Last lesson

• Light travels faster than sound

• Using ray boxes

• The law of reflection

Reflection

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

Mirror Island

Today’s lesson

• Refraction of light

The mug trick!

An InvestigationWhat does water do to the

path of light? Can we explain the “Mug Trick’?

“Mirror Island II” due in Monday 25th!

Gather round!

Mug Investigation

• You are going to pass light through the blocks without water and with water

• Draw around the block and pass light through (at a point and angle of your choice)

• Trace the path of the beam.

• Keeping everything in the same position, pour water in and record where the beam goes.

• Repeat for 2 different positions/angles

• Join the lines to show what happens INSIDE the block.

Title

Refraction of light

Glass block

Beam of light

Glass block

Beam of light

Refraction

Glass block

Beam of lightLight going from air to glass bends towards the normal

Light going from glass to air bends away the normal

Can you copy this please?

Refraction

When a wave changes speed (normally when entering another medium) it may refract (change direction)

Water waves

Water waves travel slower in shallow water

Light waves

Light slows down as it goes from air to glass/water

Snell’s law

There is a relationship between the speed of the wave in the two media and the angles of incidence and refraction

i

r

Ray, NOT wavefronts

Snell’s law

i

r

Ray, NOT wavefronts

speed in substance 1 = sin(i)speed in substance 2 sin(r)

Snell’s law

i

r

Ray, NOT wavefronts

In the case of light only, this quantity is called the refractive index (η)

η = sin(i)

sin(r)

Refraction – a few notes

The wavelength changes, the speed changes, but the frequency stays the same

Ripple Tank Simulation

Let’s try some questions!Page 147 Questions

1, 2 and 3.

Measuring refractive index

i

r

Ray, NOT wavefronts

refractive index (η) = sin(i)

sin(r)