Waves. Diffraction

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Recording Notice
This lesson is
being recorded

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King’s Interhigh Logo

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Explore 1: Diffraction and Pulse echo technique
Waves – Diffraction – Week 24

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Objectives
Keywords: de Broglie equation, diffraction, diffraction grating, pulse echo technique

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Starter – Post your answer in the poll.
What is wavelength if there are 400 lines per mm and the angle of the
third order maxima is 14.9°?
Step
Detail
Identify
λ = ? lines = 400/mm θ = 14.9°
n=3
Match
d = 0.001m ÷ 400 = 2.5 × 10-6 m
Formula
nλ = d sin θ
Arrange
λ = d sin θ ÷ 3
Substitute
λ = 2.5 × 10-6 sin (14.9) ÷ 3
Total
λ = 214.3 nm
EXTENSION for Explore 1 and 2: Questions from Week 24 PHY Explore 1 and 2 EXTENSION - Waves
When finished, post your score in the Q and A.
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Starter 2
What is wavelength if there are 300 lines per mm and the angle of the second
order maxima is 23.7°. Send your answer in the Q and A.
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Step
Detail
Identify
λ = ? lines = 300/mm θ = 23.7°
n=2
Match
d = 0.001m ÷ 300 = 3.3 × 10-6 m
Formula
nλ = d sin θ
Arrange
λ = d sin θ ÷ 2
Substitute
λ = 3.3 × 10-6 sin (23.7) ÷ 2
Total
λ = 669.9 nm

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Human Echolocation
Ben Underwood 3.02 min
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Calculation
What return time must Ben be
interpreting? The speed of sound is
146 cm
340 m/s.
• t=d÷s
• t = (2 × 1.46) ÷ 340 ms-1
• t = 8.6 ms
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Dolphin Echolocation
How do dolphins use echolocation to
navigate the deep seas? 4.55 min
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Dolphin Wavelength
What will be the wavelength if
frequency is 130 kHz?
Speed of sound in water = 1482 ms -1
• v = fλ
• λ=v÷f
• λ = 1482 ÷ 130,000
• λ = 1.14 cm
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Plenary: Wordwall (Quiz option)
https://wordwall.net/resource/9424639/diffraction
Post your score in the poll.
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Explore 2: Exam Practice
Waves – Diffraction – Week 24

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Objectives
Keywords: de Broglie equation, diffraction, diffraction grating, pulse echo technique

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Starter
How much bigger than an atom is a
light wave?
A. × 10
B. × 100
C. × 1000
D. × 10,000
E. × 100,000
E
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Animal Perception II
Magnetoperception in Foxes 3.15 min
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Explore Activity
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Q1 Optional Questions & Answers
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Q1
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Q2
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Q2
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Q2
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Q2
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Q3
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Q3
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Q4
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Q4
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Q5
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Q5
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Q5
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Plenary
What does laser stand for?
A. Light Arrest by streamlined
empowerment of resistance
B. Light Attenuation by strong
encasement of radon
C. Light Augmentation by striated
enthrallment of rays
D. Light Amplification by stimulated
emission of radiation
D
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Objectives
Keywords: de Broglie equation, diffraction, diffraction grating, pulse echo technique
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Explore 3: Practical
Waves – Diffraction – Week 24

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Objectives
Keywords: de Broglie equation, diffraction, diffraction grating, pulse echo technique
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Starter
Why measure the lengths of the
triangle and use trigonometry instead
of just using a protractor?
• The uncertainty with a protractor
will be greater.
Trigonometry
sin(θ) = O ÷ H
θ = sin -1 (7.8 ÷ 20.3) = 22.6°
0.05 cm ÷ 7.8 cm 0.6%
0.05 cm ÷ 20.3 cm 0.3%
Total uncert = 0.9 %
Protractor
1° ÷ 22° 4.5% uncert
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7.8 cm
20.3 cm

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Practical Sim
• Pretend you can’t see what
the wavelength is set to.
• Use these distances to work
out the angle.
• And this to work out d, the
distance between lines.
• Use nλ = d sin(θ) to find the
wavelength.
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Sample Results
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CP08: Find Wavelength
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Plenary
What is the relationship between wavelength and angle to a given maxima?
• Greater wavelength means greater angle.
nλ = d sin(θ)
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Objectives
Keywords: de Broglie equation, diffraction, diffraction grating, pulse echo technique
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Explore 4: Exam Practice
Waves – Diffraction – Week 24

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Objectives
Keywords: de Broglie equation, diffraction, diffraction grating, pulse echo technique
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Starter Picture Puzzle
Diff(erential) Fraction
Diffraction
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Q1
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Q1
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Q2
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Q2
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Q3
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Q3
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Q3
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Q4
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Q4
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Q4
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Q4
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Q5
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Q5
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