NCERT Solutions Curiosity Chapter 11 .2 Does Light Travel in a Straight Line? — Activity 11.1: Let us investigate
Book page 15511 Updated on2026-09-05
Q1.
Move one of the matchboxes slightly to a side or up and down. Are you able to obtain the light spot on the screen now?
Answer
No. The bright spot disappears from the screen the moment one of the three holes moves out of the line.
Light from the torch reaches the screen only while the three holes lie along one straight line.
Why it happens: Light from the torch can only go straight. As long as the three holes are on one straight line, that straight path is open and the light reaches the screen. Shifting one box makes its hole step out of the path, the cardboard of that box blocks the light, and the screen goes dark. Light cannot bend around the box to find the next hole.
Check it yourself: Bring the box back into line very slowly. The spot reappears exactly when the three holes and the torch bulb line up — nothing else about the set-up has changed.
Q2.
Can we somehow check it in some other way?
Answer
Yes. The straight-line travel of light can be checked in several simple ways:
Straight and bent pipe (Activity 11.2) — a candle flame is seen through a straight pipe but vanishes as soon as the pipe is bent.
Laser beam in milky water (Dive Deeper, page 156) — the beam is seen as a perfectly straight thread of light inside the beaker.
Shadows — an object always throws a shadow of its own outline right behind it, exactly where a straight beam would be blocked.
Sunbeams — light entering a dark room through a small window, or through leaves in a misty forest, is seen as straight beams.
Try This: Look at a bulb through a rolled paper tube. Bend the tube even a little and the bulb disappears — one more proof, using nothing but a sheet of paper.