Give scientific reasons:
a. Simple microscope is used for watch repairs.
b. One can sense colours only in bright light.
c. We cannot clearly see an object kept at a distance less than 25 cm from the eye.
Answer:
(a) A simple microscope used in repairing watches has a convex lens of small focal length with magnification capacity up to 20 times. Therefore, it is used by watch repairers to check the smallest parts of the watch clearly and it does not cause any strain on eyes.
(b) We can sense colours only in light because when it gets dark the cones ability to respond to light is lost and the rods continue to respond to available light. However cones cannot see color, everything looks like shades of black and white and gray.
(c) Eyes can see its distant and close objects. It adjusts its focal length by contracting or relaxing ciliary muscles to see the objects. The ciliary muscles cannot be contracted below a certain minimum limit. Therefore we cannot see an object kept at a distance less than 25 cms from the eye.
