Experiment – 2
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
f=\frac{R}{2}
Ray Diagram
Calculation
mean,\;f=\frac{23.3+22.9+23.4}{3}=23.20
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.
