NCERT Solutions Curiosity Chapter 11 Interdisciplinary projects — Exploratory Projects

Book page 167 & 168 Updated on2026-09-05

Q1.

Have you ever seen a firefly where you live? If no, ask your elders if fireflies were seen earlier in your region. If yes, find out the reasons for their not being seen anymore. Develop a story about it.

Answer

How to do this project: talk to two or three elders of your family or locality. Ask them where and in which months they used to see fireflies, whether the number has fallen, and what has changed in that place since — new street lights, buildings, cutting of trees, use of pesticides. Note their answers, then weave them into a short story.

Reasons usually found for the disappearance of fireflies:

Light pollution — bright street lights and hoardings drown out the firefly's own flashes, so males and females can no longer find each other.
Loss of forest and grass cover — fields, hedges and moist leaf litter where the larvae live are cleared for houses and roads.
Pesticides and insecticides — these kill fireflies and also the snails and small insects their larvae feed on.
Excessive tourism and noise in firefly-watching areas, and drying up of ponds and streams nearby.

Sample answer (a short story): “My grandmother says that when she was ten, the guava orchard behind our house would light up on July nights with hundreds of tiny green lamps. The children called them jugnu and caught them in glass jars, then let them go before sleeping. Today a tall pole light stands where the orchard was. The night never becomes dark, and the jugnu have not come back for many years. Grandmother says the fireflies did not go away — we took away their darkness.” End your story with one thing your family will do, such as switching off the outdoor light at night.

Q2.

Repeat Activity 11.4, but this time cover the face of the torch with a coloured transparent paper and observe the colour of the shadow. Repeat this using transparent paper of different colours. Report your conclusions.

Answer

What you will observe:

Colour of paper on the torch	Colour of the lit part of the screen	Colour of the shadow
Red	Red	Dark (black)
Green	Green	Dark (black)
Blue	Blue	Dark (black)
Yellow	Yellow	Dark (black)

Conclusions: The coloured paper changes the colour of the light, and therefore the colour of the bright region around the shadow. The shadow itself stays dark in every case — its shape and size do not change either. A shadow has no colour of its own, because it is only a place where no light has reached.

Try This: Use two torches, one covered with red paper and the other with green, placed a little apart. Each throws its own shadow, and each shadow is lit by the other torch — so you get one reddish and one greenish patch instead of black. A beautiful result to show your class.

Q3.

A plane mirror forms only a single image of an object. But what will happen if two or more mirrors are kept at an angle with each other or parallel to each other? Find out by placing two mirrors as shown in Fig. 11.21.

Answer

Two mirrors give many images, because each mirror also forms images of the images made by the other — reflections of reflections. The number depends on the angle between the mirrors.

Number of images = (360° ÷ angle between the mirrors) − 1

Angle between the two mirrors	Number of images seen
180° (in one straight line)	1
120°	2
90° (as in Fig. 11.21)	3
60°	5
45°	7
Parallel, facing each other	A very long line of images, seemingly endless

Place a bottle cap between two mirrors joined at 90°, exactly as in Fig. 11.21, and count — you will see three images along with the cap itself. Close the mirrors to 60° and the count rises to five.

Why it happens: The first mirror forms an image of the cap. That image acts as an object for the second mirror, which forms an image of it, and so on. Each round of reflection adds more images, until the mirrors run out of room to reflect. When the mirrors are parallel, the reflections never run out — they only get fainter and fainter, because a little light is lost at every reflection.

Did you know? The kaleidoscope of Section 11.8.2 uses three mirrors at 60° to each other, which is why it fills with so many symmetric patterns.

Q4.

You are given a small piece of a plane mirror. Can this piece form an image of an object much larger than the mirror, like a large tree? Think and predict. Then carry out the activity.

Answer

Prediction and result: yes, it can. Take a small piece of mirror outdoors, hold it at arm's length and move your eye about behind it — you can see the whole tree in it, bit by bit, and from a suitable position the whole tree at once.

Why it happens: The size of the image does not depend on the size of the mirror. Light from every part of the tree falls on the small mirror and is reflected; the mirror forms a complete image of the tree behind itself, of the same size as the tree. Your eye, however, can only receive the rays that actually pass through the small piece — so the mirror acts like a little window on to that image. Move your eye or the mirror and you see through a different part of the window.

Check it yourself: Look at your face in a small mirror held close to your eye — you see only your eye. Now stretch your arm out; the same little mirror shows your whole face. The farther the mirror, the wider the view it gives.

Was this helpful? Report an error