A radio antenna emits EM waves at a frequency of 100 MHz and an intensity of 0.2 W/m². What is the photon density in one cubic meter of the beam?

- 1.0E12 photons/cubic meter
- 1.0E16 photons/cubic meter
- 1.0E20 photons/cubic meter
- 1.4E31 photons/cubic meter
- 6.1E32 photons/cubic meter