Optics : Definitions

Front 1

Define, a Lens

Back 1

A Lens is defined as, an optical device made from plastic or glass, which as a result of refraction cause light rays that pass through it, to converge to a point or diverge from a point.

Front 2

Define, a Virtual Image

Back 2

A Virtual image is defined as, an image formed, when all the rays from a point on an object appear to spread out from this single point.

Front 3

Define, a Real Image

Back 3

A Real image is defined as, an image that is formed, when all the rays from a point on an object, are brought together again at another single point.

Front 4

Define, Deviation.

Back 4

Deviation is defined as, a change in the direction, of a ray of light from its normal path, due to an interaction with a medium.

Front 5

Define, Dispersion.

Back 5

Dispersion is defined as, the separation of white light, into its constituent colours on interfacing with a prism, or a optical medium with similar properties.

Front 6

Define, a Mirage.

Back 6

A mirage is defined as, an optical illusion, that occurs due to changes in the refractive index of the air, as a result of changes in air density.

Front 7

Define, Linear magnification.

Back 7

Linear magnification, is defined as, a ratio, of an image's distance or height to an object's distance or height.

Front 8

Define, the Principal axis of a Lens.

Back 8

The principal axis of a Lens, is defined as, the imaginary horizontal line, joining the centres of curvature of the faces of a lens

Front 9

Define, the focal length of a Lens.

Back 9

The focal length of a Lens, is defined as, the distance from the principal focus, to the optical centre of a lens.

Front 10

Define, Reflection.

Back 10

Reflection is defined as, phenomenon which occurs when light rays strikes a polish or shiny plane boundary, all or part of it returns into the medium.

Front 11

Define, Refraction.

Back 11

Refraction is defined as, the bending of light, which occurs when light passes, from one transparent medium to another.

Front 12

Define, the Angle of Incidence

Back 12

The Angle of Incidence, is defined as, the angle between the incident ray and the normal.

Front 13

Define, the Angle of Refraction.

Back 13

The Angle of Refraction, is defined as, the angle between the refracted ray and the normal.

Front 14

Define, the Critical Angle, of a Pair of Media

Back 14

The Critical Angle, of a pair of media is defined as, the angle of incidence in the optically denser medium, for which the angle of refraction is 90°

Front 15

Define, A Ray.

Back 15

A Ray is defined as, the direction of the path in which light travels.

Front 16

Define, A Beam of Light.

Back 16

A Beam of light is defined as, a collection of light rays.

Front 17

Define, A Shadow.

Back 17

A Shadow is defined as, a dark region which is formed, when an opaque object blocks completely or partially, the direct pathway of light rays from a light source.

Front 18

Define, A Point Source.

Back 18

A Point Source of Light.

Hint 18

A Point Source is defined as a source of light which is small enough for all the rays of light to come effectively from a single point from the source.

Front 19

Define, An Extended Source.

Back 19

An Extended Source, is defined as, a source of light which is large enough, for all the rays of light to seem to come effectively, from many points from a source.

Front 20

Define, An Umbra.

Back 20

An Umbra, is defined as, the part of a shadow, that is uniformly and totally dark.

Front 21

Define, A Pen-Umbra.

Back 21

A Penumbra is defined as, the part of a shadow, that is partially dark.

Front 22

Give the 2 light phenomena that Isaac Newtons Corpuscular Theory of light, could not explain.

Back 22

The 2 phenomena are, Interference of Light and Diffraction of Light

Front 23

Give the 2 light phenomena that Christian Huygens Wave Theory of Light, could not explain.

Back 23

The 2 phenomena are, The Reflection of Light and Refraction of Light.

Front 24

Define, A Prism.

Back 24

A Prism is defined as a triangular shaped block of transparent material, that is capable of turning, parallel light rays that incident normally to their faces, through angles of 90° or 180°.

Front 25

Give 2 reasons why, prisms are used in preference to plane mirrors in optical instruments like periscopes and binoculars.

Back 25

Right angled prisms are used in preference to plane mirrors because, 1) prisms do not have exposed silvered surfaces, that can be peeled, scratched or damage. 2) prisms do not give, multiple reflected images, as would thick plane mirrors.

Front 26

Briefly explain, why of all the colours of light in the visible spectrum. red coloured light, experiences the least deviation when white light interface with a prism.

Back 26

Red coloured light undergoes the least deviation because, light of longer wavelength, such as red, is slowed down much less than the others, and so undergoes the least amount of refraction at both surfaces of the prism.

Front 27

Briefly explain, why of all the colours of light in the visible spectrum. violet coloured light, experiences the most deviation when white light interface with a prism.

Back 27

Violet coloured light undergoes the greatest deviation because, light of shorter wavelength, such as violet, is slowed down much more than the others, and so undergoes the greatest amount of refraction at both surfaces of the prism.

Front 28

Give the reason for eyes experiencing Colour.

Back 28

The eyes can detect light of different frequencies. The different frequencies of light is what gives the many colours of the visible spectrum.