Light – Reflection and Refraction

Vocabulary flashcards covering the definitions, principles, formulas, and terminology of reflection, spherical mirrors, refraction, spherical lenses, and lens power.

Diffraction of light

The tendency of light to bend around an opaque obstacle and not travel in a straight line when the obstacle on its path becomes very small.

Quantum theory of light

The modern physical theory in which light is treated as neither purely a 'wave' nor a 'particle', reconciling its particle properties with its wave nature.

Laws of reflection of light

Two physical laws stating that: (1) the angle of incidence is equal to the angle of reflection, and (2) the incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane.

Spherical mirror

A curved mirror whose reflecting surface forms part of the surface of a sphere.

Concave mirror

A spherical mirror whose reflecting surface is curved inwards, facing towards the centre of the sphere.

Convex mirror

A spherical mirror whose reflecting surface is curved outwards.

Pole ($P$)

The centre point of the reflecting surface of a spherical mirror, situated on the mirror surface.

Centre of curvature ($C$)

The centre of the sphere of which the reflecting surface of a spherical mirror forms a part; it lies outside the reflecting surface.

Radius of curvature ($R$)

The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, equal to the distance between the pole and the centre of curvature ($PC$).

Principal axis

An imaginary straight line passing through the pole and the centre of curvature of a spherical mirror, acting normal to the mirror at its pole.

Principal focus of a concave mirror

A specific point on the principal axis where rays of light travelling parallel to the principal axis converge and intersect after reflection.

Principal focus of a convex mirror

A point on the principal axis behind the mirror from which reflected rays appear to diverge when incident rays travel parallel to the principal axis.

Focal length ($f$)

The distance between the pole (or optical centre of a lens) and the principal focus of a spherical optical element.

Aperture

The effective diameter of the circular outline of the reflecting or refracting surface of a spherical mirror or lens.

New Cartesian Sign Convention

The convention where the mirror pole or lens optical centre is the origin, light falls from the left, distances along $+x$ are positive, distances along $-x$ are negative, heights above the principal axis are positive, and heights below are negative.

Mirror formula

The mathematical relationship between object distance ($u$), image distance ($v$), and focal length ($f$) for spherical mirrors: $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$.

Magnification ($m$) of a mirror

The ratio of the height of the image ($h'$) to the height of the object ($h$), which is also equal to $- \frac{v}{u}$.

Refraction of light

The change in direction of propagation of light when it travels obliquely from one transparent medium into another due to a change in the speed of light.

Snell’s law of refraction

The principle stating that for a given pair of media and a given colour of light, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant: $\frac{\sin(i)}{\sin(r)} = \text{constant}$.

Absolute refractive index ($n_m$)

The ratio of the speed of light in vacuum or air ($c$) to the speed of light in the given medium ($v$), given by $n_m = \frac{c}{v}$.

Optical density

A medium's ability to refract light; a medium with a higher refractive index is optically denser, slowing light down and bending it towards the normal, independent of mass density.

Convex lens

A converging lens bound by two spherical surfaces bulging outwards, which is thicker in the middle than at the edges.

Concave lens

A diverging lens bound by two spherical surfaces curved inwards, which is thicker at the edges than at the middle.

Optical centre ($O$)

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

Lens formula

The equation relating object distance ($u$), image distance ($v$), and focal length ($f$) for spherical lenses: $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$.

Magnification ($m$) of a lens

The ratio of the height of the image ($h'$) to the height of the object ($h$), expressed in terms of image and object distances as $m = \frac{h'}{h} = \frac{v}{u}$.

Power of a lens ($P$)

The degree of convergence or divergence of light rays achieved by a lens, defined as the reciprocal of its focal length: $P = \frac{1}{f}$.

Dioptre ($D$)

The SI unit of power of a lens, equivalent to $1\,\text{m}^{-1}$, defined as the power of a lens having a focal length of $1\,\text{m}$.