em waves

• Em waves

  transfer energy from a source to an absorber
• what colour of light has the lowest frequency and longest wave length

  red
• what colour of light has a higher frequency and shorter wave length

  violet
• from radio to gamma the frequency

  increases
• the wavelength from radio to gamma

  decreases
• EM waves dont need to travel through a medium
• all EM waves travel at the same speed in a vaccum
• what do radio waves do

  transmit radio and Tv signals
• what is a property of radio waves

  they can travel long distances before being absorbed
• radio waves can deflect off a layer of charged particles in the atmosphere
• what is significant about radio waves bouncing off ionosphere

  allows them to travel long distances around earth
• what are microwaves used for

  heating food and satellite communications
• why do microwaves heat food

  because most food contain water molecules that absorb the energy and causes the temp to increase
• microwaves can pass through the atmosphere without being reflected or refracted
• what is infrared used for

  heating and cooking in ovens and infra red cameras
• infra red is easily absorbed by the surface of an object
• visible light is used for

  communication with fibre optics
• if we transmit pulses of light down fibres then we can carry information
• why can visible light carry a lot of information

  short wavelength
• how is UV used

  energy efficient light bulbs , tanning salons
• how do energy efficient light bulbs work

  the Uv energy is absorbed by the internal surface of the bulb and converted into visible light
• What are EM waves

  transverse waves that transfer energy from the source to an absorber
• All EM waves travel at the same velocity through a vacuum or through air
• The sun emits EM radiation
• all Hot objects emit infra red radiation
• microwaves emit EM radiation
• EM with a shorter wavelength carry a higher energy
• Em waves with a shorter wavelength carry a ----- energy

  higher
• the higher the energy of an EM wave the more dangerous it is
• substances may absorb , emit , transmit , refract or reflect EM waves that vary with wave length
• refraction is due to the difference in velocity of waves in different substances
• what produces radio waves

  oscillations in electrical circuits
• radio waves can induce oscillations in an electrical current ( alternating current )
• gamma rays come from changes in the nucleus of an atom
• what waves are hazardous to humans

  x rays

  UV rays

  gamma rays
• a lens forms an image by refracting light
• in a convex lens the rays of light are brought to a focus at the principle focus
• in a convex lens the rays of light are brought to a focus at

  the principle focus
• the distance from the lens and principle focus is called the focal point
• what is a real image

  an image that's formed when the rays of light are focused