Physics Lesson 6 of 6 — Waves

Waves in Context & Reflection/Refraction

Spec 3.7 · 3.9

Learning Objectives:

3.7 – Use v = f × λ in different contexts including sound waves and electromagnetic waves.
3.9 – Explain that all waves can be reflected and refracted.

Navigation: Arrow Keys or Spacebar

🖨️ Pupil Packs

⏱️ 40-Minute Pacing Guide

Core path (40 min): Arrival → Starter → I Do 1 → We Do 1 → I Do 2 → We Do 2 → Independent → Exit Ticket

FLEX slides (I Do 3 + We Do 3): Use if time allows, or as next-lesson warm-up. Marked with 🟠 FLEX badge.

⏱️ 4 min

Arrival Task

Arrival Task – Recall from Lesson 5

Instructions: Answer from memory. Q1–3 recall v = fλ from L5.

1. 🟢

Write the wave speed equation.

v = f × λ

2. 🟢

f = 5 Hz, λ = 3 m. Calculate v.

v = 5 × 3 = 15 m/s

3. 🟢

What unit is wave speed measured in?

Metres per second (m/s).

4. Lead-in 🪞

When you look in a mirror, you see yourself. When you put a straw in a glass of water, it looks bent. What do you think is happening to the light?

Mirror: the light is bouncing back (reflecting). Straw: the light is bending as it enters the water (refracting).

1. 🟠

v = 330 m/s, f = 110 Hz. Calculate λ.

λ = v ÷ f = 330 ÷ 110 = 3 m.

2. 🟠

State the speed of all EM waves in free space.

3 × 10⁸ m/s (speed of light).

3. 🟠

A radio wave has λ = 1500 m and v = 3 × 10⁸ m/s. Calculate f.

f = v ÷ λ = 3×10⁸ ÷ 1500 = 200,000 Hz.

4. Lead-in 🪞

An echo is a sound wave bouncing off a wall. A swimming pool looks shallower than it really is because light bends. Name these two wave behaviours.

Bouncing = reflection. Bending = refraction.

1. 🔵

A wave has T = 0.04 s and λ = 2 m. Find v.

f = 1/T = 1/0.04 = 25 Hz. v = fλ = 25 × 2 = 50 m/s.

2. 🔵

Explain why increasing f while keeping v constant decreases λ.

v = fλ. If v is constant and f↑, then λ must ↓ to keep the product equal to v. They are inversely proportional at constant speed.

3. 🔵

Sound travels at 330 m/s in air but 1500 m/s in water. A 500 Hz note has different wavelengths in each medium. Explain why.

λ = v/f. Same f but different v → different λ. In water: λ = 1500/500 = 3 m. In air: λ = 330/500 = 0.66 m. Faster speed = longer wavelength.

4. Lead-in 🪞

When light slows down as it enters glass, it changes direction. Using v = fλ, explain what happens to the wavelength (frequency stays constant).

If v decreases and f stays the same, then λ = v/f must decrease. The wavelength gets shorter inside the glass.

⏱️ 3 min

Starter

Starter: Speed Check — Which Type of Wave?

Instructions: For each row, calculate v = f × λ. Then decide: is it a sound wave (~330 m/s) or an EM wave (~3 × 10⁸ m/s)? 4 minutes.

📝 Calculate v, then classify:

f	λ	v = f × λ	Sound or EM?
440 Hz	0.75 m
1 × 10⁶ Hz	300 m
256 Hz	1.29 m
5 × 10¹⁴ Hz	6 × 10⁻⁷ m

💡 Key Speeds

🔊 Sound in air ≈ 330 m/s

💡 All EM waves = 3 × 10⁸ m/s

💡 Hint: If your answer is close to 330 → sound wave. If it's huge (hundreds of millions) → electromagnetic wave.

💡 Did You Know?

Diamonds sparkle because of total internal reflection — light enters the diamond, bounces around inside, and exits in bursts of colour. The diamond cutter's entire job is getting the angles right so refraction and reflection work perfectly.

🧠 Quick Recall (from L5)

A wave has f = 5 Hz and λ = 4 m. What is v?

Try it in your head before we start. Answer: v = f × λ = 5 × 4 = 20 m/s

⏱️ 4 min

I Do

I Do: Using v = fλ in Different Contexts (3.7)

Key Idea: The same equation works for ALL waves — but the speed depends on the wave type and medium.

🔊 Sound Wave Context

Speed of sound in air ≈ 330 m/s (always given or you use this value)

Speed of sound in water ≈ 1500 m/s (faster because water is denser)

Example: Tuning fork at 440 Hz in air:
λ = v ÷ f = 330 ÷ 440 = 0.75 m

Same note in water:
λ = 1500 ÷ 440 = 3.41 m (longer because faster speed!)

🌍 Why This Matters

Without reflection, you'd have no mirrors, no radar, and no ultrasound scans. Without refraction, you'd have no glasses, no cameras, no fibre optic internet, and no rainbows. These two behaviours shape the technology you use every single day.

💡 Key rule: When a wave enters a different medium, speed changes, wavelength changes, but frequency stays the same.

💡 EM Wave Context

All EM waves travel at 3 × 10⁸ m/s in free space (vacuum).

This includes radio, microwave, infrared, visible light, UV, X-ray, gamma.

Example: Radio wave f = 200,000 Hz:
λ = v ÷ f = 3×10⁸ ÷ 200,000 = 1500 m

Example: Green light λ = 5 × 10⁻⁷ m:
f = v ÷ λ = 3×10⁸ ÷ 5×10⁻⁷ = 6 × 10¹⁴ Hz

🌟 Why does sound travel faster in water? Sound needs particles to vibrate through. Water molecules are closer together than air molecules, so vibrations pass between them faster.

🔑 Keywords to Know

Reflection	Wave BOUNCES back off a surface.
Refraction	Wave CHANGES DIRECTION because its speed changes.
Normal	An imaginary line at 90° to the surface.
Medium	The substance the wave travels through (air, water, glass).

⏱️ 5 min

We Do

We Do: Sound or EM? Speed Detective 🔍

Instructions: Each wave has f and λ given. First calculate v mentally, then classify as Sound (~330) or EM (~3×10⁸). Click your answer!

👥 Think-Pair-Share: Try it yourself → discuss with your partner → agree on the answer.

🎻

f = 660 Hz, λ = 0.5 m

v = 660 × 0.5 = 330 m/s

📻

f = 1×10⁶ Hz, λ = 300 m

v = 1×10⁶ × 300 = 3×10⁸ m/s

🎤

f = 1000 Hz, λ = 0.33 m

v = 1000 × 0.33 = 330 m/s

📶

f = 2.4×10⁹ Hz, λ = 0.125 m

v = 2.4×10⁹ × 0.125 = 3×10⁸ m/s

🦇

f = 50,000 Hz, λ = 0.0066 m

v = 50000 × 0.0066 = 330 m/s

Correct: 0 / 5

⏱️ 4 min

I Do

I Do: All Waves Can Be Reflected & Refracted (3.9)

Key Fact: All waves — light, sound, water, EM — can be reflected and refracted.

🪞 Reflection

Reflection = a wave bounces back when it hits a surface.

The angle of incidence = angle of reflection (both measured from the normal).

Examples: Mirror (light), echo (sound), sonar ping off seabed (sound), radar (EM).

Reflection Diagram

🌊 Refraction

Refraction = a wave changes direction when it enters a different medium because its speed changes.

Into a denser medium (air → glass): wave slows down, bends towards the normal.

Into a less dense medium (glass → air): wave speeds up, bends away from the normal.

Frequency stays the same — only speed and wavelength change.

Refraction Diagram

💡 Memory trick: Reflection = Rebounds. Refraction = Redirects (changes direction because speed changes). All waves do both — light, sound, water waves, seismic waves, EM waves.

⏱️ 5 min

We Do

We Do: Real-World Wave Calculations 🌍

Instructions: Each card is a real-world wave. Calculate the missing value, type your answer, and check!

👥 Think-Pair-Share: Try it yourself → discuss with your partner → agree on the answer.

🐬

Dolphin Sonar

v = 1500 m/s (water)

f = 100,000 Hz

λ = ?

🏥

X-Ray

v = 3×10⁸ m/s

λ = 1×10⁻¹⁰ m

f = ?

🎸

Low E String

f = 82 Hz

v = 330 m/s (air)

λ = ?

📡

Microwave Oven

v = 3×10⁸ m/s

f = 2.45×10⁹ Hz

λ = ?

🌍

Earthquake P-wave

v = 6000 m/s

λ = 12,000 m

f = ?

🔴

Red Light

v = 3×10⁸ m/s

λ = 7×10⁻⁷ m

f = ?

Solved:

0/6

⏱️ 4 min · FLEX

I Do

I Do: Reflection & Refraction in Real Life

Remember: ALL types of waves can be reflected AND refracted. Not just light!

🪞 Reflection Examples

🔊 Echo — sound reflects off a cliff/building back to you.

🪞 Mirror — light reflects off a smooth surface. Angle in = angle out.

📡 Radar — EM waves reflect off aircraft back to the dish.

🌊 Sea wall — water waves bounce back off a harbour wall.

🌍 Seismic — earthquake waves reflect off layers inside the Earth.

🌊 Refraction Examples

🥄 Spoon in water — looks bent because light refracts at the surface.

🏊 Pool looks shallow — light bends as it leaves water → your brain misjudges depth.

🔊 Sound at night — sounds travel further because cooler air refracts sound waves downwards.

🌍 Seismic waves — refract as they pass through different rock layers (different densities).

💎 Rainbow — sunlight refracts inside water droplets, separating into colours.

🌟 Exam key point: When asked "can sound/water waves be reflected and refracted?" — the answer is always YES. All waves exhibit both behaviours. It's not just light!

⏱️ 5 min · FLEX

We Do

We Do: Reflect, Refract, or Both? 🪞🌊

Instructions: For each scenario, classify the wave behaviour. Click your answer!

👥 Think-Pair-Share: Try it yourself → discuss with your partner → agree on the answer.

1. 🗣️ You shout at a cliff and hear your voice come back.

2. 🥤 A straw in a glass of water looks bent at the surface.

3. 🌊 A wave hits a sea wall and bounces back, but some passes into the harbour and bends around the gap.

4. 📡 Radar sends EM waves that bounce off an aircraft back to the dish.

5. 🌈 Sunlight enters a raindrop, slows down, separates into colours, then exits.

6. 🌍 Earthquake waves change direction as they pass through layers of different density rock.

Correct: 0 / 6 🪞

⏱️ 8 min

Independent Work

Instructions: Complete your printed pack independently.

📝 Pack Contents:

A: Multiple Choice (4 Qs)

B: Short Answer — calculations in context + reflection/refraction

C: Long Answer — explain + compare

D: Exam-Style Question

Need help? Scaffolding sheet has key speeds, vfλ triangle, and reflection/refraction rules.

📝 Exam Command Words:
State = write a fact, no explanation needed.
Calculate = show the formula, substitute, get the answer + unit.
Explain = say what happens AND why (use "because").
Describe = say what happens step by step (no "why" needed).

🏆 Success Criteria

Foundation (Grades U–1): I can use v=fλ for sound and EM waves, and state that all waves can be reflected and refracted with examples.

Middle (Grades 1–2): I can calculate v, f, or λ in sound and EM contexts, explain reflection and refraction with diagrams, and give real-world examples for each.

Higher (Grades 3–5): I can solve multi-context problems, explain why refraction occurs in terms of speed change, and discuss how frequency/wavelength change across media boundaries.

✅ Tick as you go — Success checklist

I can define reflection and refraction

I know speed of sound (330 m/s) and EM waves (3×10⁸ m/s)

I can give real examples of each

I can explain why refraction happens (Higher)

⏱️ 3 min

Exit Ticket

Exit Ticket – Lessons 4–6 Recap

6 questions — 2 from each lesson. No notes.

🟢 I'm confident — I could teach this

🟡 I'm getting there — need a bit more practice

🔴 I'm stuck — I need help with this

1. What is the amplitude of a wave?

Maximum displacement from rest position.

2. Do waves transfer energy or matter?

Energy (and information). Not matter.

3. Write the wave speed equation.

v = f × λ

4. f = 10 Hz, λ = 2 m. Find v.

v = 10 × 2 = 20 m/s

5. State the speed of sound in air.

Approximately 330 m/s.

6. Name one example of reflection and one of refraction.

Reflection: echo / mirror. Refraction: straw in water / pool looks shallow.

Knowledge Organiser: Waves in Context (L6)

How to use: Read this before starting. Refer back during independent work. Cover it up for the exit ticket — that tests what you actually remember!

Concept	Details
v = f × λ	Works for ALL waves — sound, EM, water, seismic.
Sound in air	≈ 330 m/s. Sound in water ≈ 1500 m/s (faster).
All EM waves	3 × 10⁸ m/s in free space. Radio → gamma.
Changing medium	Speed changes, wavelength changes, frequency STAYS THE SAME.
Reflection	Wave bounces back off a surface. Angle of incidence = angle of reflection.
Refraction	Wave changes direction at a boundary because speed changes.
Into denser medium	Slows down → bends TOWARDS normal. λ decreases.
Into less dense	Speeds up → bends AWAY from normal. λ increases.
All waves	ALL waves can be reflected AND refracted — light, sound, water, seismic, EM.

🧠 Memory Tricks

Reflection = Rebounds (bounces back).

Refraction = Redirects (changes direction because speed changes).

Into denser = towards normal. Think: "Dense = Drag = pulled towards the line."

Frequency NEVER changes at a boundary — only speed and wavelength do.

Arrival Task – Foundation (U–1) 🟢

1. Write the wave speed equation.

2. f = 5 Hz, λ = 3 m. Calculate v.

3. What unit is wave speed measured in?

4. When you look in a mirror, you see yourself. When a straw is in water it looks bent. What is happening to the light?

Arrival Task – Middle (1–2) 🟠

1. v=330, f=110. Calculate λ.

2. State the speed of all EM waves.

3. Radio: λ=1500 m, v=3×10⁸. Calculate f.

4. An echo is a sound bouncing off a wall. A pool looks shallow because light bends. Name these two wave behaviours.

Arrival Task – Higher (3–5) 🔵

1. T = 0.04 s, λ = 2 m. Find v.

2. Explain why increasing f at constant v decreases λ.

3. Sound: 500 Hz. Air: 330 m/s. Water: 1500 m/s. Calculate λ in each. Why are they different?

4. Light slows entering glass. Using v=fλ, what happens to λ (f stays constant)?

Starter: Speed Check — Sound or EM?

f	λ	v = f × λ	Sound or EM?
440 Hz	0.75 m
1×10⁶ Hz	300 m
256 Hz	1.29 m
5×10¹⁴ Hz	6×10⁻⁷ m

Key: Sound ≈ 330 m/s | EM ≈ 3 × 10⁸ m/s

We Do Worksheet

Part A: Sound or EM?

For each, state if it's a sound wave or EM wave and explain how you know.

1. f=660 Hz, λ=0.5 m. Type: _______ Because: _______

2. f=1×10⁶ Hz, λ=300 m. Type: _______ Because: _______

3. f=50000 Hz, λ=0.0066 m. Type: _______ Because: _______

Part B: Context Calculations

Wave	v	f	λ
🐬 Dolphin sonar	1500 m/s	100,000 Hz	?
🎸 Guitar E string	330 m/s	82 Hz	?
📡 Microwave oven	3×10⁸ td>	2.45×10⁹ Hz	?

Part C: Reflect, Refract, or Both?

1. Echo from a cliff: _______

2. Straw looks bent in water: _______

3. Radar bouncing off aircraft: _______

4. Rainbow from sunlight through rain: _______

5. Earthquake waves changing direction in rock layers: _______

Scaffolding Sheet

Key Wave Speeds

Wave	Speed
Sound in air	≈ 330 m/s
Sound in water	≈ 1500 m/s
ALL EM waves in free space	3 × 10⁸ m/s

Cover what you want — the rest is the formula!

vfλ Triangle

Find	Formula
v	v = f × λ
f	f = v ÷ λ
λ	λ = v ÷ f

Reflection vs Refraction

	Reflection	Refraction
What happens	Wave bounces back	Wave changes direction
Why	Hits a surface	Speed changes at a boundary
Rule	Angle in = angle out	Into denser = towards normal
Example	Mirror, echo, radar	Straw in water, rainbow

Independent Work – Foundation (Grades U–1)

You've got this! Use your scaffolding sheet. Write the formula first every time. Show your working — even partial working earns marks.

Section A: Multiple Choice

1. The speed of sound in air is approximately… [ ] 3 m/s [ ] 330 m/s [ ] 3×10⁸ m/s

2. When a wave bounces off a surface, this is called… [ ] Refraction [ ] Reflection [ ] Diffraction

3. All EM waves travel at… [ ] 330 m/s [ ] Different speeds [ ] 3 × 10⁸ m/s

4. A straw looks bent in water because of… [ ] Reflection [ ] Refraction [ ] Absorption

Section B: Short Answer

5. A sound wave has f = 200 Hz and travels at 330 m/s. Calculate λ.

Hint: λ = v ÷ f = _______ ÷ _______ = _______ m

6. Name one example of sound reflection.

7. Name one example of light refraction.

Section C: Long Answer (Grade 2 Challenge — scaffolded)

8. (4 marks) Complete the sentences about reflection and refraction.

Reflection is when a wave _________________________ off a surface. [1 mark]

One example of reflection is _________________________ . [1 mark]

Refraction is when a wave changes _________________________ because its speed changes. [1 mark]

One example of refraction is _________________________ . [1 mark]

Section D: Exam-Style

9. (4 marks) A sound wave in air (330 m/s) has a frequency of 440 Hz.

(a) Calculate its wavelength. Hint: λ = v ÷ f = _______ ÷ _______ = _______ m [2 marks]

(b) The sound enters water where v = 1500 m/s. Does the frequency change? Circle: YES / NO [1 mark]

Independent Work – Middle (Grades 1–2)

Push yourself! Show full working for every calculation. Section D is your Grade 3 stretch — give it your best shot.

Section A: Recall

1. State the speed of sound in air and the speed of all EM waves.

2. When a wave enters a denser medium, what happens to: speed? wavelength? frequency?

3. Define reflection and refraction.

Section B: Application

4. Calculate the missing values:

Context	v	f	λ	Working
Ultrasound in body	1500	3×10⁶ Hz	?
FM Radio	3×10⁸	?	3 m

5. Explain, with a named example, how sound waves can be reflected. [2 marks]

Section C: Long Answer

6. (4 marks) A 500 Hz sound wave travels from air (330 m/s) into water (1500 m/s).

(a) Calculate λ in air and λ in water. [2 marks]

(b) Explain why the wavelength changes but the frequency does not. [2 marks]

Section D: Exam-Style (Grade 3 Stretch)

7. (5 marks) Light travels at 3×10⁸ m/s in air and slows to 2×10⁸ m/s in glass.

(a) Explain why the light changes direction at the boundary. [2 marks]

(b) Does it bend towards or away from the normal entering glass? [1 mark]

Independent Work – Higher (Grades 3–5)

Aim high! Full sentences for explanations. Section D includes Grade 5 challenges — these go beyond the basics. Show the examiner you can reason, not just calculate.

Section A: Recall

1. State what stays constant when a wave crosses a boundary between two media. [1 mark]

2. Explain, using the wavefront model, why a wave bends towards the normal when entering a denser medium. [3 marks]

Section B: Application

3. Complete. Show full working.

Context	v	f	λ
X-ray	3×10⁸	?	1×10⁻¹⁰ m
Earthquake P-wave	6000	?	12000 m
Sound (T=0.01 s)	330		?

4. A 440 Hz note has λ = 0.75 m in air but λ = 3.41 m in water. Calculate the speed of sound in water using these values. [2 marks]

Section C: Long Answer

5. (5 marks) Explain, using v = fλ and the concept of wavefronts, why a light wave bends towards the normal when entering glass from air. Include what happens to speed, wavelength, and frequency. [5 marks]

Section D: Exam-Style (includes Grade 5 Challenge)

6. (6 marks) Light travels from air into glass. Its speed drops from 3×10⁸ to 2×10⁸ m/s. The frequency of the light is 6×10¹⁴ Hz.

(a) Calculate λ in air. [2 marks]

(b) Calculate λ in glass. [2 marks]

Exit Ticket – Foundation (U–1) (L4–L6 Recap)

Name: _________________________ Date: _____________

1) What is amplitude?

2) Waves transfer energy or matter?

3) Write v = f × λ

4) f=10, λ=2. Find v.

5) Speed of sound in air?

6) One example of reflection + one of refraction.

Exit Ticket – Middle (1–2) (L4–L6 Recap)

1) Define wavelength + unit.

2) f=8 Hz. Calculate T.

3) v=1500, f=500. Find λ.

4) Speed of all EM waves?

5) What happens when light enters glass?

6) Can sound be reflected? Example?

Exit Ticket – Higher (3–5) (L4–L6 Recap)

1) Wavefront vs wavelength?

2) How does a tsunami carry energy without moving water?

3) T=0.05 s, λ=2 m. Find v.

4) f↑, v constant → what happens to λ?

5) 500 Hz in air (330) vs water (1500). Calculate both λ values.

6) Why does light bend towards normal entering glass?

Waves in Context & Reflection/Refraction

🖨️ Pupil Packs

⏱️ 40-Minute Pacing Guide

Arrival Task – Recall from Lesson 5

1. 🟢

2. 🟢

3. 🟢

4. Lead-in 🪞

1. 🟠

2. 🟠

3. 🟠

4. Lead-in 🪞

1. 🔵

2. 🔵

3. 🔵

4. Lead-in 🪞

Starter: Speed Check — Which Type of Wave?

📝 Calculate v, then classify:

💡 Key Speeds

💡 Did You Know?

🧠 Quick Recall (from L5)

I Do: Using v = fλ in Different Contexts (3.7)

🔊 Sound Wave Context

🌍 Why This Matters

💡 EM Wave Context

🔑 Keywords to Know

We Do: Sound or EM? Speed Detective 🔍

I Do: All Waves Can Be Reflected & Refracted (3.9)

🪞 Reflection

Reflection Diagram

🌊 Refraction

Refraction Diagram

We Do: Real-World Wave Calculations 🌍

I Do: Reflection & Refraction in Real Life

🪞 Reflection Examples

🌊 Refraction Examples

We Do: Reflect, Refract, or Both? 🪞🌊

Independent Work

📝 Pack Contents:

🏆 Success Criteria

✅ Tick as you go — Success checklist

Exit Ticket – Lessons 4–6 Recap

Knowledge Organiser: Waves in Context (L6)

🧠 Memory Tricks

Arrival Task – Foundation (U–1) 🟢

Arrival Task – Middle (1–2) 🟠

Arrival Task – Higher (3–5) 🔵

Starter: Speed Check — Sound or EM?

We Do Worksheet

Part A: Sound or EM?

Part B: Context Calculations

Part C: Reflect, Refract, or Both?

Scaffolding Sheet

Key Wave Speeds

vfλ Triangle

Reflection vs Refraction

Independent Work – Foundation (Grades U–1)

Section A: Multiple Choice

Section B: Short Answer

Section C: Long Answer (Grade 2 Challenge — scaffolded)

Section D: Exam-Style

Independent Work – Middle (Grades 1–2)

Section A: Recall

Section B: Application

Section C: Long Answer

Section D: Exam-Style (Grade 3 Stretch)

Independent Work – Higher (Grades 3–5)

Section A: Recall

Section B: Application

Section C: Long Answer

Section D: Exam-Style (includes Grade 5 Challenge)

Exit Ticket – Foundation (U–1) (L4–L6 Recap)

Exit Ticket – Middle (1–2) (L4–L6 Recap)

Exit Ticket – Higher (3–5) (L4–L6 Recap)

We Do – Class Evidence

📋 Exam Technique — Every Mark Counts!