Unit Overview
Waves
CIE A-Level PhysicsΒ· 5 min read π n/a
1. Unit at a Glance
This unit builds from the basic definition of wave motion up to specialized properties like polarisation. We start by defining progressive waves and distinguishing between the two main types of waves, then learn how to quantify waves using standard parameters.
Next we cover the universal wave equation, the electromagnetic spectrum, wave intensity, and end with polarisation. All concepts in this unit are prerequisite for understanding superposition, interference, and standing waves in the next unit.
This unit is split into the following sequential sub-topics:
Progressive waves
Learn what a progressive wave is and how it transfers energy without transferring matter.
β β β± 8 min
Transverse and longitudinal waves
Distinguish between the two main classes of waves with common examples of each.
β β β± 7 min
Wave parameters
Define and calculate key properties: displacement, amplitude, wavelength, period, frequency, and phase difference.
β β β β± 10 min
Wave equation
Use the wave equation to solve for unknown wave speed, frequency, or wavelength.
β β β± 8 min
Electromagnetic spectrum
Order EM spectrum regions by wavelength, frequency, and energy, and list common uses for each.
β β β± 9 min
Wave intensity
Relate wave intensity to amplitude and distance from the source using the inverse square law.
β β β β± 7 min
Polarisation
Explain polarisation of transverse waves, Malus's law, and practical applications.
β β β β β± 10 min
2. Common Pitfalls
Wrong move:
Mixing up which wave properties affect intensity
Why:
Many students incorrectly assume higher frequency equals higher intensity, ignoring the dependence on amplitude.
Correct move:
Remember intensity is proportional to the square of amplitude, and proportional to the square of frequency for a given amplitude.
Wrong move:
Forgetting all EM waves travel at the same speed in a vacuum
Why:
Students often assume higher frequency EM waves travel faster than lower frequency ones.
Correct move:
All electromagnetic waves travel at m/s in a vacuum, regardless of frequency or wavelength.
Wrong move:
Thinking longitudinal waves can be polarised
Why:
Polarisation requires vibration perpendicular to the direction of travel, which does not occur in longitudinal waves.
Correct move:
Only transverse waves can be polarised; longitudinal waves cannot be polarised.
3. Quick Reference Cheatsheet
Concept | Formula / Key Fact |
|---|---|
Wave speed relationship | |
Frequency and period conversion | |
Intensity vs amplitude | |
Inverse square law for intensity | |
Speed of EM waves in vacuum | m/s |
Malus's law for polarisation | |
Polarisation rule | Only transverse waves can be polarised |
Progressive wave property | Energy is transferred, matter is not displaced |
What's Next
Start with the first sub-topic of this unit to build your foundational understanding of wave motion. Once you complete all sub-topics here, you will be ready to move on to the next unit on superposition, which directly builds on all the wave concepts you will learn in this unit.