Embed Size (px)
Citation preview
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)
