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SS3: PHYSICS - 1ST TERM

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Mechanical waves are waves that require material medium for its propagation. Examples are water waves, sound waves, and waves in a rope or string. 

Electromagnetic waves are waves that do not require a material medium for its propagation. They are a combination of electric and magnetic field vibrations that exist freely in space. Mechanical and electromagnetic waves differ in their velocity, while electromagnetic waves travel at the speed of light; the mechanical wave travels at a speed much less than that of light.

Electromagnetic waves are group of waves consisting of a radio wave, microwave, infrared, visible light, ultras-violet rays, x-rays and gamma rays. 

The wavelength of electromagnetic waves ranges between (103m) for radio waves to 1012m for gamma rays. The range of wavelength within this group is called electromagnetic wave.

Radio waves

  • Have the longest wavelength and shortest frequency
  • Wavelength is between few centimeters to thousands of meters
  • They are produced when electrons move up and down in antennas of TV, radio and microwave transmitters
  • Are detected by radio and TV receivers

Uses

  • Radio waves are used in radio and TV communications, microwave, UHF and VHF waves.

Microwaves

  • Detected by receivers of radar
  • Used to transmit information
  • Detect radar or presence of enemy
  • Cooking, preservation of food

Infrared

  • Hot objects emit infrared rays
  • Can be detected by the skin, thermometer with blackened bulb and photo transistor
  • Heat from the sun

Uses

  • to dry paint in automobile industries
  • used in cooking food (cookers)
  • used to take photograph of object in the dark
  • used in remote control sensor in electronic devices

Visible Light

  • it consist of Red, Orange, yellow, Green, Blue, Indigo and Violet (ROYGBIV)
  • produced by hot objects, sun
  • it help us to see things, to take photograph of objects 
  • it can be detected by use of photographic film, photo electric cells

Ultraviolet Rays

  • the wavelength is shorter than visible light but has large frequency
  • detected by photographic film and fluorescent materials
  • produced by very hot object, welding, sun
  • it makes some material fluorescence
  • it produces vitamin D

X-Rays

  • detected by photographic film (Geiger Muller tube) 
  • used in industries for detecting cracks in metals joints
  • used in arrangement of crystals in atoms (crystallography)
  • to kill cancer cells and show broken bones
  • produced when fast electrons strike a metal target

Gamma Rays

  • has shortest wavelength and highest frequency
  • detected by photographic films Geiger Muller tube
  • used in hospitals to sterilize needles and other medical gadgets
  • to kill cancerous cells

The properties of electromagnetic waves are:

  • they are all electrical fields vibrating at right angles to the magnetic field
  • they travel through a vacuum at the speed of light (V = 3 x 108m/s)
  • they are all transverse waves and can be polarized
  • They can be reflected, refracted, diffracted, or interfere with each other.
  • they vary in frequency and wavelength
  • Obey the wave equation V = fλ

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