Science Light – Reflection and Refraction

Comprehensive vocabulary flashcards covering the key terms, laws, and formulas of light reflection and refraction from the provided lecture transcript.

Ray of light

The straight-line path of light indicated as a line, suggesting that light travels in straight lines.

Diffraction of light

The tendency of light to bend around a very small opaque object on its path and not walk in a straight line.

Modern quantum theory of light

A theory emerging in the 20th century that reconciles the particle properties of light with the wave nature, treating light as neither solely a 'wave' nor a 'particle'.

Laws of reflection of light

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

Laterally inverted

A characteristic of an image formed by a plane mirror where the left and right sides are reversed.

Spherical mirrors

Mirrors whose reflecting surfaces are spherical, forming part of the surface of a sphere.

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 (P)

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

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; the distance $PC$ is equal to this value.

Principal axis

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

Principal focus (F) of a concave mirror

The point on the principal axis where rays of light parallel to the principal axis meet/intersect after reflection.

Principal focus (F) of a convex mirror

The point on the principal axis from which rays of light parallel to the principal axis appear to diverge after reflection.

Focal length (f)

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

Aperture

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

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 convention where the pole ($P$) is the origin, the principal axis is the x-axis, and light is assumed to fall from the left; distances to the right are positive, left are negative, above axis are positive, and below axis are negative.

Mirror Formula

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

Magnification (m)

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

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 second law of refraction stating that for a given pair of media, the ratio $\frac{\sin(i)}{\sin(r)} = \text{constant}$, where $i$ is the angle of incidence and $r$ is the angle of refraction.

Absolute refractive index ($n_m$)

The ratio of the speed of light in air ($c$) to the speed of light in a medium ($v$), expressed as $n_m = \frac{c}{v}$. Speed of light in vacuum is approx $3 \times 10^8\,m\,s^{-1}$.

Optically denser medium

In comparing two media, the one with the larger refractive index where light travels slower and bends towards the normal.

Optically rarer medium

In comparing two media, the one with the lower refractive index where light travels faster and bends away from the normal.

Double convex lens

A lens bound by two spherical surfaces bulging outwards, thicker in the middle than at the edges; also known as a converging lens.

Double concave lens

A lens bound by two spherical surfaces curved inwards, thicker at the edges than in the middle; also known as a diverging lens.

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 given by $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$.

Power of a lens (P)

Defined as the reciprocal of the focal length ($f$) in metres, expressed as $P = \frac{1}{f}$, representing the degree of convergence or divergence.

Dioptre (D)

The SI unit of power of a lens, where $1\,D = 1\,m^{-1}$; concave lenses have negative power and convex lenses have positive power.