This contains about light properties

1. In this unit:
1) Properties of light
2) Reflection
3) Refraction
4) Total Internal Reflection
5) Optical Fibre

2. Part 1 – Properties of Light
Light travels in straight lines:
Laser

3. Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.

4. Light travels much faster than sound. For example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.

5. We see things because they reflect light
into our eyes:
Homework

6. Shadows
Shadows are places where light is “blocked”:
Rays of light

7. Properties of Light summary
1) Light travels in straight lines
2) Light travels much faster than sound
3) We see things because they reflect light into
our eyes
4) Shadows are formed when light is blocked by
an object

8. Reflection of light
The phenomenon of bouncing back of
light in same medium from reflecting
surface.

9. Reflection
Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of
incidence
Angle of
reflection
Mirror
ii r

10. The Law of ReflectionThe Law of Reflection
 Angle of incidence = Angle ofAngle of incidence = Angle of
reflectionreflection
The
same !!!
The incident ray, normal & reflected ray all lie
one plane.
 The incident ray and reflected ray are on
opposite side of normal.
Incident ray Reflected ray
Normal
ii r

11. Refraction
• The change in direction of a wave as is
crosses the boundary between two media
in which the wave travels at different
speeds.

14. Snell’s Law
n
n
n
nn
==
=
1
2
2
1
2211
sin
sin
sinsin
θ
θ
θθ

15. Refractive Index
materialinlightofspeed
vacuuminlightofspeed
n=
It also denoted by µ

16. A
 A prism is a portion of transparent
refracting medium bounded by three
rectangular and triangular faces.
 The angle between the refracting
faces is called angle of prism.

22. The phenomenon of bending of light, when
light strike on boundary separating two media at angle
of incident greater than critical angle is called as total
internal reflection.

23. Critical Angle
Critical angle is defined as that angle of
incidence for which the angle of refraction r is
equal to 90o
.
It is given by
C = sin -1
( )

24. Optical fibre is a transmitting media
just like human hair.

25. Structure of Optical Fibre