This module covers two families of waves. The electromagnetic spectrum is a set of transverse waves that can cross a vacuum, from radio waves to gamma rays. Sound is a longitudinal wave that needs a material to travel through.
The exact list of uses, hazards and equations depends on your syllabus year. Check the current Cambridge IGCSE Physics 0625 page for your exam year. The Physics learning guide shows where this module sits in the whole subject.
What do I need to know first?
You need the wave vocabulary from wave behaviour: frequency, wavelength, amplitude and the equation wave speed = frequency × wavelength. The ideas about reflection in light and imaging help with echoes, because an echo is a reflected sound wave.
You also need to rearrange equations and keep units tidy. Most lost marks in this module come from a unit slip or from using a one-way distance when the question describes a return journey.
One orienting worked example
Lightning strikes a tree 990 m away. (Invented example data.) Take the speed of light as 3.0 × 10⁸ m/s and the speed of sound in air as 330 m/s. How long does each take to reach you?
Step 1, choose the relationship: time = distance ÷ speed for both, because each travels at constant speed.
Step 2, light: t = 990 ÷ (3.0 × 10⁸) = 3.3 × 10⁻⁶ s, which is 3.3 millionths of a second.
Step 3, sound: t = 990 ÷ 330 = 3.0 s.
Step 4, check: 330 × 3.0 = 990 m, so the sound answer is consistent. The light arrives about a million times sooner, which is why you see the flash and then wait for the thunder.
That one example shows the gap between the two families: an electromagnetic wave is enormously faster, and sound depends on the medium.
In what order should I study the lessons?
- Place a use within a spectrum region: builds the order of the regions and links each use to a property.
- Explain a safety consideration without sensationalism: links the same regions to hazards using calm, accurate wording.
- Compare sound travel in different media: moves to sound and explains why speed changes from gas to liquid to solid.
- Use echo timing with a return journey: the calculation that depends on doubling the distance.
- Interpret pitch and loudness separately: reads frequency and amplitude from a trace without mixing them up.
Then test yourself with the electromagnetic spectrum and sound practice set. After this module, charge and current starts the electricity section.
Which traps catch most students?
- Listing the regions in the wrong order, or reversing the link between frequency and wavelength.
- Choosing a use because it sounds familiar rather than because of the property of that region.
- Writing a safety answer that says “dangerous” without naming what the radiation does to the body.
- Saying sound can travel through a vacuum, or that it is fastest in gases.
- Using the full echo distance as the distance to the wall.
- Saying a louder sound has a higher pitch, when loudness relates to amplitude and pitch to frequency.
How should I use the practice set?
Write every equation and the unit on each answer line, then open the worked answer. Use the error-routing section at the end to return to the right lesson. Afterwards, log any repeated slip in the mistake log and retest queue so it returns later as a fresh question.
Some students know the facts yet lose marks at the return-journey step or in the wording of a safety answer. A teacher watching the working as it happens can spot that quickly, which is what our online one-to-one Physics tuition is designed to offer.