LIGHT REFLECTION
LIGHT REFRACTION
SKETCH
FIG 1
FIG 2
Incident angle is between the normal and
the incident ray
Incident angle ≠ refracted angle
i≠r
Incident angle is between the normal and
the incident ray
reflected angle is between the normal and
the reflected ray
refracted angle is between the normal and
the refracted ray
Incident angle = reflected angle
ANGLES
i=r
Reflection is the bouncing back of light
DEFINITION when it hit a smooth surface
NORMAL
MEDIUM
When light goes through 90o
(perpendicular to the surface) does not
bend
Light goes through the same medium –
incident ray and reflected ray both goes
through air.
Refraction is the bending of light when it
goes from one medium to another because it
change speed and direction
When light goes through 90o (perpendicular
to the surface) does not bend
When it goes from less dense to more
dense eg. air to water it bends towards the
normal (go slower) FIG 1
When it goes from more dense to less dense
eg. water to air it bends away from the
normal (go faster)
FIG 2
Light goes through different medium e.g.
air and glass – incident ray goes through air
refracted ray goes through glass.
REFRACTIVE INDEX
(n) is the quantity how much light gets refracted / how much light is
slowed down/the ratio of the speed of light in a vacuum to the speed of light in a medium
Light travel at a speed of 3 x 108 m/s in a vacuum therefore the refractive index of a vacuum is 1.
n =
𝑺𝑷𝑬𝑬𝑫 𝑶𝑭 𝑳𝑰𝑮𝑯𝑻 𝑰𝑵 𝑽𝑨𝑪𝑼𝑼𝑴
𝑺𝑷𝑬𝑬𝑫 𝑶𝑭 𝑳𝑰𝑮𝑯𝑻 𝑰𝑵 𝑨 𝑴𝑬𝑫𝑰𝑼𝑴
n =
𝒄
c = 3 x 108 m/s
𝒗
In different medium light travels at different speed. In water it travels at 2,3 x 108 m/s
SNELL’S LAW – relates the size of the angle of refraction r to the angle of incidence i
The greater the refractive index the more a ray is bent
Snell’s law in equation form
sin 𝑖
n = sin 𝑟
ni sin θi
=
nr sin θr
DEFINITION




A wave is a disturbance in a medium that moves through matter or space.
Waves carry energy from one place to another NOT matter
Transparent – An object that is clear and light can travel through it e.g. window
Translucent – An object that allows parts of light to travel through it also described
as cloudy
 Opaque – An object that light cannot travel through e.g. clothes, desk, wall
 The speed of light is 3x108m/s or 300 000 km/s
Waves can reflect (bounce off a surface), refract (change direction), or diffract
(bend around an obstacle).
Regular Reflection: Smooth, shiny surfaces have a regular reflection e.g mirror
Diffuse Reflection: is when light is scattered in different directions e.g Rough,
dull surfaces
NORMAL – an imaginary line that makes an angle of 90o with the ray that
touches the surface.
• Refraction: The greater the change in speed of the waves, the more the
waves will bend.
EXERCISE
1
Calculate the speed of light in diamond if diamond’s refractive index is 2,42?
(3)
2
Using the information given in the diagram, calculate the refractive index of medium B
(4)
3
Using the information given in the diagram, calculate the angle of refraction.
(4)
4
A ray of light is travelling through glass (n = 1.60) towards water (n = 1,33) at an angle of
incidence of 25o.
(a)
Use Snell’s law to calculate the angle of refraction.
(b)
Draw a ray diagram showing the angle of incidence and angle of refraction and the normal. (5)
(4)
5
(10)
EXERCISE ANSWERS
1
2
n =
𝒄
𝒗
2,42
=
3𝑋108
𝑣
1,24 X108
3
ni sin θi
=
nr sin θr
1,5 sin 30 = 2,42 sin θr
4
5
θr = 18,1