physics electromagnetic spectrum

• what are electromagnetic waves?

  transverse waves that transfer energy from the source of the waves to an absorber
• complete the image

  A) A

  B) B

  C) C

  D) D

  E) E

  F) F

  G) G

  
• all Electromagnetic waves travel at the same speed through air or a vacuum
• radio waves are made by oscillating charges
• electromagnetic waves form a continuous spectrum over a range of frequencies. They are grouped into seven basic types based on their wavelength and frequency
• There is such a large range of frequencies because EM waves are generated by a variety of changes in atoms and their nuclei. E.g changes in the nucleus of an atom creates gamma rays.

  This also explains why atoms can absorb a range of frequencies - each one causes a different change
• Because of their different properties, Em waves are used for different purposes
• Radio waves are made by oscillating charges
• EM waves are made up of oscillating electric and magnetic fields
• Our eyes only detect visible light and so detect only a limited range of electromagnetic waves
• different substances may absorb, transmit, reflect or refract electromagnetic waves in ways that vary with wavelength
• some effects, for example refraction are due to the difference in velocity of waves as they enter different mediums
• Alternating currents are made of oscillating charges. As the charges oscillate they produce oscillating electric and magnetic fields, i.e electromagnetic waves
• The frequency of an alternating current is equal to the frequency of its associated EM wave
• you can produce radio waves using an alternating current in an electrical circuit. The object in which electrons oscillate to create radio waves is called a transmitter
• when transmitted radio waves reach a reciever, the radio waves are absorbed
• the energy transferred by the waves is transferred to the electrons in the material of the reciever
• When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit.
• radio waves are mainly used for communication
• radio waves are used for television and radio
• microwaves are used for cooking food and satellite communication
• infrared waves are used for electrical heaters, cooking food and infrared cameras
• visible light waves are used for fibre optics communications
• gamma rays are used for cancer treatment
• ultraviolet radiation is used for tanning beds
• ultraviolet waves are used for energy efficient lamps and sun tanning
• x-rays and gamma rays are used for medical treatments and medical imaging
• ultraviolet waves, x-rays and gamma rays can all have hazardous effects
• the effects of electromagnetic waves on the body depend on the type of radiation and the size of dose
• waves with higher frequency and shorter wavelength carry more energy and are therefore more dangerous
• radiation dose is measured in sieverts and is a measure of the risk of harm from radiation
• 1000 millisieverts (mSv) = 1 sievert (Sv)
• ultraviolet waves can cause skin to age prematurely and increase the likelihood of skin cancer
• X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer
• water is very good at absorbing microwaves
• humans are made up of 70% water
• visible light is made up of 7 colours:

  • red
  • orange
  • yellow
  • green
  • blue
  • indigo
  • violet
• the wavelengths decrease from red light to violet light:

  • red 620-750nm
  • orange 590-620nm
  • yellow 570-590 nm
  • green 495-570 nm
  • blue 476-495nm
  • indigo 450-475 nm
  • violet 380-450nm
• UV has a wavelength of a ten millionth of a metre
• UV is produced by very hot objects e.g the sun