Question

In a spherical mirror the distance between its centre of curvature and pole is 20 cm. What is the distance of focus from the pole of the mirror?

• A. 5 cm
• B. 10 cm
• C. 15 cm
• D. 20 cm

Hint:

For all spherical mirrors, the focal length is half of the radius of curvature, i.e., \( f = \frac{R}{2} \).

Answer 1

The Correct Option is B

Step 1: Recall the relationship between radius of curvature and focal length.
For any spherical mirror, the relation is given by: \[ f = \frac{R}{2} \] where \( f \) is the focal length and \( R \) is the radius of curvature.
Step 2: Substitute the given values.
Given that \( R = 20 \, \text{cm} \), we get \[ f = \frac{20}{2} = 10 \, \text{cm} \] Step 3: Conclusion.
Therefore, the focal length of the mirror (distance of focus from the pole) is 10 cm.