Properties of Waves | Physics

📖 In-Depth Theory

Wave Properties

KEY WAVE PROPERTIES:

AMPLITUDE (A): maximum displacement of a particle from its equilibrium (undisturbed) position.

Measured in metres (m). Relates to energy — larger amplitude = more energy.

WAVELENGTH (λ, lambda): distance from one point on a wave to the equivalent point on the next wave.

For example: crest to crest, or trough to trough, or compression to compression.

Measured in metres (m).

FREQUENCY (f): number of complete waves passing a point per second.

Measured in HERTZ (Hz). 1 Hz = 1 complete wave per second.

PERIOD (T): time for one complete wave to pass a point.

Measured in seconds (s).

Relationship: T = 1 ÷ f (or f = 1 ÷ T)

The Wave Equation

WAVE SPEED EQUATION:

v = f × λ

v = wave speed (m/s)

f = frequency (Hz)

λ = wavelength (m)

Rearranging:

f = v ÷ λ

λ = v ÷ f

EXAMPLE 1:

Sound wave: frequency 440 Hz, speed 340 m/s:

λ = 340 ÷ 440 = 0.77 m

EXAMPLE 2:

EM wave: wavelength 0.1 m, speed 3 × 10⁸ m/s:

f = 3 × 10⁸ ÷ 0.1 = 3 × 10⁹ Hz = 3 GHz (microwave range)

All EM waves travel at the SAME speed in vacuum: c = 3 × 10⁸ m/s.

Sound in air: ~340 m/s at room temperature.

Measuring Wave Speed — Required Practical

REQUIRED PRACTICAL (RP19) — Measure wave speed:

METHOD 1 — Water waves (ripple tank):

Use a stroboscope to 'freeze' waves.

Measure wavelength from the still image.

Count frequency from the vibrating bar setting.

Calculate: v = fλ.

METHOD 2 — Sound waves:

Connect a microphone to an oscilloscope.

Display the waveform — measure period T from the trace.

f = 1/T.

Using two microphones and measuring time delay to find speed.

EXAM SKILL — reading oscilloscope traces:

Time per division (x-axis) → period T → frequency f = 1/T.

Volts per division (y-axis) → amplitude.

⚠️ Common Mistake

Amplitude is the distance from the equilibrium (centre) to the crest — NOT from crest to trough (that's double the amplitude). Frequency and period are reciprocals: f = 1/T. Don't confuse wavelength (one full cycle length) with amplitude (height from centre).

📐 Variables

vWave speed (v) is measured in m/s (m/s)

fFrequency (f) is measured in hertz (Hz)

λWavelength (λ) is measured in metres (m)

TPeriod (T) is measured in seconds (s)

AAmplitude (A) is measured in metres (m)

📐 Key Equations

v = f × λ

T = 1 ÷ f

📌 Key Note

Amplitude: equilibrium to crest (m). Wavelength (λ): crest to crest (m). Frequency (f): waves per second (Hz). Period (T): seconds per wave. T = 1/f. v = fλ. EM waves in vacuum: 3×10⁸ m/s. Sound in air: ~340 m/s. RP19: measure wave speed in ripple tank.

🎯 Matching Activity — Wave Property Definitions

Match each wave property to its definition and unit. — drag the symbols on the right to match the component names on the left.

Amplitude

Drop here

Wavelength (λ)

Drop here

Frequency (f)

Drop here

Period (T)

Drop here

Wave speed (v)

Drop here

Number of complete waves per second — hertz (Hz)

v = f × λ — distance travelled per second in m/s

Time for one complete wave — seconds; T = 1/f

Distance from one crest to the next — metres

Maximum displacement from equilibrium — measured in metres

⚽ FIFA Worked Examples

Wave Equation

A sound wave has frequency 500 Hz and travels at 340 m/s. Calculate its wavelength.

F

v = f × λ, so λ = v ÷ f

I

v = 340 m/s, f = 500 Hz

F

λ = 340 ÷ 500

A

λ = 0.68 m

🧪 Required Practical

🔬 RP19 (Physics) — Measure the speed of waves in a ripple tank using v = fλ. Measure frequency and wavelength of waves. Also: measure speed of sound using microphones and oscilloscope.

Know the method, variables, equipment and how to analyse results.

🎯 Test Yourself

Question 1 of 2

1. A wave has frequency 200 Hz. What is its period?

2. A radio wave has wavelength 3 m. What is its frequency? (speed of EM waves = 3 × 10⁸ m/s)

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I'll use CFIFA for calculations and flag Higher/Triple content clearly.