The speed of electromagnetic waves is the same for all waves regardless of wavelength
A typical analog cell phone has a frequency of 850 MHz; a digital phone a frequency of 1950
MHz. Compared to the signal from an analog phone, the digital signal has shorter wavelength
and higher photon energy.
A radio tower emits two 50 W signals, one an AM signal at a frequency of 850 kHz, one an FM
signal at a frequency of 85 MHz. Which signal has more photons per second?
FM: higher frequency → higher photon energy
Therefore the AM signal has more photons per second
Energy and Field Strength
Intensity of an electromagnetic wave with field amplitudes 0 and B0
P 2 c 2
I = A = ½ ϵ 0 0 ½ μ 0 B 0
Amplitude of magnetic field typically small
E 0 √cε 0
E 0 cB 0
The Microwave Oven
Inside the cavity of a microwave oven, the 2.4 GHz electromagnetic waves have an
intensity of 5.0 kW/m2
What is the strength of the electric field?
I = 5.0 x 10 W/m
The magnetic field? 6.5 μT