The Voyager 1 spacecraft is at the edge of the solar system, about 11 billion km away. (a) How
long does a radio signal from Voyager 1 take to get to the Earth? (b) Its radio works at 8 GHz.
What is the wavelength? (c) What type of light is this? (d) What is the energy of 1 photon? (e)
It has a 23 watt radio wave transmitter. How many photons per second is this? (f) This radio
wave is aimed towards the Earth by a dish; by the time the signal gets to the Earth, the area of
the radio beam is 4x10^15 km^2
What is the photon flux density, in photons per second per square
km? (g) How about in photons per second per square meter?