Q1.
Pass a laser beam through a beaker filled with water in which a drop of milk is added to make the laser beam easily visible. What do you observe? Do you see that the beam of laser light inside water follows a straight path?
Answer
Inside the milky water the laser beam is seen as a thin, perfectly straight red line going from one side of the beaker to the other. Yes — the beam follows a straight path in water too.
Why it happens: Plain water is transparent, so a beam passing through it cannot be seen from the side. The tiny fat droplets of milk scatter a little of the light sideways to your eye, and that scattered light traces out the path of the beam. What it traces is a straight line — showing that light travels straight in water just as it does in air.
Caution: Use a low-power laser pointer only, under your teacher's supervision, and never point it at anyone's eyes.
Did you know? Light can be made to bend around corners — inside the thin glass fibres (optical fibres) that carry telephone and internet signals. You will learn how this happens in higher classes.