Inverted	Starts enlarged, then shrinks

   ✦ Two separate things change with distance, and it is easy to report only one. The orientation flips from erect to inverted at some point as the object recedes; independently, the size grows at first and then falls as the distance keeps increasing. Since both descriptions are needed to match what the chapter actually reports, an answer that only says 'it gets smaller' or only says 'it becomes inverted' has captured half the picture.

   Lateral inversion is seen throughout, in every mirror the chapter discusses — that fact does not distinguish the concave mirror from the others and is treated separately below.

3. 33 marksCuriosity Grade 8, Chapter 10, page 156

   State the full set of results from Activity 10.3 for the convex mirror, and contrast it with the concave mirror's behaviour.

   Hint. Only one of the two mirrors ever flips its image upside down.

   In case of a convex mirror, the image is always erect and smaller than the object, that is diminished. However, the size of the image decreases slightly as the object is moved away from the convex mirror.

   	Convex mirror	Concave mirror
   Orientation	Always erect	Erect close, inverted farther
   Size	Always diminished; shrinks slightly further with distance	Enlarged close, shrinks with distance, can pass through equal to inverted

   ✦ The word always is doing real work in the convex-mirror sentence, and it is the chapter's own word. Whatever the object's distance, a convex mirror never inverts the image and never enlarges it — since there is no distance at which its behaviour changes in kind, only in degree (a little smaller, then a little smaller still). This is exactly why convex mirrors are trusted for consistent, predictable viewing — a side-view mirror that sometimes inverted the traffic behind you would be useless.

4. 43 marksCuriosity Grade 8, Chapter 10, page 156

   What is lateral inversion, and how does the chapter say it behaves across plane, concave and convex mirrors?

   Hint. One property is shared by every mirror in the chapter; the others are not.

   Lateral inversion is the left-right flip of an image — your left hand appears as the image's right hand.

   Lateral inversion of the image is seen in all three types of mirrors.

   This is the one property Activity 10.3 finds to be constant across the board, in contrast to size and orientation, which change with mirror type and distance. A plane mirror, a concave mirror close up, a concave mirror far away, and a convex mirror at any distance all show lateral inversion.

   ✦ Do not confuse lateral inversion with the erect-versus-inverted distinction, which the chapter keeps carefully separate. 'Erect or inverted' is about whether the image is turned upside down — top-to-bottom; lateral inversion is about left-right. Since a concave mirror's image can go from erect to fully inverted as the object recedes, while lateral inversion is present in both cases, the two properties clearly measure different things and both must be reported when a question asks for the full description of an image.

5. 54 marksCuriosity Grade 8, Chapter 10, page 156

   A student says: 'We can tell whether a mirror is plane, concave, or convex just by looking at the images of an object formed in them.' Is this a fair conclusion from Activity 10.3? Justify.

   Hint. Check whether the three mirrors leave genuinely distinguishable fingerprints.

   Yes — and this is exactly the chapter's own conclusion, put in a character's mouth immediately after the activity:

   I just got an idea. We can also identify whether a mirror is plane, or concave, or convex by looking at the images of an object formed in them!

   The justification is that the three mirrors leave three different, testable signatures.

   Mirror	Signature
   Plane	Always erect, always same size as the object, at every distance
   Concave	Erect and enlarged close up; becomes inverted farther away
   Convex	Always erect, always diminished, at every distance

   ✦ The convex-versus-plane comparison is the one that most depends on measuring size carefully. Both are always erect, so orientation alone cannot separate them — since only a convex mirror consistently gives an image smaller than the object, size is the deciding test between those two. Because each mirror's pattern is genuinely distinct from the other two, the student's conclusion holds up, and it is the entire method Activity 10.2 already used from the side view, now confirmed from the front by the images themselves.

6. 63 marksCuriosity Grade 8, Chapter 10, page 156

   Give two real-world uses of the concave mirror and explain why its enlarging property suits each.

   Hint. Both uses depend on the same close-up behaviour Activity 10.3 measured.

   Two of the chapter's own examples:

   The reflectors of torches, headlights of cars and scooters are concave in shape.

   A dental mirror used by a dentist for inspecting teeth ... is a concave mirror which provides an enlarged view of teeth when held close to the teeth inside the mouth.

   Why concave suits the dentist's mirror. A dentist works at very close range inside a small mouth, and Activity 10.3 showed that when the object is placed close to the mirror, the image is erect but larger — exactly the enlarged, right-way-up view a dentist needs to spot a problem on a tooth's surface.

   ✦ The torch and headlight use is a slightly different application of the same mirror, working the reverse way round: instead of viewing an enlarged image of something small and close, a bulb is placed at the mirror's focus so the concave shape sends its light out as a controlled beam. Since the chapter classes both under one shape, the useful property being exploited differs by use — magnification for the dentist, beam control for the torch — but the underlying mirror is the same concave curve.

7. 73 marksCuriosity Grade 8, Chapter 10, page 157

   Give three real-world uses of the convex mirror and explain what property of the convex mirror each depends on.

   Hint. All three lean on the same fact — a wider field of view in a smaller image.

   Three of the chapter's examples, and the property behind each:

   These mirrors are convex. They always form an erect image of the traffic behind and smaller than the actual vehicles. Also ... it provides a much wider area of the road behind. — side-view mirrors

   Such convex mirrors are installed at road intersections or sharp bends to provide drivers from both sides the visibility of the other side and prevent collisions. — road safety mirrors

   Convex mirrors are also installed in big stores to monitor a large area to deter thefts. — store surveillance mirrors

   ✦ All three uses are variations on the same trade: a smaller image in exchange for a wider view. Since the convex mirror is curved outside, it provides a much wider area — a side-view mirror shrinks the cars behind you so it can fit far more of the road into the same small glass; the same shrinking-for-width trade lets one mirror at a bend show traffic from both directions, and lets one mirror in a shop cover an entire aisle. Because the property is identical in every case, recognising it once lets you explain all three uses without treating them as separate facts to memorise.

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.