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Question
Answer the following question.
What is focal power of a spherical mirror or a lens? What may be the reason for using P = `1/"f"` as its expression?
Solution
- Converging or diverging the ability of a lens or of a mirror is defined as its focal power.
- This implies, the more the power of any spherical mirror or a lens, the more is its ability to converge or diverge the light that passes through it.
- In the case of a convex lens or concave mirror, the more the convergence, the shorter is the focal length as shown in the figure.
- Similarly, in the case of a concave lens or convex mirror, the more the divergence, the shorter is the focal length.
- This explains that the focal power of any spherical lens or mirror is inversely proportional to the focal length.
- Hence, the expression of focal power is given by the formula, P = `1/"f"`.
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