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Core Physics – Energy
L/O :- To understand diffraction
Diffraction
Exam Date -
Quick Quiz - What do you remember from last lesson?
• Draw and label a wave• What is the law of reflection?• What is the equation for working out the
speed of a wave?• What happens to a light ray when it
travels from air through glass? Why does this happen?
• What is the equations for working out efficiency?
• What are the 2 different types of wave? Give an example
• How do you work out the pay-back time for insulation?
• What are the pros and cons of wind energy?
• Where are step-up transformers used?• How does increasing the volume of a
sound affect the wave?
What is happening in this picture?
If sound and light are both waves. why
can you hear around a
corner but not see round it?
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Wave behaviour1) Reflection
4) Diffraction3) Refraction
2) Refraction
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DiffractionMore diffraction if the size of the gap is similar to the
wavelength
More diffraction if wavelength is increased (or frequency decreased)
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Sound can also be diffracted…
The explosion can’t be seen over the hill, but it can be heard. We know sound travels as waves
because sound can be refracted, reflected (echo) and diffracted.
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Diffraction depends on frequency…
A high frequency (short wavelength) wave doesn’t get diffracted much – the house won’t be able to receive
it…
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Diffraction depends on frequency…
A low frequency (long wavelength) wave will get diffracted more, so the
house can receive it…
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InterferenceInterference is seen when two waves of the same type cross:
Interference
When 2 waves meet, they interfere with each other.
If they meet each other exactly in phase, the amplitudes ‘add up’ to produce large crests and troughs.
+ =
This is called constructive interference.
If they meet each other exactly out of phase, the amplitudes ‘subtract’ to produce no peaks or crests.
+ =
This is called destructive interference.
Interference
20/04/23
Interference Patterns from 2 slits
Intensity
Distance
Constructive interference
Destructive interference
How could you test your
prediction?What will you
record?
Design a table
What type of graph should you use to represent your
data?
How could you check the
reproducibility
Can you work out the refractive index?
Refractive index = sin i sin r
What have you learnt?
• Do you know what diffraction is?• Can you predict how these waves would behave?
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