last lesson light travels faster than sound using ray boxes the law of reflection
TRANSCRIPT
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Last lesson
• Light travels faster than sound
• Using ray boxes
• The law of reflection
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Reflection
Incident ray
Normal
Reflected ray
Angle of incidence
Angle of reflection
Mirror
Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection
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Mirror Island
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Today’s lesson
• Refraction of light
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The mug trick!
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An InvestigationWhat does water do to the
path of light? Can we explain the “Mug Trick’?
“Mirror Island II” due in Monday 25th!
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Gather round!
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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
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Refraction of light
Glass block
Beam of light
Glass block
Beam of light
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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?
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Refraction
When a wave changes speed (normally when entering another medium) it may refract (change direction)
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Water waves
Water waves travel slower in shallow water
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Light waves
Light slows down as it goes from air to glass/water
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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
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Snell’s law
i
r
Ray, NOT wavefronts
speed in substance 1 = sin(i)speed in substance 2 sin(r)
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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)
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Refraction – a few notes
The wavelength changes, the speed changes, but the frequency stays the same
Ripple Tank Simulation
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Let’s try some questions!Page 147 Questions
1, 2 and 3.
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Measuring refractive index
i
r
Ray, NOT wavefronts
refractive index (η) = sin(i)
sin(r)