EM Waves and Communication Flashcards
EM waves with different wave lengths have different _______
EM waves with different wave lengths have different PROPERTIES
How many basic types of EM waves are there?
7
The different regions of EM waves ______ to form a ______ _______
The different regions of EM waves MERGE to form a CONTINUOUS SPECTRUM
What is the range of wavelengths of EM waves?
10^-5 m to more than 10^4 m
Do EM waves all travel at the same speed through a vacuum?
YES
What is the speed all EM waves travel through a vacuum?
3 x 10^8 m/s
Will an EM wave with a higher frequency have a shorter wavelength or a longer wavelength?
An EM wave with a HIGHER frequency will have a SHORTER wavelength
Will an EM wave with a lower frequency have a shorter wavelength or a longer wavelength?
An EM wave with a lower frequency will have a longer wavelength
Because of their different properties, EM waves are used for different _______
Because of their different properties, EM waves are used for different PURPOSES
Radio waves are mainly used for ______
Radio waves are mainly used for COMMUNICATION
Radio waves have wave lengths longer than about ____
Radio waves have wave lengths longer than about 10cm
How long are the wavelengths of long-wave radio?
Between 1 - 10 km
What can long-wave radio do?
Be received halfway round the world from its start point
Why can long-wave radio be picked up far from where they were emitted?
Because long wavelengths DIFFRACT around the curved surface of the Earth
What 2 other things can long-wave radio also diffract around/ into?
- Hills
- Tunnels
etc
What does the diffraction effect of long-wave radio wavelengths make it possible to do?
Receive radio signals even when TRANSMITTER isn’t in the LINE OF SIGHT of the RECEIVER
What length wavelengths are the radio waves used for TV and FM radio transmissions?
Very short
What effect does the short wavelength of the radio waves used for TV and FM radio transmissions on reception? Why?
To get reception you must be in DIRECT SIGHT of the transmitter- Doesn’t diffract around hills or travel far through buildings
What can’t short wavelengths do that long wavelengths can?
Diffract around the Earth, around hills, into tunnels etc
What is the wavelength of short-wave radio signals?
About 10m - 100m
How can short-wave radio signals be received out of the line of sight of the transmitter?
They can be REFLECTED from the IONOSPHERE
What is the ionosphere?
An electrically charged layer in the Earth’s upper atmosphere
What type of medium-wave signals can reflect from the ionosphere
The SHORTER ones
What does reflecting medium-wave signals off the ionosphere depend on? (2)
- Atmospheric conditions
2. The time of day
