ANS PP Chapter 13 Notes

13 - 1 Chapter 13 Electromagnetic Waves Pure Physics Notes Chapter 13: Electromagnetic Wave 13.1 What Are Electromagnetic Wave ? In this chapter, we will learn that continuous electromagnetic wave spectrum covers a large range of wavelengths and frequencies. Type of Wave: Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-Rays, Gamma rays The following lists some facts about electromagnetic waves: 1. All electromagnetic waves are transverse wave. 2. Electromagnetic waves are made up of oscillating electric and magnetic fields (Figure 3.1). They do not carry electric charges. Figure 13.1 Electromagnetic wave with oscillating electric and magnetic fields 3. All electromagnetic waves can travel without a medium, with the same speed of 3 x 108 m/s in a vacuum. 4. The wave speed equation, v = fλ, applies to all electromagnetic waves. 5. When an electromagnetic wave travels from a vacuum to other media, the wave speed and wavelength decreases. The decrease in speed is different for different frequencies. However the frequencies stays the same as at the source when the wave goes into a different medium. 6. Electromagnetic waves undergo reflections and refractions. 7. Ionising waves are those with higher frequencies and hence higher energies. They can eject electrons from atoms and molecules to create ions. The ions can cause harm by disrupting cell functions and even killing them. 8. All materials body emit range of electromagnetic waves. In general, higher temperature bodies tend to emit more and higher frequency electromagnetic waves.

13 - 2 Chapter 13 Electromagnetic Waves Pure Physics Notes Quick Check 1: 1. (a) Describe the direction of oscillation of electromagnetic waves with respect to their direction of travel. The oscillation are perpendicular to the direction of travel. (b) State what happens to the speed, wavelength and frequency of electromagnetic waves when they travel from a vacuum to a material such as glass. The speed and wavelength are reduced while the frequency is unchanged. 2. Arrange the following types of electromagnetic waves in order of increasing frequency. Radio waves Microwaves Infrared Visible Light Ultraviolet X-rays Gamma Rays 13.2 What Are The Uses And Dangers Of Electromagnetic Waves ? Uses of Electromagnetic Waves 1. Radio waves When you tune in to a radio station, sound is transmitted through the air to your radio set via radio waves. Information in radio waves can be transmitted by two methods. The first is called amplitude modulation (AM) as information is conveyed by varying the wave amplitude. The second is called frequency modulation (FM) as information is conveyed by varying the frequency. 2. Microwaves Microwaves are used very extensively for communication. The best-known example is in mobile phone communication where many tran