Question

The New Horizons space probe flew by Pluto in July of 2015 and sent back the first high-resolution images of its surface. Due to the distance between Pluto and Earth at that time, it took 4.5 hours to receive the radio waves which travel at the speed of light (c=3.0x108m/s). New Horizons transmits signals with a radio antenna that are received on Earth with a 35 m radius satellite dish. The dish can detect signals as weak as 5.0x10-15 W. If New Horizons’ antenna emits radio waves in all directions equally, what power output does the antenna need to have for the signals to be detected with the satellite dish on Earth?

Answer 1