P1- Electromagnetic Waves

P1- Electromagnetic Waves

1. THE ELECTROMAGNETIC SPECTRUM

   • Electromagnetic radiations are electric and magnetic disturbances. They travel as waves and more energy from place to place.
   • All electromagnetic waves travel through space(a vacuum) at the same speed but they have different wavelengths and frequencies.
   • All of the waves together are called the electromagnetic spectrum. We group the waves according to their wavelength and frequency: Gamma rays have the shortest wavelength and highest frequency. Radio waves have the longest wavelength and lowest frequency.
   • The spectrum is continuous. The frequencies and wavelengths at the boundaries are approximate as the different parts of the spectrum are not precisely defined.
   • Different wavelengths of electromagnetic radiation are reflected, absorbed or transmitted differently by different substances and types of surface.
   • The higher the frequency of an electromagnetic wave the more energy it transfers.
   • Radio longest wavelength... gets shorter. Radio waves have shortest frequency gets higher...
   • All electromagnetic waves travel through space at a wave speed of 300million m/s. We can link the speed of waves to their wavelength and frequency using the equation: v= f x λ
     • v= wave speed, 300,000,00m/s. f= frequency, in Hz, λ= wavelength in m.

2. LIGHT, INFRARED, MIRCOWAVES AND RADIOWAVES

   • VISIBLE LIGHT is the part of the electromagnetic spectrum that is detected by our eyes. We see the different wavelengths within it as different colours. Visible light used for photography.
   • The wavelength increases across the spectrum from violet to red. We see a mixture of all the colours as white light.
   • Infrared radiation is given out by all objects. The hotter the object, the more IR it emits. Remote controls use IR.
   • MIRCOWAVES are used in communications. Microwave transmitters produce wavelengths that are able to pass through the atmosphere. They are used to send signals to and from satellites and within mobile phone networks.
   • RADIOWAVES transmit radio and tv programmes and carry mobile phone signals.
   • Mircowave radiation and radio waves penetrate your skin and are absorbed by body tissue. This can heat internal organs and damage the,. Infrared radiation is absorbed by skin; too much will burn your skin.

3. COMMUNICATIONS

   • An alternating voltage applied to an aerial emits radio waves with the same frequency as the alternating voltage. When the waves are received they produce the alternating current in the aerial with the same frequency as the radiation received.
   • The radio and mircowave spectrum is divided into different bands. The different bands are used for different communications purposes.
   • The shorter the wavelength of the waves the more information they carry, the shorter their range, the less they spread out.
   • Mobile phones communicate with a local mobile phone mast using wavelengths just on the border between radio waves and mircowaves. They are usually referred to as mircowaves.
   • Some scientists believe that radiation from mobile phones may affect the brain.
   • Optical fibres are very thin glass fibres. We use them to transmit signals carried by visible light and infrared radiation. The signals travel down the fibre by repeated total internal reflection.
   • Optical fibres carrying visible light or infrared are used in comminications because they carry much more information and are more secure than radio waves and mircowave transmissions.

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