Electromagnetic waves levels 7-9

Question 1

Explain what an electromagnetic wave is made of

How does this account for their ability to travel through a vacuum?

Answer 1

An electromagnetic wave is made up of oscillaitons in electric and magnetic fields. The oscillations are at 90˚ to each other.

The waves can travel through a vacuum as they do not require an particles to pass on the vibrations, as they are instead made up of vibrating fields.

Question 2

Explain why electromagnetic waves with a shorter wavelength always have a higher frequency

For example: compare the frequencies of red light (750nm) and violet light (400nm)

Answer 2

The wavelength and frequency of a wave are linked by this equation:

Speed = frequency x wavelength

All electromagnetic waves travel at the same speed in a vacuum, this is 3x10⁸ m/s. As the speed is constant if the wavelength increases the freqency must reduce to keep the speed the same:

Example: Frequency of red light

frequency = speed/wavelength

= 3 x 10⁸/750 x 10^-9

= 4 x 10¹⁴ Hz

Violet light

frequency = 3 x 10⁸/400 x 10^-9

= 7.5 x 10¹⁴ Hz

This shows that violet light has a higher frequency than red light.

Question 3

Explain how to determine the wavlength of radio waves in air.

Answer 3

1. Set up a radio wave transmitter opposite a relflective screen
2. fire the radio waves at a screen so that they reflect back, this will create a standing wave where the peaks seem to stay in the same place.
3. Move the reciever until it picks up the maximum intensity of radio waves, this is the first peak (canned an antinode in a standing wave)
4. move the reciever until you pick up the next antinode
5. As antinodes are half a wavelength apart, you can double this value to find the wavelength of the wave.

Question 4

Explain how a radio works

Answer 4

1. An oscillator will generate a carrier wave. This is a radio wave with a constant frequency
2. A sound wave is added to the carrier wave. This is called modulation. If the sound wave is added in a way that changes the amplitude of the carrier wave, it is called amplitude modulation (AM). If the sound wave is added in suca a way that it changes the frequency of the carrier wave, it is called frequency modulation (FM)
3. The modulated carrier wave is sent into the atmosphere by the transmitter arial.
4. When the radio wave hits the recieve arial, it causes the electrons in the arial to vibrate. This generates an electric current
5. The electric current is detected by the reciever. The carrier wave is removed to leave the original sound wave, which is then played out of the speakers.