The continuous EM spectrum (spec 3.10)
One spectrum, seven named groups.
The electromagnetic spectrum is a SINGLE CONTINUOUS RANGE of transverse waves. We divide it into named groups by approximate wavelength purely for convenience.
| Group | Approx wavelength | Approx frequency |
|---|---|---|
| Radio | > 0.1 m | < 3 GHz |
| Microwaves | 1 mm – 10 cm | 3–300 GHz |
| Infrared (IR) | 700 nm – 1 mm | 0.3 – 400 THz |
| Visible light | 400 – 700 nm | 430 – 750 THz |
| Ultraviolet (UV) | 10 – 400 nm | Hz region |
| X-rays | 0.01 – 10 nm | Hz region |
| Gamma rays | < 0.01 nm | > Hz |
Key properties shared by ALL EM waves (spec 3.10).
- They are TRANSVERSE.
- They travel at in vacuum (spec 3.10).
- They obey (spec 3.5).
- They can be reflected and refracted (spec 3.9).
- They DO NOT require a medium to travel (unlike sound).
In a material medium (glass, water, air), EM waves travel SLOWER than . The slowdown causes refraction. Numerical exam questions almost always set unless told otherwise.
- One continuous spectrum, seven named groups.
- All EM waves are transverse.
- Speed = m/s in vacuum.
- Slower in glass/water → causes refraction.