Refraction

Refraction

RefractionRefractionAlthough light

travels in straight lines, it bends when it passes from one medium to another

Although light travels in straight lines, it bends when it passes from one medium to another

Medium (plural “media”) - the material that is being used or undergoing a process

RefractionRefraction

Refraction = the bending of light rays as they pass between two different media

Refraction = the bending of light rays as they pass between two different media

RefractionRefraction

Refraction occurs due to changes in the speed of light in different mediums

Different media slow down light by different amounts

The more that light slows down, the more the light is refracted

Refraction occurs due to changes in the speed of light in different mediums

Different media slow down light by different amounts

The more that light slows down, the more the light is refracted

Refraction in WaterRefraction in Water

• Light rays change direction at the surface of the water

• The image of the chest appears to be more shallow than the actual chest

Speed of LightSpeed of LightIn a vacuum:

However, it is impossible for light to move at this speed when particles get in the way…

In a vacuum:

However, it is impossible for light to move at this speed when particles get in the way…

or

RefractionRefraction The particles in a medium slow down

the passage of light waves Light only refracts at the boundary

when it is entering or leaving a medium

The particles in a medium slow down the passage of light waves

Light only refracts at the boundary when it is entering or leaving a medium

Index of RefractionIndex of Refraction

Index of Refraction = the amount by which a transparent medium decreases the speed of light

Index of Refraction = the amount by which a transparent medium decreases the speed of light

or

(since units cancel, a refractive index does not have any units)

Given:Speed of light in glass = 1.91 x 108 m/sSpeed of light in vacuum = 3.00 x 108 m/s

= 1.57= 3.00 x 108 m/s 1.91 x 108 m/s

The refractive index is 1.57

Given:Refractive index in water = 1.33Speed of light in a vacuum = 3.00 x 108 m/s

v = 2.26 x 108 m/s

1.33 = 3.00 x 108 m/s

v

The speed of light in water is 2.26 x 108 m/s

How Light RefractsHow Light RefractsThe part of the light beam that hits

the medium first will slow down first

The part of the light beam that hits the medium first will slow down first

Angle of RefractionAngle of Refraction

low refractive index (e.g. air) high refractive index (e.g. glass)

Light bends towards the normal

low refractive index (e.g. air) high refractive index (e.g. glass)

Light bends towards the normal

The angle of refraction is measured relative to the normal

The angle of refraction is measured relative to the normal

Angle of RefractionAngle of Refraction

high refractive index (e.g. glass) low refractive index (e.g. air)

Light bends away from the normal

high refractive index (e.g. glass) low refractive index (e.g. air)

Light bends away from the normal

DispersionDispersion

The amount of refraction is different for each colour

A single beam of white light can be split into a rainbow of colours

Dispersion = the refraction of white light into separate wavelengths (colours)

The amount of refraction is different for each colour

A single beam of white light can be split into a rainbow of colours

Dispersion = the refraction of white light into separate wavelengths (colours)

RainbowsRainbows

RainbowsRainbows