P6.2 - Electromagnetic Waves

• What type of spectrum do electromagnetic waves form?

  Continuous
• Order the types of electromagnetic radiation from lowest to highest frequency.

  • Radio waves
  • Micro waves
  • Infra red
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma Rays
• How do the speeds of electromagnetic radiation differ in a vacuum and in air?

  They don't.
• What property of waves in different mediums causes refraction?

  Velocity

  Wave speed is slower in denser materials, causing refraction.
• In which direction (relative to the normal) do waves refract when entering a denser medium?

  They bend towards the normal. The angle of refraction is less than the angle of incidence.
• What type of waves can be produced by oscillations in an electrical circuit?

  Radio waves
• How do radio waves create an alternating current in a circuit?

  When radio waves are absorbed, they can induce oscillations in a circuit with the same frequency as the waves themselves.
• Where do gamma rays originate from?

  Changes in the nuclei of atoms.
• What health effects can ultraviolet waves cause?

  • Premature aging of the skin
  • Increase the risk of developing skin cancer
• What health effects can X-rays and Gamma rays cause?

  • They are ionising radiation so can cause mutations in genes.
  • They can lead to increased risk of developing various cancers.
• Give 3 practical uses for infrared radiation

  1. Electrical heaters
  2. Cooking food
  3. Infrared cameras
• Give 2 practical uses for microwave radiation

  1. Satellite communications
  2. Cooking food
• Give 2 practical uses for radio waves

  1. Television transmission
  2. Radio transmission
• What wave phenomenon is used by lenses to form an image?

  Refraction
• How does a convex lens form an image?

  Parallel rays of light are refracted and brought together at a point known as the principal focus.
• What is meant by the focal length of a lens?

  The distance from the lens to the principal focus
• What is the difference between the image produced by a convex and concave lens?

  • Convex can produce real or virtual images
  • Concave can only produce virtual images
• Why does magnification not have a unit?

  It is the ratio between image height and object height, and ratios do not require units.
• What symbol is used to represent a convex lens in a ray diagram?


  A vertical arrow with outward facing arrows to indicate the shape of the lens.

  
• What symbol is used to represent a concave lens in a ray diagram?


  A vertical line with inward facing arrows to indicate the shape of the lens.

  
• What determines the colour of visible light waves?

  Wavelength and frequency of the light waves
• What colour of visible light has the highest frequency?

  Blue
• What colour of visible light has the largest wavelength?

  Red
• What is meant by the term 'specular reflection'?


  Reflection from a smooth surface in a single direction.
• What is meant by the term 'diffuse reflection'?


  Reflection from a rough surface which causes scattering.
• How does a red colour filter work?

  Absorbs all wavelengths except red, allowing only red light to pass through.
• What determines the colour of an opaque object?

  Different objects reflect different wavelengths of light by different amounts, and the most strongly reflected wavelengths determine the colour.
• What happens to the wavelengths of light that aren't reflected by an opaque object?

  They are absorbed
• What colour does an object appear if all wavelengths are reflected by equal amounts?

  White
• What colour does an object appear if all wavelengths are absorbed?

  Black