Light – Reflection and Refraction

Vocabulary flashcards covering the key terms, laws, formulas, and principles of reflection and refraction from Chapter 9.

Diffraction of light

The phenomenon in which light bends around an opaque object and does not travel in a straight line when the opaque object in its path becomes very small.

Laws of reflection of light

The two fundamental rules of reflection: (1) The angle of incidence is equal to the angle of reflection ($i = r$), and (2) The incident ray, the normal to the mirror at the point of incidence, and the reflected ray, all lie in the same plane.

Spherical mirror

A curved mirror whose reflecting surface is spherical and can be considered to form a 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 point located at the centre of the reflecting surface of a spherical mirror, lying directly 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 (in front of a concave mirror and behind a convex mirror).

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 $PC$.

Principal axis (Spherical mirror)

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

Principal focus of a concave mirror

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

Principal focus of a convex mirror

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

Focal length ($f$)

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

Aperture (Spherical mirror)

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

Relationship between $R$ and $f$

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

New Cartesian Sign Convention

A coordinate system convention where the pole or optical centre is the origin, distances to the right are positive, distances to the left are negative, heights above the principal axis are positive, and heights below the principal axis are negative.

Mirror formula

The relation connecting object distance ($u$), image distance ($v$), and focal length ($f$) of a spherical mirror: $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$.

Magnification ($m$) of a spherical mirror

The ratio of the height of the image ($h'$) to the height of the object ($h$), which is also equal to $-\frac{v}{u}$; a negative sign denotes a real image, while a positive sign denotes a virtual image.

Refraction of light

The change in the direction of propagation of light when it passes obliquely from one transparent medium into another, resulting from 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 a given colour of light and pair of media: $\frac{\sin(i)}{\sin(r)} = \text{constant}$.

Refractive index ($n_{21}$)

The ratio of the speed of light in medium 1 ($v_1$) to the speed of light in medium 2 ($v_2$), defined 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, defined as $n_m = \frac{c}{v}$, where $c = 3 \times 10^8\,\text{m/s}$ is the speed of light in vacuum and $v$ is the speed of light in the medium.

Optical density

The ability of a medium to refract light; an optically denser medium has a higher refractive index and slower light speed than an optically rarer medium.

Convex lens

A converging lens bounded by two spherical surfaces bulging outwards that is thicker in the middle than at the edges.

Concave lens

A diverging lens bounded by two spherical surfaces curved inwards that is thicker at the edges than at the middle.

Optical centre ($O$)

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

Principal axis (Lens)

An imaginary straight line passing through the two centres of curvature ($C_1$ and $C_2$) of a lens.

Principal focus of a convex lens

The point on the principal axis to which rays of light parallel to the principal axis converge after refracting through a convex lens.

Principal focus of a concave lens

The point on the principal axis from which rays of light parallel to the principal axis appear to diverge after refracting through a concave lens.

Lens formula

The relation connecting object distance ($u$), image distance ($v$), and focal length ($f$) of a spherical lens: $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$.

Magnification ($m$) of a lens

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

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 in metres ($P = \frac{1}{f}$).

Dioptre ($\text{D}$)

The SI unit of power of a lens, where $1\,\text{D} = 1\,\text{m}^{-1}$, representing the power of a lens with a focal length of $1\,\text{m}$.