Science Light – Reflection and Refraction

A comprehensive set of vocabulary flashcards covering the fundamental concepts, definitions, and formulas of light reflection and refraction as presented in the lecture notes.

Diffraction of light

An effect where light has a tendency to bend around a very small opaque object on its path instead of walking in a straight line, necessitating the wave theory of light for explanation.

Modern quantum theory of light

A theory in which light is considered neither a ‘wave’ nor a ‘particle’, reconciling the particle properties of light with its wave nature.

Laws of reflection

Rules stating that (i) the angle of incidence is equal to the angle of reflection, and (ii) the incident ray, the normal to the mirror at the point of incidence, and the reflected ray all lie in the same plane.

Concave mirror

A spherical mirror whose reflecting surface is curved inwards and faces towards the centre of the sphere.

Convex mirror

A spherical mirror whose reflecting surface is curved outwards.

Pole

The centre of the reflecting surface of a spherical mirror, usually represented by the letter $P$.

Centre of curvature

The centre of the sphere of which the reflecting surface of a spherical mirror forms a part, represented by the letter $C$.

Radius of curvature

The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, represented by the letter $R$.

Principal axis

An imaginary straight line passing through the pole and the centre of curvature of a spherical mirror.

Principal focus $(F)$

The point on the principal axis where rays parallel to the principal axis meet (in a concave mirror) or appear to diverge from (in a convex mirror) after reflection.

Focal length $(f)$

The distance between the pole and the principal focus of a spherical mirror.

Aperture

The diameter of the reflecting surface of a spherical mirror, represented as the distance $MN$ in diagrams.

Relationship between $R$ and $f$

For spherical mirrors of small apertures, the radius of curvature is equal to twice the focal length, expressed as $R = 2f$.

New Cartesian Sign Convention

A set of rules for spherical mirrors where the pole $P$ is the origin, the principal axis is the $x$-axis, and distances are measured positive to the right and negative to the left.

Mirror formula

The relationship between object distance $(u)$, image distance $(v)$, and focal length $(f)$ expressed as $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$.

Magnification $(m)$

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

Refraction of light

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

Snell’s law of refraction

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

Refractive index $(n_{21})$

The ratio of the speed of light in medium 1 $(v_1)$ to the speed of light in medium 2 $(v_2)$, expressed as $n_{21} = \frac{v_1}{v_2}$.

Absolute refractive index $(n_m)$

The refractive index of a medium with respect to vacuum or air, calculated as $n_m = \frac{c}{v}$, where $c$ is the speed of light in air ($3 \times 10^8\text{m s}^{-1}$).

Optical density

The ability of a medium to refract light; the medium with the larger refractive index is optically denser, and the one with the lower index is optically rarer.

Convex lens

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

Concave lens

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

Optical centre $(O)$

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

Lens Formula

The relationship between object distance $(u)$, image distance $(v)$, and focal length $(f)$ for a lens, expressed as $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$.

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 expressed as $P = \frac{1}{f}$.

Dioptre $(D)$

The SI unit of power of a lens; $1\text{ dioptre}$ is the power of a lens whose focal length is $1\text{ metre}$ ($1D = 1\text{m}^{-1}$).