Power of a Lens in Physics

Power of a Lens

Definition

• The power of a lens is a measure of its ability to converge or diverge light rays.
• It is defined as the reciprocal of the focal length of the lens.

Units

• The unit of power of a lens is dioptre (D).
• 1 dioptre is equivalent to a focal length of 1 metre.

Formula

• The power of a lens (P) can be calculated using the formula:

P = 1 / f

where f is the focal length of the lens in metres.

Sign Convention

• A converging lens (convex lens) has a positive power.
• A diverging lens (concave lens) has a negative power.

Lens Combinations

• When two or more lenses are combined, their powers add algebraically.
• The total power of the combination is the sum of the individual powers.

Example

• A convex lens has a power of +2D and a concave lens has a power of -3D. The total power of the combination is:

P_total = +2D - 3D = -1D

The combination behaves like a diverging lens.

Power of a Lens

• The power of a lens measures its ability to converge or diverge light rays.
• It is defined as the reciprocal of the focal length of the lens.

Units

• The unit of power of a lens is dioptre (D).
• 1 dioptre is equivalent to a focal length of 1 metre.

Formula

• The power of a lens (P) is calculated using the formula: P = 1 / f, where f is the focal length of the lens in metres.

Sign Convention

• Converging lenses (convex lenses) have positive power.
• Diverging lenses (concave lenses) have negative power.

Lens Combinations

• When combining two or more lenses, their powers add algebraically.
• The total power of the combination is the sum of the individual powers.
• The total power determines the behaviour of the combination, whether converging or diverging.

Example of Lens Combination

• A convex lens with a power of +2D combined with a concave lens with a power of -3D has a total power of -1D.
• The combination behaves like a diverging lens.