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P6 G) Electromagnetic Spectrum – Part 2
P6 G) Electromagnetic Spectrum – Part 2
Electromagnetic (EM) waves are made up of oscillating electric and magnetic fields. The aerial that produces a radio wave is known as a transmitter. A transmitter produces a radio wave when an alternating current passes through an aerial. The AC supply causes the charges in the transmitter to oscillate which produces an electric and magnetic field – this is our radio wave. The frequency of the radio wave produced will be equal to the frequency of the AC supply. The wave produced will travel through the atmosphere.
Some of these radio waves will reach a second aerial where they will be absorbed by the electrons; the second aerial is known as the receiver. The energy that is absorbed by the electrons in the receiver causes the electrons to oscillate at the same frequency as the transmitter. If the receiver is part of a complete circuit, the oscillating electrons will produce an AC current with the same frequency as the transmitter.
The diagram below shows what is happening at the transmitter and the receiver.
Some of these radio waves will reach a second aerial where they will be absorbed by the electrons; the second aerial is known as the receiver. The energy that is absorbed by the electrons in the receiver causes the electrons to oscillate at the same frequency as the transmitter. If the receiver is part of a complete circuit, the oscillating electrons will produce an AC current with the same frequency as the transmitter.
The diagram below shows what is happening at the transmitter and the receiver.
There is an oscilloscope on the transmitter that shows us the wave from the AC current. This AC current causes the electrons in the transmitter to oscillate, which causes a radio wave to be produced.
When the radio waves hit the receiver, energy is absorbed by the electrons which causes them to oscillate. If the receiver is part of a complete circuit, the oscillating electrons will produce an AC current. We can connect an oscilloscope to the receiver, and we will see that the AC current produced at the receiver has the same frequency as the AC supply at the transmitter.
When the radio waves hit the receiver, energy is absorbed by the electrons which causes them to oscillate. If the receiver is part of a complete circuit, the oscillating electrons will produce an AC current. We can connect an oscilloscope to the receiver, and we will see that the AC current produced at the receiver has the same frequency as the AC supply at the transmitter.
Radio Waves & Communication
Radio waves have the longest wavelength out of all the EM waves. Their wavelengths range from 10 cm to 10 km. Different radio waves have different properties and therefore different uses.
Long-wave radio waves can transmit information from the UK to the other side of the world. They can do this because the long-wave radio waves bend/ diffract around the earth’s surface. They can also go inside tunnels and diffract around hills. Long-wave radio waves have a wavelength between 1 km and 10 km. Long-wave radio waves are able to be received even if the receiver isn’t in the line of site of the transmitter; this is because the long-wave radio waves will diffract. A diagram showing long-wave radio waves being diffracted is shown below.
Radio waves have the longest wavelength out of all the EM waves. Their wavelengths range from 10 cm to 10 km. Different radio waves have different properties and therefore different uses.
Long-wave radio waves can transmit information from the UK to the other side of the world. They can do this because the long-wave radio waves bend/ diffract around the earth’s surface. They can also go inside tunnels and diffract around hills. Long-wave radio waves have a wavelength between 1 km and 10 km. Long-wave radio waves are able to be received even if the receiver isn’t in the line of site of the transmitter; this is because the long-wave radio waves will diffract. A diagram showing long-wave radio waves being diffracted is shown below.
Short-wave radio waves can be received at long distances from the transmitter. This is because the waves are reflected from the ionosphere. The ionosphere is an electrically charged layer of the earth’s upper atmosphere. The diagram below shows how short-wave radio waves are reflected from the ionosphere.
Medium-wave radio waves can sometimes be reflected from the ionosphere depending on the time of day and the atmospheric conditions.
Very short-wave radio waves send signals over very short distances. Examples are Bluetooth and wifi. With very short-wave radio waves, you need to be in direct sight of the transmitter.
TV and FM radio also have very short wavelengths. To receive the waves from TV and FM radio, you must be in direct site of the transmitter as the short-wave radio waves will not diffract around hills and will not travel far through buildings.