Physics Light – Reflection and Refraction

Comprehensive vocabulary flashcards covering the principles of reflection, refraction, spherical mirrors, spherical lenses, and optical formulas based on the physics lecture notes.

Reflection of Light

The phenomenon of bouncing back of light into the same medium on striking the surface of any object.

First law of Reflection

The incident ray, the normal to the surface at the point of incidence and the reflected ray, all lie in the same plane.

Second law of Reflection

The angle of reflection ($r$) is always equal to the angle of incidence ($i$), represented as $\text{∠} i = \text{∠} r$.

Plane Mirror Image

The image is always virtual and erect, of the same size as the object, as far behind the mirror as the object is in front of it, and laterally inverted.

Convex mirrors (Diverging mirrors)

Spherical mirrors in which the reflecting surface is curved outwards.

Concave mirrors (Converging mirrors)

Spherical mirrors in which the reflecting surface is curved inwards.

Centre of curvature ($C$)

The centre of the hollow sphere of glass, of which the spherical mirror is a part.

Radius of curvature ($R$)

The radius of the hollow sphere of glass, of which the spherical mirror is a part.

Pole ($P$)

The centre of the spherical mirror.

Principal axis

A straight line passing through the centre of curvature $C$ and pole $P$ of the spherical mirror.

Principal focus ($F$) of a concave mirror

A point on the principal axis at which the rays of light incident on the mirror, in a direction parallel to the principal axis, actually meet after reflection from the mirror.

Principal focus ($F$) of a convex mirror

A point on the principal axis from which the rays of light incident on the mirror, in a direction parallel to the principal axis, appear to diverge after reflection from the mirror.

Focal length ($f$)

The distance between the pole ($P$) and the principal focus ($F$) of a mirror.

Relation between $R$ and $f$

For spherical mirrors of small aperture, $R = 2f$.

New Cartesian Sign Conventions

All distances are measured from the pole; distances in the direction of incidence are positive; heights above the principal axis are positive.

Mirror Formula

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

Linear Magnification ($m$)

Produced by a spherical mirror or lens, defined as $m = \frac{\text{size of image } (h_2)}{\text{size of object } (h_1)}$. It is negative for real images and positive for virtual images.

Refraction of Light

The phenomenon of change in the path of a beam of light as it passes from one medium to another.

Cause of Refraction

The change in the speed of light as it goes from one medium to another.

Snell’s law

The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media: $\frac{\text{sin}(i)}{\text{sin}(r)} = \text{constant}$, written as ${_1n_2}$.

Absolute refractive index ($n$)

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

Refraction from Rarer to Denser medium

The ray of light bends towards the normal.

Refraction from Denser to Rarer medium

The ray of light bends away from the normal.

Convex lens (Converging lens)

A spherical lens which is thick at the centre and thin at the edges.

Concave lens (Diverging lens)

A spherical lens which is thin at the centre and thick at the edges.

Optical centre ($O$)

The central point of a spherical lens.

Principal focus of a convex lens

A point on its principal axis to which light rays parallel to the principal axis converge after passing through the lens.

Principal focus of a concave lens

A point on its principal axis from which light rays, originally parallel to the principal axis, appear to diverge after passing through the lens.

Lens Formula

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

Power of a lens ($P$)

The reciprocal of the focal length ($f$) of the lens, measured in meters: $P = \frac{1}{f(\text{metre})}$.

Dioptre ($D$)

The S.I. unit of the power of a lens.