Physics Standard - X: Lenses

Vocabulary flashcards covering the fundamental concepts, definitions, and equations related to lenses as presented in the Physics Standard X curriculum.

Lens

A transparent medium in which each refracting surface is part of the spheres.

Convex lens

A lens that is thicker in the middle and has the ability to converge light rays.

Concave lens

A lens that is thinner in the middle (thicker at the edges) and diverges light rays.

Optic centre ($O$)

The midpoint of a lens.

Centres of curvature ($C_1, C_2$)

The centres of the spheres of which each refracting surface of a lens is a part.

Optic axis

The imaginary line passing through the centres of curvature and the optic centre of a lens.

Aperture

The area of the lens through which light passes.

Principal focus of a convex lens ($F$)

The point on the optic axis where light rays near and parallel to the optic axis converge after refraction.

Principal focus of a concave lens ($F$)

The point on the optic axis from which light rays near and parallel to the optic axis appear to diverge after refraction.

Focal length ($f$)

The distance from the optic centre of the lens to the principal focus.

Real image

An image that can be projected or captured on a screen.

Virtual image

An image that cannot be captured on a screen but can only be seen.

Lens Equation

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$ where $f$ is focal length, $u$ is distance to the object, and $v$ is distance to the image.

Magnification ($m$)

The ratio of the height of the image ($h_i$) to the height of the object ($h_o$), or the ratio of distance to the image ($v$) to distance to the object ($u$).

Power of Lens ($P$)

The reciprocal of focal length ($P = \frac{1}{f}$) representing the ability of a lens to converge or diverge light rays.

Dioptre ($D$)

The SI unit of power of a lens, equivalent to the power of a lens with a focal length of one metre ($1\,D$).

Objective

In optical instruments like microscopes or telescopes, the lens placed close to the object to be observed.

Eyepiece

The lens through which the image formed by the objective lens is observed.