Order the electromagnetic spectrum by frequency and wavelength
Read all seven regions in both directions without confusing wave type with propagation speed.
Core and Extended; Physics 0625, 2026–2028. Follow the selected spectrum or sound section. Diagrams illustrate stated ideal models and supplied data. Written practice is self-checked.
Before you begin
- Use v = fλ.
- Recognise the visible spectrum as part of a wider range.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
At the same speed, what follows when frequency doubles?
What you will learn
- Order the seven main electromagnetic regions.
- Explain the inverse vacuum wavelength and frequency orders.
Use one ordered sequence
From low to high frequency the regions are radio, microwaves, infrared, visible, ultraviolet, X-rays and gamma rays. Microwaves occupy a radio-frequency subregion, but the syllabus lists them separately. Region boundaries are conventions rather than gaps with no radiation.
In vacuum the corresponding wavelength decreases along that same sequence. For increasing wavelength, reverse the list. Always state the quantity and direction: an unexplained list can accidentally answer the opposite ordering question.
Keep frequency separate from speed
The regions differ in frequency and vacuum wavelength, but they all have the same vacuum speed. A gamma ray does not outrun a radio wave simply because its frequency is higher. In c₀ = fλ, a larger frequency is balanced by a shorter wavelength.
Visible light is a small part between infrared and ultraviolet. Infrared lies below visible frequency; ultraviolet lies above it. These relationships help place unfamiliar uses without assuming that everything beyond human vision has the same physical effect.
Pause and explain
Which region lies between visible light and X-rays?
Worked example
Give the regions in increasing vacuum wavelength order.
Show the worked solution
- Longer wavelength corresponds to lower frequency at fixed speed.
- Start at the short-wavelength gamma-ray end.
- Reverse the increasing-frequency sequence.
Answer Gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, radio.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
List the seven main regions in increasing frequency order.
Give me a hint
Begin at the radio end and move toward gamma rays.
Compare my reasoning
- Start radio then microwaves.
- Continue infrared, visible and ultraviolet.
- End with X-rays and gamma rays.
Radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays.
Look for these in your work
- Include every region.
- Specify increasing frequency.
Order infrared, gamma rays, microwaves and ultraviolet by increasing vacuum wavelength.
Give me a hint
Reverse their relative positions in the frequency list.
Compare my reasoning
- Gamma rays have the shortest wavelength of these four.
- Ultraviolet precedes infrared in increasing wavelength.
- Microwaves finish at the longer-wavelength end.
Gamma rays, ultraviolet, infrared, microwaves.
Look for these in your work
- Use the wavelength direction.
- Retain the selected four regions only.
A learner says gamma rays arrive first because their frequency exceeds radio. Evaluate the claim for equal vacuum paths.
Give me a hint
Compare speed and path length, not just frequency.
Compare my reasoning
- Both waves share the same vacuum speed.
- The travel times equal distance divided by that speed.
- Equal path lengths therefore give equal ideal travel times.
The claim is false: equal vacuum paths give equal travel times.
Look for these in your work
- Distinguish frequency from speed.
- State the equal-path condition.
Common mistakes
- State which quantity increases.
- Higher frequency does not mean faster vacuum travel.
- Region names describe adjoining parts of a continuous spectrum.
What can you explain now?
Which has higher frequency: infrared or ultraviolet?
Compare with the explanation
Ultraviolet.
Visible lies between them, with ultraviolet at the higher-frequency side.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Give both main spectrum orders and explain why different frequency does not imply different vacuum speed.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.