Question

Describe an activity to determine principal focus and approdimat focal length of a concave mirror

Answer 1

Focal Length Of A Concave Mirror

Aim: To observe the focal length of a concave mirror.

Materials:

· Concave Mirror

· Retort Stand

· 2 Pins in stands

· Candle

· Matches

· Ruler

· Screen

Procedure:

1. An approximate focal length was found using parallel light from a
distant object.

2. The mirror was placed in a stand. Pin (A) was moved in its stand,
in front of the mirror till there was no parallax between the pin and
its inverted image.

3. The distance from the object to the mirror was measured.

4. The object pin was placed between F and C. Then the second pin (B)
was moved about till there was no parallax between (B) and the image
(A). The distances of the image and objects were measured.

Answer 2

The distance between the pole P of the concave mirror and the focus F is the focal length of the concave mirror. Thus, the focal length of a concave mirror can be estimated by obtaining a 'Real image' of a distant object at its focus, as shown in the figure.