# EDEXCEL PHYSICS P1: Topic 2

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The Electromagnetic Spectrum

Visible light is made up of different colours. These colours can be seen when dispersing the light into a spectrum using a prism. The then are separated from red to violet.

How was infrared discovered?...

William Herschel discovered infrared in 1800, while investigating the temperature of the visible spectrum. He found that the hottest temperatures were beyond the red end of the spectrum, where there is no visible light, this is known as the infrared region. Infrared waves have a longer wavelength than red light.

How was ultraviolet discovered?...

Johann Ritter discovered ultraviolet in 1801, while experimenting with silver chloride used in photography. (THINK: UV has silver-y undertones, use this to remember the fact he used silver chloride).He discovered the rate of reaction was highest beyond the violet end of the spectrum. Ultrawaves have a shorter wavelength than violet light.Ultraviolet waves from the sun are harmful - they will damage skin cells and eyes. The most common form of this damage is sunburn, but long exposure can cause skin cancer. There's three types of UV waves: UV-A, UV-B and UV-C. UV-C waves have the shortest wavelength and cause the most damage.

Electromagnetic Spectrum

> All electromagnetic waves are transverse and travel at the same speed in a vacuum of 3.0 x 10^8 m/s.

> All electromagnetic waves can transfer energy

> All electromagnetic waves can be reflected, refracted and diffracted (diffraction is a phenomena when the wave comes into contact with an obstacle and has to bend around it to get past - but you don't need to know this for GCSE)

> wave speed = wavelength x frequency

All EM waves are essentially the same, but they have different wavelengths and frequencies.

In order of decreasing wavelength but INCREASING frequency, the order of the EM waves are:

radio waves, microwaves, infrared, visible light, UV, x-rays, gamma rays

(THINK: Robbie made Izzie vape under an ex-gym = Robbie Made Izzie Vape Under an eX-gym)

> Remember that the frequency increases as the wavelength decreases as the frequency basically means how many complete wavelengths pass a point per second, so obviously if the wavelength increases and becomes longer, the frequency will decrease as it will take longer for all the wavelength to pass a certain point.

Electromagnetic waves consist of an oscillating electric field combined with oscillating magnetic field. Oscillating basically means they move or swing back and forth in a regular rhythm.

> The two oscillating fields are at right angles to eachother and to the direction of wave travel, which is why the waves are transverse.

> The wavelength of an EM wave can vary from the size of a nucleus to a few km's.