P6 F) Electromagnetic Spectrum – Part 1
Electromagnetic (EM) waves are transverse waves (the oscillations are perpendicular to the direction of travel). EM waves transfer energy from a source to an absorber. EM waves are oscillating electric and magnetic fields; EM waves do not need particles to oscillate. As no particles are required, EM waves can travel through a vacuum. For example, the sun emits EM waves that travel through space (a vacuum) to earth; the sun emits waves across the whole EM spectrum.
The EM spectrum is a continuous range of wavelengths and frequencies. The EM spectrum is split into different groups based on the properties of the waves; there are 7 different groups in the EM spectrum and these groups merge to form a continuous spectrum. All EM waves travel at the same speed through a vacuum; EM waves travel at around 300 million metres per second in a vacuum (3 x 108 m/s).
The wavelengths of EM waves ranges from 104 m to 10-15 m. As all of the EM waves travel at the same speed, if the wavelengths vary, so too will the frequencies (remember; v = f x λ). Parts of the EM spectrum that have long wavelengths have low frequencies (radio waves). And, parts of the EM spectrum that have short wavelengths have high frequencies (gamma rays).
The 7 groups in the EM spectrum going from the longest wavelength to shortest (or lowest frequency to highest) are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. The EM spectrum is shown below.
Our eyes are only able to detect a small part of the EM spectrum; the visible light section. Each colour within visible light has a different wavelength and frequency. Red light has the longest wavelength and lowest frequency (out of visible light). Violet light has the shortest wavelength and highest frequency (out of visible light). White light is made up of all of the different colours in the visible light spectrum. We can separate these colours in white light by shinning white light through a glass prism. The light is refracted as it enters and leaves the glass prism. The different colours within white light have different wavelengths, which results in the different colours being refracted by different amounts. Reds, oranges and yellows are refracted the least because they have longer wavelengths. Blues and violets are refracted the most because they have shorter wavelengths. The refraction of white light through a prism is shown below.
EM waves transfer energy from a source to an absorber. I am going to go through what happens when we leave our phone outside on a sunny day. The sun emits infrared radiation and there is lots of infrared radiation on a sunny day. When your phone is left out in the sun, the phone’s screen absorbs infrared radiation from the sun, which results in energy being transferred to the thermal energy stores of the phone, thus causing the phone to become hot. For this example, the sun is the source and the phone is the absorber.