To find the focal length of a convex mirror using a convex lens | cbse class 12th physics practical

Objective

To find the focal length of convex mirror using a convex lens.

Material Required

An optical bench with four upright, a knitting needle, a half-meter scale, a convex lens, a convex mirror, a half-meter scale and a mirror holder.

Formula Used

Ray Diagram

Calculation

Result

The focal length of the convex mirror = 23.20

Precautions

• The tips of the needles and the centres of the lens and the mirror should be at the same height.
• The parallax should be removed from tip to tip.
• The distance between the lens and the mirror should be small.
• While adjusting the image needle, the lens and the object needle should not be disturbed.
• The index correction should be carefully recorded and applied.

Sources of Errors

• Parallax was not removed completely.
• The uprights are not perfectly vertical.
• Optical centre, pole of the mirror and the tip of the object needle are not placed in a line.