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The amplitude of a wave is the maximum displacement of a point on the wave away from its undisturbed position. Free GCSE Physics notes and 15 FAQs.
Wave Characteristics: Amplitude, Wavelength & Frequency is part of Waves in air, fluids and solids in GCSE AQA Higher Physics.
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The amplitude of a wave is the maximum displacement of a point on the wave away from its undisturbed position. Free GCSE Physics notes and 15 FAQs.
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Use this lesson to stay inside Waves in air, fluids and solids while connecting the detail back to the wider Waves topic.
Read the core explanations from Wave Characteristics: Amplitude, Wavelength & Frequency before testing yourself from memory.
Waves are everywhere - from the ripples on a pond to the sound of your voice to the light hitting your eyes right now. But here's the thing: every wave, no matter how different it looks, shares the same four key characteristics.
Think of these characteristics as the 'vital statistics' of any wave. Just like you might describe a person by their height, weight, and age, we describe waves using amplitude, wavelength, frequency, and period.
These aren't just abstract concepts - they're the tools that let us understand everything from why bass notes sound different to treble, to how radio stations don't interfere with each other. Let's unlock each one.
Wave diagrams look intimidating at first, but they're actually showing you a snapshot of a wave frozen in time. The horizontal axis shows distance, and the vertical axis shows displacement from the rest position.
Here's the key insight: the wave isn't actually shaped like the diagram. A sound wave doesn't look like a wiggly line - it's compressions and rarefactions in air. The diagram shows how far particles are displaced from their normal positions.
To find amplitude, look for the highest point (crest) or lowest point (trough) and measure the vertical distance to the centre line. That centre line represents the undisturbed position - where everything would be if there was no wave.
For wavelength, pick any point on the wave pattern and measure horizontally to where that exact same pattern repeats. Crest to crest is easiest, but trough to trough works equally well. You could even measure from any point on the upward slope to the equivalent point on the next upward slope.
Worked example: Reading Amplitude and Wavelength from a Wave Diagram
A wave diagram shows a wave with crests at 2.0 cm above the centre line and troughs at 2.0 cm below. The distance from one crest to the next crest is 8.0 cm. Find the amplitude and wavelength.
Answer: Amplitude = 2.0 cm, Wavelength = 8.0 cm
Frequency and period are like two sides of the same coin - they're measuring the same thing in opposite ways. Frequency asks 'how many waves per second?' while period asks 'how many seconds per wave?'
Think about it this way: if 4 waves pass you every second (frequency = 4 Hz), then each individual wave takes 1/4 of a second to pass (period = 0.25 s). The faster the waves come (higher frequency), the less time each one takes (shorter period).
This relationship is captured in one of the most important equations in wave physics. It's beautifully simple, but students often get confused about which way round it goes.
The equation can be rearranged to find frequency if you know period: $f = \frac{1}{T}$. Notice how they're reciprocals - as one gets bigger, the other gets smaller. High frequency means short period, low frequency means long period.
Worked example: Calculating Period from Frequency
A radio wave has a frequency of 100 MHz (100 × 10⁶ Hz). Calculate its period. [3 marks]
Answer: $T = 1.0 \times 10^{-8}\,s$
Understanding wave characteristics isn't just academic - it explains phenomena you experience every day. The deep bass from a subwoofer has large amplitude (loud) and long wavelength (low frequency). The high-pitched whine of a mosquito has small amplitude but very short wavelength (high frequency).
In water, amplitude determines how dangerous waves are to surfers - bigger amplitude means more energy. Wavelength affects how waves behave near the shore - long wavelength waves (like tsunamis) can travel across entire oceans without losing much energy.
Light waves follow the same rules. Red light has longer wavelength than blue light, which is why red light can penetrate fog better. The amplitude of light waves determines brightness - more amplitude means brighter light.
Even in your mobile phone, radio waves with different frequencies carry different information. Radio waves can carry information by varying the signal.
Wave questions in GCSE exams follow predictable patterns. You'll either be given a diagram to analyse, or data to calculate with. The key is recognising which characteristic they're asking for and using the right approach.
For diagram questions, always use a ruler. Measure carefully and show your working. Examiners give method marks even if your final answer is slightly wrong due to measurement errors. State what you're measuring - 'from crest to crest' or 'from centre line to maximum displacement'.
For calculation questions, the formula $T = \frac{1}{f}$ is your best friend. But watch out for unit traps - frequency might be given in kHz or MHz, and you'll need to convert to Hz. Period might be given in milliseconds, requiring conversion to seconds.
Common mistakes include confusing amplitude with wavelength (amplitude is vertical displacement, wavelength is horizontal distance), and mixing up frequency with period (high frequency means short period, not long period).
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The amplitude of a wave is the maximum displacement of a point on the wave away from its undisturbed position. On a wave diagram, measure the vertical distance from the centre line to a crest or trough; crests 2.0 cm from the centre line give an amplitude of 2.0 cm.
Wavelength is the distance from a point on one wave to the equivalent point on the adjacent wave. Crest to crest is easiest to measure, so if the distance from one crest to the next is 8.0 cm, the wavelength is 8.0 cm.
The frequency of a wave is the number of waves passing a point each second, measured in hertz (Hz). Frequency asks 'how many waves per second?', while period asks 'how many seconds per wave?'.
Period and frequency are reciprocals: T = 1/f and f = 1/T. If 4 waves pass each second (frequency 4 Hz), each wave takes 0.25 s to pass, so high frequency means a short period.
To calculate the period, convert the frequency to Hz, then use T = 1/f. A radio wave with a frequency of 100 MHz (100 × 10⁶ Hz) has a period of 1 ÷ (100 × 10⁶) = 1.0 × 10⁻⁸ s.
Amplitude is a vertical displacement, from the centre line to a crest or trough, while wavelength is a horizontal distance, from one point on a wave to the equivalent point on the next. Confusing the two is a common mistake.
A crest is the highest point of a wave and a trough is the lowest point. The amplitude is the vertical distance from the centre line to either, and the wavelength can be measured crest to crest or trough to trough.
Amplitude is measured from the centre line, the undisturbed position, to a crest or trough, as a vertical distance. A wave with crests 2.0 cm from the centre line has an amplitude of 2.0 cm.
Wavelength is measured horizontally from any point on the wave to where the same pattern repeats, most easily crest to crest or trough to trough. If crests are 8.0 cm apart, the wavelength is 8.0 cm.
A 100 MHz radio wave has a period of 1.0 × 10⁻⁸ s. Converting 100 MHz to 100 × 10⁶ Hz, T = 1/f = 1 ÷ (100 × 10⁶) = 1.0 × 10⁻⁸ s.
If 4 waves pass each second, the frequency is 4 Hz and each wave takes 1/4 of a second, so the period is 0.25 s. Period and frequency are reciprocals: T = 1/f.
Amplitude affects how loud a sound is and how bright light is: a deep bass note from a subwoofer has a large amplitude, and more amplitude means brighter light. For water waves, bigger amplitude means more energy.
Red light can penetrate fog better than blue light because it has a longer wavelength. Light waves follow the same rules as other waves, and their amplitude determines brightness.
High frequency means a short period, and low frequency means a long period, because T = 1/f. Mixing these up is a common mistake: 4 waves per second (4 Hz) gives a period of 0.25 s.
Frequencies in kHz or MHz must be converted to Hz before using T = 1/f: 100 MHz is 100 × 10⁶ Hz. A period given in milliseconds must also be converted to seconds.