EM Waves

Transverse waves. Can travel through Vacuum.

All travel at same speed in vacuum : 3 × 10^8 ms^-1. This number is given its own symbol - ‘c’

In air, speed of EM waves is almost c

EM Waves consist of transverse oscillating electric (E) and magnetic (B) fields.

Oscillating E and B fields always at right angles to each other - waves produced in the 2 fields travel at same speed

Direction of polarization = direction parallel to the E field of wave

Transverse waves can be plane polarised - only oscillating in one plane

Range of visible wavelengths: 700nm (red) to 400 nm (violet)

X-ray and gamma defined by source - fast-moving e- vs unstable atomic nuclei

Radiowaves = m-km (>10^6)

Microwaves = mm - micrometer (10^-1 to 10^-3)

Infrared = 10^-3 to 700nm

Ultraviolet = 400nm to 100nm

X-rays = 100nm to 1picometer

Gamma = 1picometer to greater than 10^-16m

Atomic radius = 10^-10m

Nuclear radius = 10^-15m

Only certain EM Waves transmitted through atmosphere: some radio (10cm to 10m), visible, longer wavelengths of UV, and the rest are absorbed or reflected by atmosphere. This is why telescopes often on mountains or in orbit around Earth.