# Types of Waves

## Types of Waves Revision

**Types of Waves **

**Waves** **transfer energy** from one place to another. There are many different types of waves, from **mechanical **waves and **sound **waves to **electromagnetic** waves, all of which can be used for different things.

**Transverse and Longitudinal Waves**

When a wave travels through a **medium** (e.g. air or water), the particles in that medium **vibrate**. The particles transfer **energy** from one another as they vibrate. This transfers energy between particles but the particles themselves stay in the same place.

Remember: **waves transfer energy but not matter**.

In **transverse waves**, the vibrations of the particles are **perpendicular** to the direction of energy transfer.

Transverse waves have **crests** and **troughs **where particles have been displaced a maximum amount from their positions.

Examples of transverse waves are water waves, waves on a string, and electromagnetic waves.

In **longitudinal waves**, vibrations of the particles are **parallel **to the direction of energy transfer.

Longitudinal waves have **compressions** where particles are squashed together, and **rarefactions **where particles spread apart due to the vibrations.

Examples of longitudinal waves are sound waves and seismic P-waves.

**Properties of Waves**

You need to know the following wave properties:

**Amplitude**– the maximum displacement of a point on the wave from its undisturbed position.**Wavelength**– the distance from a point on one wave to the equivalent point on the next wave (e.g. crest-to-crest or trough-to-trough).**Frequency**– the number of waves passing a point per second.

You need to be able to calculate other wave properties.

Firstly, the** period** of a wave is the amount of time it takes a complete wave to pass a point. It can be calculated using the following equation:

\textcolor{f21cc2}{T=\dfrac{1}{\text{f}}}

**T**is the**t****ime period**in**seconds**\text{(s)}.**f**is the**frequency**in**Hertz**\text{(Hz)}.

The wave speed is the speed at which energy is transferred through the medium. It can be calculated using:

\textcolor{f21cc2}{v=f \lambda}

**v**is the**velocity**in**metres per second**\text{(m/s)}.**f**is the**frequency**in**hertz**\text{(Hz)}.**\lambda**is the**wavelength**in**metres**\text{(m)}.

**Changing Wave Properties**

Wave properties are **inter-related**. This means that if you change one wave property, another may change too.

For example, if you **increase the frequency** of a wave, you also **increase the wave velocity** and **decrease the period**.

If you **increase the wavelength** (whilst keeping the frequency constant) you also increase the **wave velocity**.

**Example: Calculating Wave Properties**

A wave has wavelength 50\text{ cm} and wave speed 300\text{ m/s}. Calculate the frequency and period of this wave.

**[4 marks]**

To calculate f, we need the equation:

v=f\lambda

Rearrange for f:

\begin{aligned}f&=\dfrac{v}{\lambda} \\ &=\dfrac{\textcolor{f21cc2}{300}}{\textcolor{aa57ff}{0.5}} \\ &= \bold{600\textbf{ Hz}} \end{aligned}

Now calculate the period:

\begin{aligned}T&=\dfrac{1}{f} \\ &=\dfrac{1}{600} \\ &=\bold{0.002}\textbf{ s} \text{ (1 sf)} \end{aligned}

## Types of Waves Example Questions

**Question 1:** What is the difference between transverse and longitudinal waves?

**[2 marks]**

In transverse waves, the direction of vibration is **perpendicular** to the direction of energy transfer whereas in longitudinal waves, the direction of vibration is **parallel** to the direction of energy transfer.

**Question 2:** Is the following statement true or false? Explain your answer.

“*Waves transfer energy and matter*“?

**[2 marks] **

**False. **

**Waves transfer energy but not matter. **

**Question 3:** What is the wave velocity of a wave with frequency 5\text{ Hz} and wavelength 2\text{ m}?

**[2 marks]**

**Question 4:** If the frequency of a wave is 10\text{ Hz}, what is the period of the sound wave?

**[2 marks]**

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