Topic 3.1 : General Properties of Waves

🔑 1. Waves Transfer Energy (NOT Matter)

✅ Definition

A wave is a way of transferring energy from one place to another without transferring matter.

💡 Key Idea

Particles vibrate in position but do not travel with the wave.
Energy moves, not the particles.

🧪 Example:

Water waves: water particles move up and down, but water doesn’t travel across the tank.
Sound waves: air particles vibrate, but air does not move from source to ear.

🪢 2. Wave Motion (Ropes, Springs, Water)

🧠 What is Wave Motion?

Wave motion is the movement of a disturbance through a medium caused by vibrations.

🧪 Examples:

(a) Rope:

Shake one end → wave travels along rope
Rope moves up/down, wave moves sideways

(b) Spring (Slinky):

Push and pull → compressions move along spring

(c) Water Waves:

Drop a stone → ripples spread outward

👉 In all cases:

Energy travels
Particles only oscillate

📊 3. Features of a Wave

🧾 Key Terms You MUST Know:

Term	Definition
Wavefront	Line joining points in phase (same position in wave)
Wavelength (λ)	Distance between two identical points (e.g. crest to crest)
Frequency (f)	Number of waves passing per second (Hz)
Amplitude	Maximum displacement from rest position
Wave speed (v)	Speed at which wave travels
Crest (Peak)	Highest point of wave
Trough	Lowest point of wave

💡 Important Relationships:

Higher amplitude → more energy
Higher frequency → more waves per second

⚡ 4. Wave Equation

✅ Formula:

Where:

( v ) = wave speed (m/s)
( f ) = frequency (Hz)
( λ ) = wavelength (m)

🧪 Example:

If:

( f = 5 , Hz )
( \lambda = 2 , m )

Then:

📌 Exam Tips (Wave Equation)

Rearranging is common:
Always include units

↕️ 5. Transverse Waves

✅ Definition

A transverse wave has vibrations perpendicular (at right angles) to the direction of wave travel.

📌 Examples:

Water waves
Light (electromagnetic waves)
Seismic S-waves

💡 Key Features:

Have crests and troughs
Can be polarised (extra concept sometimes tested)

↔️ 6. Longitudinal Waves

✅ Definition

A longitudinal wave has vibrations parallel to the direction of wave travel.

📌 Examples:

Sound waves
Seismic P-waves

💡 Key Features:

Compressions (high pressure)
Rarefactions (low pressure)

🧠 Key Difference

Feature	Transverse	Longitudinal
Direction of vibration	Perpendicular	Parallel
Shape	Crests & troughs	Compressions & rarefactions

🔁 7. Wave Behaviours

🪞 (a) Reflection

✅ Definition

Reflection is when a wave bounces off a surface.

📌 Key Law:

Angle of incidence = Angle of reflection

🧪 Example:

Water waves hitting a barrier
Light reflecting off a mirror

🌊 (b) Refraction

✅ Definition

Refraction is the change in direction of a wave due to a change in speed.

💡 Key Idea:

When waves enter a different medium:
- Speed changes
- Wavelength changes
- Frequency stays the same

🧪 Example:

Water waves entering shallow water → slow down → bend

🔀 (c) Diffraction

✅ Definition

Diffraction is the spreading out of waves when they pass through a gap or around an edge.

🧪 Example:

Water waves passing through a narrow gap
Sound spreading through a doorway

🧪 8. Ripple Tank Experiments

A ripple tank is used to study water waves.

🔬 Shows:

(a) Reflection

Waves bounce off barrier

(b) Refraction

Use shallow region → waves slow and bend

(c) Diffraction (Gap)

Waves spread after passing through gap

(d) Diffraction (Edge)

Waves bend around obstacle

📏 9. Diffraction Through a Gap

💡 Depends on:

1. Wavelength:

Longer wavelength → more diffraction

2. Gap size:

Smaller gap → more diffraction

📊 Key Rule:

Maximum diffraction occurs when:

📐 10. Diffraction at an Edge

Longer wavelength → more spreading around edge
Shorter wavelength → less noticeable bending

🧠 Summary Table

Property	Effect
Larger wavelength	More diffraction
Smaller gap	More diffraction
Change in medium	Refraction occurs
Smooth surface	Reflection occurs

🔑 1. Waves Transfer Energy (NOT Matter)​

✅ Definition​

💡 Key Idea​

🧪 Example:​

🪢 2. Wave Motion (Ropes, Springs, Water)​

🧠 What is Wave Motion?​

🧪 Examples:​

(a) Rope:​

(b) Spring (Slinky):​

(c) Water Waves:​

📊 3. Features of a Wave​

🧾 Key Terms You MUST Know:​

💡 Important Relationships:​

⚡ 4. Wave Equation​

✅ Formula:​

Where:​

🧪 Example:​

📌 Exam Tips (Wave Equation)​

↕️ 5. Transverse Waves

✅ Definition​

📌 Examples:​

💡 Key Features:​

↔️ 6. Longitudinal Waves

✅ Definition​

📌 Examples:​

💡 Key Features:​

🧠 Key Difference​

🔁 7. Wave Behaviours

🪞 (a) Reflection​

✅ Definition​

📌 Key Law:​

🧪 Example:​

🌊 (b) Refraction​

✅ Definition​

💡 Key Idea:​

🧪 Example:​

🔀 (c) Diffraction​

✅ Definition​

🧪 Example:​

🔬 Shows:​

(a) Reflection​

(b) Refraction​

(c) Diffraction (Gap)​

(d) Diffraction (Edge)​

📏 9. Diffraction Through a Gap

💡 Depends on:​

1. Wavelength:​

2. Gap size:​

📊 Key Rule:​

📐 10. Diffraction at an Edge

🧠 Summary Table

🎯 Final Exam Tips

✅ Common Mistakes:​

📝 How to Answer 3–4 Mark Questions:​

🔑 1. Waves Transfer Energy (NOT Matter)

✅ Definition

💡 Key Idea

🧪 Example:

🪢 2. Wave Motion (Ropes, Springs, Water)

🧠 What is Wave Motion?

🧪 Examples:

(a) Rope:

(b) Spring (Slinky):

(c) Water Waves:

📊 3. Features of a Wave

🧾 Key Terms You MUST Know:

💡 Important Relationships:

⚡ 4. Wave Equation

✅ Formula:

Where:

🧪 Example:

📌 Exam Tips (Wave Equation)

✅ Definition

📌 Examples:

💡 Key Features:

✅ Definition

📌 Examples:

💡 Key Features:

🧠 Key Difference

🪞 (a) Reflection

✅ Definition

📌 Key Law:

🧪 Example:

🌊 (b) Refraction

✅ Definition

💡 Key Idea:

🧪 Example:

🔀 (c) Diffraction

✅ Definition

🧪 Example:

🔬 Shows:

(a) Reflection

(b) Refraction

(c) Diffraction (Gap)

(d) Diffraction (Edge)

💡 Depends on:

1. Wavelength:

2. Gap size:

📊 Key Rule:

✅ Common Mistakes:

📝 How to Answer 3–4 Mark Questions: