Electromagnetic spectrum

There are 7 types of electromagnetic waves which form the electromagnetic spectrum (EMS).

Radio waves have long wavelengths, low frequency & low energy. Gamma rays have short wavelengths, high frequency & high energy.

All electromagnetic waves travel at the same high speed in a vacuum. The speed of electromagnetic waves in a vacuum is 3.0 × 108m/s and is approximately the same in air.

Uses:

• Radio waves — radio and television transmissions, astronomy, radio frequency identification (RFID).
• Microwaves — satellite television, mobile phones (cell phones), microwave ovens.
• Infrared — electric grills, short range communications (such as remote controllers for televisions), intruder alarms, thermal imaging, optical fibres.
• Visible light — vision, photography, illumination.
• Ultraviolet — security marking, detecting fake bank notes, sterilising water.
• X-rays — medical scanning, security scanners.
• Gamma rays — sterilising food and medical equipment, detection of cancer and its treatment.

Harmful effects from excessive exposure:

• Microwaves — internal heating of body cells.
• Infrared — skin burns.
• Ultraviolet — damage to surface cells and eyes, leading to skin cancer and eye conditions.
• X-rays & gamma rays — mutation or damage to cells in the body.

The higher the frequency, the higher the energy of the radiation. Radiation with higher energy is:

• Highly ionising.
• Harmful to cells and tissues causing cancer.

Communication with artificial satellites

Communication with artificial satellites is mainly by microwaves:

• Some satellite phones use low orbit artificial satellites
• Some satellite phones and direct broadcast satellite television use geostationary satellites

Many important systems of communications rely on electromagnetic radiation including:

• Mobile phones (cell phones) and wireless internet use microwaves because microwaves can penetrate some walls and only require a short aerial for transmission and reception.
• Bluetooth uses low energy radio waves or microwaves because they can pass through walls, but the signal gets weakened.
• Optical fibres (visible light or infrared) are used for cable television and high-speed broadband because glass is transparent to visible light and some infrared; visible light and short wavelength infrared can carry high rates of data.

Sound signals

Sound can be transmitted as a digital or analogue signal:

Benefits of digital signalling:

• Increased rate of transmission of data.
• Increased range due to accurate signal regeneration.