Question

The focal length of the concave mirror in the experimental set up, shown alongside, equals:



(1) 10.3 cm
(2) 11.0 cm
(3) 11.7 cm
(4) 12.2 cm

Answer 1

1. A concave mirror converges the rays coming from infinity on its focus and the distance of the focal point from the pole of the mirror is called the focal length.
   
2. In the given figure, the rays are converging at a distance of 4.2 cm and the pole of the mirror is at 15.2 cm.
3. That's why the focal length of the given concave mirror = 15.2 cm - 4.2 cm = 11.0 cm
   Hence, the correct option is (2)