EM uses

• radio waves:

  • used for communication e.g television or radio
  • easily transmitted through air
  • do not cause damage to human body
  • long wave radio transmitted and recieved around world
  • wavelength diffracts round curved surface of Earth
  • short wave radio recieved at long distances from transmitter
  • reflected from ionosphere
• how are radio waves produced?

  • produced by oscillations in electrical circuits
  • radio waves absorbed by conductor and transfer energy to electrons in reciever
  • energy causes electrons to oscillate and generate alternating current
  • current has same frequency
• microwaves: cooking food

  • high frequency microwaves have frequiences which are easily absorbed by molecules in food
  • internal energy increases so causes heating
  • water molecules transfer energy to rest of molecules in food by heating
• microwaves: satellites

  • easily to use microwaves because they pass easily through Earth's atmosphere
  • signal from transmitter is transmitted to space
  • recieved by satellite in space
  • satellite transmits signal back to Earth and recieved by satellite dish
• infrared:

  • used in electrical heaters , cookers, infrared cameras
  • infrared has frequencies absorbed by some chemical bonds
  • internal energy of bonds increases
  • causes heating - cooking food, heaters
  • all objects emit infrared
  • infrared cameras create electrical signal and displayed as picture
• visible light:

  • used in fibre optic communications
  • carry data e.g telephones
  • work by reflection
  • light rays bounced back and forth
  • light is not easily scattered and absorbed as it travels along fibre
  • cladding to protect fibre
• ultraviolet:

  • can cause skin to tan or burn
  • fluorescent light absorbs UV and emits visible light by layer of phosphor
  • are energy efficient - used for long periods
  • used in security pens, ink seen under UV light
• x-rays:

  • x-rays and gamma transmitted through tissue with little absorption
  • useful for internal imaging
  • x-rays absorbed by dense material like bones
  • used for x-ray image
  • high doses of x-rays used to kill all living cells
  • treat people with cancer
• gamma rays:

  • used as medical tracer
  • weakly ionising so can pass out body to be detected
  • can be harmful so radiographers wear lead aprons or stand behind lead screens
  • can cause mutation of genes, can lead to cancer
• • ultraviolet waves can cause skin to age prematurely and increase risk of skin cancer
• • x-rays and gamma rays are forms of ionising radiation
  • knock electrons off of atoms
  • cause gene mutation, lead to cancer
• radiation dose:

  • maesure of risk of harm caused by exposing body to ionising radiation
  • background radiation comes from:
  • radioactive rocks in Earth's crust
  • cosmic rays from space
  • man made sources like nuclear accidents