radio waves & communication
radio waves are used to broadcast tv and radio signals and to transmit satellite signals
long-waves radio (wavelength of 1 - 10km) can be transmitted from London and received halfway round the world.
that's because long wavelengths bend around the curved surface of the earth
the radio waves used for tv and fm radio transmissions have very short wavelengths (10cm - 10m).
to get reception, you must be in direct sight of the transmitter - the signal doesn't bend around hills or travel far through buildings
short-wave radio signals (wavelengths of about 10m - 100m) can, like long-wave be received at long distances from the transmitter.
that's because they are reflected from the ionosphere - an electrically charged layer in the earth's upper atmosphere.
medium wave signals can also reflect from the ionosphere, depending on atmospheric conditions and time of day
some very short-wave radio waves can pass though the ionosphere - so they can be used for satellite communications
communication to and from satellites use microwaves. but you need to use microwaves which can pass easily through the earths watery atmosphere
for satellite tv, the signal from a transmitter is transmitted into space where it's picked up by the satellite receiver dish orbiting thousands of kilometres above the earth.
the satellite transmits the signal back to earth in a different direction where it's received by a satellite dish on the ground.
there is a slight time delay between the signal being sent and received
mobile phone signals also travel from your phone to the nearest transmitter as microwaves
in microwave ovens, the microwaves need to be absorbed by the water molecules in food to be able to heat it up - so they use a different wavelength to those used in satellite communications
the microwaves penetrate up to a few into the food before being absorbed by water molecules. the energy from the absorbed microwaves causes the food to heat up. the heat energy is then conducted or convected to other parts of the food