## Working with Spectroscopy

### Higher Education Authority

Physics
This lesson deals with the function of spectroscopy. It describes the electromagnetic spectrum and explains the relationship between wavelength and frequency. It also covers the concept of the photon and the spectrum of hydrogen. Some applications of spectroscopy are described.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

### Lesson excerpt

The mysteries of light
Light has always intrigued scientists. Interest really exploded when Newton discovered that visible ‘white’ light is composed of a series of coloured lights. He used a prism to split white light into its constituent colours and another prism to recombine the colours as white light. He published his major work on light called Opticks in 1704. His theory of ‘particles’ was generally accepted until the wave theory of light emerged.

Many famous experimental and theoretical scientists have contributed to the process leading to our current level of understanding of light as a form of electromagnetic radiation. Such scientists include Maxwell, Hertz, Bohr, Michelson and Einstein. We now know that light behaves like straight line rays and also like waves. It also behaves like particles, which we now callphotons.

What is the electromagnetic spectrum?
Light is not the only form of electromagnetic radiation. The total range of electromagnetic radiation is called theelectromagnetic spectrum. The spectrum is usually divided into seven sections. This is shown below along with the constituent colours of visible light.

Radio waves have the longest wavelengths (105 – 10-3 metres) while gamma rays are the shortest (10-11 – 10-14 metres).

The term electromagnetic derives from the fact that the wave is a result of changing electric and magnetic fields. Allelectromagnetic radiations travel in a vacuum at the same speed, generally referred to as the speed of light.

### True or False?

1. Violet light has a longer wavelength than yellow light false
2. The electromagnetic spectrum is broadly divided into seven sections true
3. Visible light is the only form of electromagnetic radiation false
4. X-rays have a higher frequency than microwaves true
5. The components of white light in order of appearance in the spectrum are red, orange, blue, yellow, green, indigo, violet false
6. All electromagnetic radiation travels at the speed off light true
7. A photon is a particle that weighs less than a nanogram true
8. In the formula e=hf, f is called Planck's constant false
9. You can derive the wavelength if you know the frequency and the speed of light true
10. The lowest level of energy that an electron can occupy is called the ground state. true
11. The instrument used to measure and detect spectra is usually called a voltmeter false
12. Spectroscopy can be used to measure atmospheric pollution true