Light presentation

In this unit:

1) Properties of light2) Reflection3) Refraction4) Total Internal Reflection5) Optical Fibre

Part 1 – Properties of Light

Light travels in straight lines:

Laser

Light travels VERY FAST – around 300,000 kilometres per second.

At this speed it can go around the world 8 times in one second.

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.

We see things because they reflect light into our eyes:

Homework

Shadows

Shadows are places where light is “blocked”:

Rays of light

Properties of Light summary

1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect light into

our eyes4) Shadows are formed when light is blocked by

an object

Reflection of Light

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

ReflectionReflection from a mirror:

Incident ray

NormalReflected ray

Angle of incidence

Angle of reflection

Mirror

ii r

The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle 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

Refraction• The change in direction of a wave as is

crosses the boundary between two media in which the wave travels at different speeds.

Snell’s Law

nnnnn

1

2

2

1

2211

sinsin

sinsin

Refractive Index

materialinlightofspeedvacuuminlightofspeedn

It also denoted by µ

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.

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.

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 ( )

Optical fibre is a transmitting media just like human hair.

Structure of Optical Fibre