P13 - Electromagnetic waves

• Electromagnetic waves


  Electric and magnetic disturbances that can be used to transfer energy from a source to an absorber
• Everyday devices and gadgets that use waves from different parts of the electromagnetic spectrum

  • Microwave ovens
  • Radiant heaters
• Electromagnetic waves


  • They do not transfer matter
  • The energy they transfer depends on the wavelength of the waves

  
• Parts of the electromagnetic spectrum

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays and gamma rays

  
• Visible light


  The part of the electromagnetic spectrum that the human eye can detect, with wavelengths from just below 400 nm to above 700 nm

  
• Speed of electromagnetic waves

  3.0 x 10^8 m/s (300 million m/s) through space or in a vacuum
• Calculating wavelength or frequency of electromagnetic waves


  Using the wave speed equation: v = f x λ

  
• As the wavelength decreases along the electromagnetic spectrum from radio waves to gamma rays, the energy and frequency of the waves increase

  
• Parts of the electromagnetic spectrum in order of increasing frequency

  • Radio
  • Infrared
  • X-rays and gamma rays

  
• Parts of the electromagnetic spectrum missing from the list in the previous item are: microwaves, visible light, ultraviolet

  
• When an atom or nucleus emits electromagnetic waves, it emits a packet of waves referred to as a photon
• The energy of a photon is proportional to the frequency of the emitted waves

  
• The electromagnetic spectrum is made up of (in order of decreasing wavelength and increasing frequency and energy): radio waves, microwaves, infrared radiation, visible light, ultraviolet waves, X-rays and gamma rays

  
• The human eye can only detect visible light, with wavelengths ranging from just below 400 nm to above 700 nm
• Electromagnetic waves transfer energy from a source to an absorber
• Wave speed equation


  v = f x λ
• White light


  • It has all the colours of the visible spectrum in it
  • The wavelength increases across the spectrum as you go from violet to red
• How a film camera works

  1. Light is focused by the camera lens onto light-sensitive film

  2. The film needs to be developed to see the image
• How a digital camera or mobile phone camera works

  1. Light is focused by the lens onto a sensor made up of light-sensitive pixels

  2. The image is stored electronically on a memory card
• Infrared radiation


  • All objects emit it
  • The hotter an object is, the more infrared radiation it emits
  • It is absorbed by skin and can damage, burn or kill skin cells

  
• Uses of infrared radiation

  • In optical fibres for communications
  • In remote control handsets
  • In medical infrared scanners
  • In infrared cameras
  • In electric heaters and cookers

  
• Microwaves


  • They have a shorter wavelength than radio waves
  • They can pass through the atmosphere and reach satellites
  • They can carry mobile phone signals
  • They can penetrate into food and heat it by being absorbed by water molecules

  
• Radio waves


  • They are used to carry radio, TV and mobile phone signals
  • They can be used to connect devices wirelessly, e.g. Bluetooth

  
• Microwaves and radio waves can be hazardous because they penetrate people's bodies and can heat the internal parts
• Types of electromagnetic waves used in different applications

  • Radio waves detected by TV aerial
  • Visible light emitted by TV screen
  • Microwaves used for satellite communications
  • Radio waves used for wireless computer-printer connection

  
• Remote control handsets operating in the same wavelength range as mobile phones


  It would have an effect on mobile phone users
• Emergency services use radio waves in a wavelength range that no one else is allowed to use

  
• Electromagnetic wave detected by the aerial

  Radio wave

  
• Electromagnetic wave emitted by the screen

  Visible light

  
• Electromagnetic wave used to send signals to a printer from a computer without using a cable

  Infrared radiation
• Mobile phones use electromagnetic waves in a wavelength range that includes short-wave radio waves and microwaves


  Effect on mobile phone users if remote control handsets operated in this range as well

  
• Emergency services use radio waves in a wavelength range that no one else is allowed to use


  Explanation

  
• Calculating the wavelength in air of electromagnetic waves of frequency 2400 MHz


  Speed of electromagnetic waves in air is 300 000 km/s

  
• What the metal plate does to the microwaves


  Describes the effect
• Designing a test to find out if microwaves can pass through a metal plate and a thick cardboard sheet

  Test procedure
• White light contains all the colours of the visible spectrum
• Infrared radiation


  Used for carrying signals from remote control handsets and inside optical fibres

  
• Microwaves


  Used to carry satellite TV programmes and mobile phone calls
• Radio waves


  Used for radio and TV broadcasting, radio communications, and mobile phone calls

  
• Mobile phone radiation


  Microwave radiation, and also radio waves at near-microwave frequencies