electromagnetic waves

• What type of waves are electromagnetic waves?

  Transverse waves
• How do infrared waves transfer energy?

  From a hot object to an absorber
• What can different substances do with electromagnetic waves?

  Absorb, transmit, refract, or reflect them
• What causes refraction of electromagnetic waves?

  Difference in wave velocity in substances
• How are electromagnetic waves grouped?

  By their wavelengths and frequencies
• What is the speed of electromagnetic waves in a vacuum?

  $3 \times 10^8 \text{ m/s}$
• What is the wavelength range for long wavelength electromagnetic waves?

  10000+ nm
• What are the types of electromagnetic waves in order of wavelength?

  Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
• How are gamma rays produced?

  By changes in the nucleus of an atom
• What happens when electrons in an atom move down energy levels?

  They emit electromagnetic waves
• How are radio waves produced?

  By oscillations in an electrical circuit
• What occurs when radio waves are absorbed by a receiver aerial?

  They create an alternating current
• What is the risk associated with exposure to some electromagnetic waves?

  They can have hazardous effects
• What is radiation dose measured in?

  Sieverts
• What are the uses and hazards of radio waves?

  Uses:

  • Television and radio signals
  • Can travel long distances
  • Longer wavelengths bend around obstructions

  
  

  Hazards:

  • Can penetrate the body and cause internal heating
• What are the uses and hazards of microwaves?

  Uses:

  • Satellite communications
  • Cooking food
  • Can pass through Earth's atmosphere

  
  

  Hazards:

  • Can penetrate the body and cause internal heating
• What are the uses and hazards of infrared waves?

  Uses:

  • Electrical heaters
  • Cooking food
  • Cameras detect emitted infrared waves

  
  

  Hazards:

  • Can damage or kill skin cells due to heating
• What are the uses and hazards of visible light?

  Uses:

  • Fibre optic communications
  • Short wavelength carries more information

  
  

  Hazards:

  • Can damage the retina
• What are the uses and hazards of ultraviolet waves?

  Uses:

  • Energy efficient lights
  • Artificial sun tanning

  
  

  Hazards:

  • Can damage skin cells and cause cancer
  • Can cause blindness
• What are the uses and hazards of x-rays and gamma rays?

  Uses:

  • Medical imaging and treatments
  • Pass easily through flesh

  
  

  Hazards:

  • Can damage or kill cells
  • Can cause mutations and lead to cancers
• What do ray diagrams illustrate about refraction?

  They show how waves change direction at boundaries
• What happens to a refracted ray if it slows down crossing a boundary?

  It bends towards the normal
• What happens to a refracted ray if it speeds up crossing a boundary?

  It bends away from the normal
• What occurs if a wave travels along the normal at a boundary?

  It changes speed but not direction
• What is a wave front in wave front diagrams?

  An imaginary line at right angles to the wave direction
• What happens to wave fronts if a wave slows down at a boundary?

  They become closer together
• What occurs when a wave crosses a boundary at an angle?

  One end changes speed before the other