To find the value of v for different values of u in the case of a concave mirror and to find the focal length | cbse class 12th physics practical

Objective

To find the value of v for different values of u in case of a concave mirror and to find the focal length.

Apparatus Required

A knitting needle, a half metre scale, an opticle bench with three uprights, two needles and concave mirror with mirror holder.

Formula Used

Ray Diagram

Observations

Calculation

Result

Mean value of focal length, f = 15.0 cm

(as per sign convention the focal length of concave mirror is negative) =- 15.0 cm

Focal length of concave mirror = 15 cm

Precaution

• Tip to tip parallax should be removed between needle and the image of the object needle.
• Index correction for u and u should be properly determined and must be applied.
• All the uprights should be vertical and principal axis of the mirror should be horizontal.
• To locate the position of the image, the eye should be at least 30 cm away from the needle.
• Tips of the needles and the pole of the mirror should be at the same height as that of the pole of the mirror.

Sources of Errors

• The parallax removal may not be perfect.
• The uprights may not be vertical.