Power of Lens

Rarely Tested

Power of Lens

### Formula

$$P=\frac1f$$

### Terminologies

- P → Power of lens.

- f → Focal length in metre.

### SI Unit

$$Dioptre(D)$$

### Conditions / Special Cases

For convex lens:

$$P>0$$

For concave lens:

$$P<0$$

### Usage

- Used in lens power calculations.

Question 1

A double convex lens made of glass of refractive index $$1.5$$ and radii of curvature of the curved surfaces $$20\,\mathrm{cm}$$ each is immersed in a liquid of refractive index $$n_L$$. The correct plot showing the variation of the power, in the units of diopter ($$D$$), as a function of $$n_L$$ is:

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