P4 Light

Note by ShreyaDas, updated more than 1 year ago
Created by ShreyaDas over 6 years ago


IGCSE Physics (P4 Light and the Electromagnetic Spectrum) Note on P4 Light, created by ShreyaDas on 13/03/2014.

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Reflection with Light Waves/Rays The angle of incidence is equal to the angle of reflection!The light ray hits a mirror plane and reflects so that you are able to see an image. The mirror creates a virtual image as the light rays do not pass through the mirror plane. Therefore, these images cannot be put onto a screen.The image in a plane mirror is always: Laterally inversed (i.e. back to front) Has the same distance behind the mirror as the object is in front Same size as the object Same shape and colour  Same way up  However, in a camera, a real image is created as light is able to pass behind the lens and be captured onto a screen.

Radio waves: television and radiomicro waves: satellite TV broadcastinginfrared radiation: remote controls for devices, security alarmsvisible lightultraviolet: fluorescent lights, sunlightx-rays: hospitals and clinicsgamma rays: kill cancer cells

Virtual image: cannot be formed on a screenall mirrors have virtual images

Refraction: change in direction of light when it passes from one material or medium to another


Light is bent towards the normal when it moves from a less dense medium into a more dense mediumLight is bent away from the normal when it moves from a more dense medium into a less dense medium

Bending relates to the change of speed of light as it moves from one medium to anotherLight travels slower in glass than it does in air- bends toward the nomel when it travels from air to glass

Total Internal Reflection TIR only occurs when there is a different density between the media that the light ray is travelling through.e.g. When it travels through glass.It is the process in which the light rays are reflected from the inside edge of the media.Critical Angle:It is the angle which causes the light ray to exit the glass block at 90 degrees to the normal i.e. That there is NO refraction.If an angle of incidence i below the critical angle then TIR does not occur.If an angle of incidence is above the critical angle then TIR does occur.Uses in Optical Fibres: Uses TIR to travel along a solid rod made from glass/plastic The centre core of a Optical fibre is made from a glass with a high reflective index i.e.OPTICALLY DENSE The coating is made of a material less optically dense The light hits the boundary between the two media at an angle greater than the critical angle so that TIR takes place A bundle of Optical Fibres are able to make an endoscope to look inside a body.

Focal point: point where image is at the most focusReal Image: can be formed on a screenVirtual: cannotErect: uprightInverted: upside downDiminished: smaller

Drawing Ray Diagrams:- one ray passing through centre of lens- one parallel to principal acis but is bent when it goes through optical centre (refraction)-- or other way round

Light:- t

Light:- transverse wave- small wavelength- very high speed (3x10^9 m/s)


When white light is refracted through a prsm it splits up into its individual colours- happens because each colour (wavelength) travels at a different speed in the glass prismCALLED DISPERSION 


RED is fastestVIOLET is slowest

Reflection of Light


Total Internal Reflection

Converging Lens

Colour and Dispersion of Light

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