Refraction of Light and Lenses

This set of vocabulary flashcards covers the fundamental terms and concepts of light refraction, refractive index, and the properties and components of convex and concave lenses as presented in the lecture notes.

Refraction of light

The phenomenon where the direction of propagation of light changes when it travels obliquely from one medium to another of different optical density due to a change in its speed.

Absolute refractive index

The ratio of the speed of light in vacuum or air to the speed of light in a specific medium, expressed as $n = \frac{c}{v}$. For diamond, this value is exactly $2.42$.

Refractive index of air

The value taken as approximately $1.0003$ (or rounded to $1$) because the speed of light in air is only marginally less than that in a vacuum.

Optical density

A measure of how slowly light travels through a medium; a higher optical density corresponds to a higher refractive index and a slower speed of light.

Snell’s law of refraction

The law stating that the ratio of the sine of the angle of incidence ($i$) to the sine of the angle of refraction ($r$) is a constant for light of a given color and a given pair of media.

Lateral displacement

The perpendicular distance between the original path of an incident light ray and the path of the emergent ray after it passes through a transparent rectangular glass slab.

Convex lens

A lens that is thicker at the middle than at the edges, also known as a converging lens because it converges parallel beams of light to a single point.

Concave lens

A lens that is thicker at the edges than at the middle, also known as a diverging lens because it diverges a parallel beam of light.

Optical centre

The central point of a lens through which a ray of light passes without any deviation.

Principal axis

An imaginary straight line passing through the two centres of curvature of a lens.

Principal focus

A point on the principal axis where rays incident parallel to the axis converge (in a convex lens) or appear to diverge from (in a concave lens) after refraction.

Focal length

The distance between the principal focus and the optical centre of a lens.

Aperture

The effective diameter of the circular outline of a spherical lens.

Power of a lens

The ability of a lens to converge or diverge a parallel beam of light, calculated as the reciprocal of the focal length in metres ($P = \frac{1}{f}$).

Dioptre ($D$)

The standard unit of power of a lens, where $1$ dioptre is the power of a lens with a focal length of $1\,m$.

Speed of light in vacuum

The highest possible speed in vacuum, accepted as $3 \times 10^{8}\,m/s$.

Centre of curvature

The centre of the sphere of which the lens surface is a part; each lens has two.

Radius of curvature

The radius of the sphere of which the lens surface is a part, represented by the distance from the optical centre to the centre of curvature.

Refractive index of water

The value of $1.33$, meaning the ratio of the speed of light in air to the speed of light in water is $1.33$.