Electromagnetic waves

• what are electromagnetic waves

  transverse waves that transfer energy from the source of the waves to an absorber
• electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum or air
• what are waves that form the electromagnetic spectrum grouped into

  wavelength and frequency - long to short wavelength / low to high frequency
• what are the groups of electromagnetic waves on the spectrum

  • radio waves
  • microwaves
  • infrared radiation
  • visible light
  • ultraviolet
  • x-rays
  • gamma rays
• our eyes only detect visible light so detect a limited range of electromagnetic waves
• different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength
• some effects - e.g refraction - are due to the difference in velocity of the waves in different substances
• what can radio waves be produced by

  oscillations in electrical circuits
• what happens when radio waves are absorbed

  they may create an alternating current with the same frequency as the radio wave itself, so radio waves can induce oscillations in an electrical circuit themselves
• what can changes in atoms and the nuclei of atoms result in

  electromagnetic waves being generated or absorbed over a wide frequency range - gamma rays originate from changes in the nucleus of an atom
• ultraviolet, x-rays and gamma rays can have hazardous effects on human body tissue, the effects depend on the type of radiation and size of the dose - radiation dose (sieverts) is a measure of the risk of harm resulting from an exposure of the body to the radiation
• ultraviolet waves can cause skin to age prematurely and increase risk of skin cancer - x-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer
• uses of radio waves

  • television
  • radio
• uses of microwaves

  • satellite communications
  • cooking food
• uses of infrared radiation

  • electrical heaters
  • cooking food
  • infrared cameras
• uses of visible light

  • fibre optic communications
• uses of ultraviolet light

  • energy efficient lamps
  • sun tanning
• uses of x-rays and gamma rays

  • medical imaging
  • treatments
• how does a lens form an image

  by refracting light - in a convex lens, parallel rays of light are brought to a focus at the principal focus. the distance from the lens to the principal focus is called the focal length. ray diagrams are used to show the formation of images by convex and concave lenses
• the image produced by a convex lens is either real or virtual
• the image produced by a concave lens is always virtual
• equation for magnification

  image height / object height
• magnification is a ratio and has no units
• each colour within the visible light spectrum has its own narrow band of wavelength and frequency
• what is specular reflection

  reflection from a smooth surface in a single direction
• what is diffuse reflection

  when reflection from a rough surface causes scattering
• how do colour filters work

  absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour)
• what is the colour of an opaque object determined by

  which wavelengths of light are more strongly reflected - wavelengths that aren't reflected are absorbed - if all wavelengths are reflected equally the object is white, if all wavelengths are absorbed the object is black
• objects that transmit light are either transparent or translucent