Edexcel iGCSE Physics -3.5–3.6 Wave Speed, Frequency, Wavelength, and Time Period- Study Notes- New Syllabus

Wave Speed, Frequency and Wavelength

The speed at which a wave travels depends on how frequently the wave oscillates and the distance between successive wavefronts. This relationship applies to all types of waves, including sound waves, water waves, and electromagnetic waves.

Key Relationship

The relationship between wave speed, frequency and wavelength is:

\( \mathrm{wave\ speed = frequency \times wavelength} \)

\( \mathrm{v = f \times \lambda} \)

• \( \mathrm{v} \) = wave speed (m/s)
• \( \mathrm{f} \) = frequency (Hz)
• \( \mathrm{\lambda} \) = wavelength (m)

Understanding the Equation

• Frequency tells how many waves pass a point each second.
• Wavelength tells how long each wave is.
• Multiplying them gives the distance travelled per second.

This distance per second is the wave speed.

What Happens if One Quantity Changes

• If frequency increases and wave speed stays constant, wavelength decreases.
• If wavelength increases and wave speed stays constant, frequency decreases.
• In a given medium, wave speed is usually constant.

Applies to Different Types of Waves

• Sound waves: speed depends on the medium.
• Water waves: speed depends on water depth.
• Light waves: speed depends on the medium (vacuum or material).

Key Idea

• Wave speed links frequency and wavelength.
• The equation works for all waves.
• Correct units must always be used.

Important Points to Remember

• Use Hz for frequency and metres for wavelength.
• Wave speed is always in m/s.
• Rearrange the equation carefully when needed.

Rearranging the Formula

• Frequency: \( \mathrm{f = \dfrac{v}{\lambda}} \)
• Wavelength: \( \mathrm{\lambda = \dfrac{v}{f}} \)