The focal length of a convex lens is 10 cm. On immersing in water, it will act as a :
- AConvex lens of focal length 10 cm
- BConcave lens of focal length 10 cm
- CConvex lens of focal length more than 10 cm
- DMore than one of the above
- ENone of the above
Show answer and explanation
Correct answer: (c) Convex lens of focal length more than 10 cm
Explanation
A lens bends light because its refractive index differs from that of its surroundings. Glass (about 1.5) differs less from water (about 1.33) than from air.
So in water the lens bends light less: it still converges (acts as a convex lens), but its focal length becomes longer than 10 cm (about four times, for ordinary glass).