| English | Electromagnetic spectrum |
|---|---|
| Bahasa Melayu | Spektrum elektromagnet |
| 中文 | 电磁波谱 |
Definition
The full range of electromagnetic waves arranged by frequency or wavelength, from radio waves to gamma rays, all travelling at the speed of light in a vacuum.
In exam terms
The electromagnetic spectrum is the complete family of electromagnetic waves arranged in order of increasing frequency (or decreasing wavelength): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
All members are transverse waves that need no medium and travel at the same speed in a vacuum, c = 3.0 × 10⁸ m s⁻¹. They obey v = fλ, so a higher frequency means a shorter wavelength.
A correct sentence: gamma rays have the highest frequency and shortest wavelength in the electromagnetic spectrum. Frequency is measured in hertz (Hz) and wavelength in metres (m).
Do not confuse it with sound waves
Do not confuse electromagnetic waves with sound waves. Sound is a longitudinal mechanical wave that must travel through a medium and cannot pass through a vacuum; electromagnetic waves are transverse and travel through a vacuum.
So sound is not part of the electromagnetic spectrum.
In Paper 2, a question that says state the order of the electromagnetic spectrum wants the seven regions in the correct sequence, while explain why we can see stars asks you to say that light reaches us through the vacuum of space because electromagnetic waves need no medium.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)