electromagnetic waves

• • There're SEVEN types of ELECTROMAGNETIC WAVES that form a CONTINUOUS SPECTRUM which groups each type in terms of their WAVELENGTH and their FREQUENCY.
  • The RADIO WAVES have the HIGHEST WAVELENGTH and LOWEST FREQUENCY, and the GAMMA RAYS have the LOWEST WAVELENGTH and the HIGHEST FREQUENCY.

  A) high

  B) low

  C) low

  D) high

  E) radio

  F) gamma

  
• How radio waves are transmitted and received:

  In the transmitting Antenna:

  • The ELECTRONS move up and down due to the AC, creating radio waves that radiate away from the antenna.
  • These radio waves can travel long distances and be RECEIVED by another antenna (receiver) tuned to the same frequency.

  A) radio waves

  
• How radio waves are transmitted and received:

  In the receiving antenna:

  • The metal aerial ABSORBS the incoming radio waves.
  • As the radio waves pass through the receiving antenna, they cause ELECTRONS to VIBRATE and create an ALTERNATING CURRENT in the circuit connected to it.
  • This AC has the SAME FREQUENCY as the radio waves.
  • This induced current can then be converted back into sound or other forms of data by the receiver's electronics.

  A) transmitter

  B) receiver

  
• Microwaves


  Created by an alternating current in an aerial coupled with a magnetron (it converts electrical and magnetic currents into a very powerful form of heat):

  • used for SATELLITE COMMUNICATIONS in space because they can travel through the Earth's atmosphere.
  • Used in cooking, it excite water molecules in food, heating it quickly and efficiently - Meaning microwaves can cause skin burns.
  • used in radar and communication through mobile phones.
  • used in communication as data is transmitted by phones.
  • Used in wifi
  • Used in GPS trackers

  Only harmful in high quantities.

  
• Visible Light

  • Used in cameras, monitor screens and FIBRE OPTIC COMMUNICATIONS, as it can carry large amounts of data over long distances with very little loss of signal.
  • used in communications like in mobile phones.
  • Used in bar code readers
  • Used in safety clothing
  • Cells in the eyes are adapted to detecting visible light, so it's used for imaging.
  • The human eye only detects the visible spectrum (7x10^-7 --> 4x10^-7m wavelength)

  
• Atomic and Nuclear Changes:

  At the atomic level, changes in atoms and their nuclei can lead to the EMISSION or ABSORPTION of electromagnetic waves across a broad frequency range.

  A) absorb

  B) higher

  C) emits

  D) lower

  
• Atomic and nuclear changes:

  • When an electron ABSORBS ELECTROMAGNETIC RADIATION, it MOVES to a HIGHER energy level FURTHER from the nucleus.
  • When an electron EMITS ELECTROMAGNETIC RADIATION, it MOVES to a LOWER energy level CLOSER to the nucleus.
  • This is how GAMMA RAYS are produced from changes in the nucleus of an atom.

  
• SIEVERTS (Sv)


  Measures the risk of HARM from RADIATION exposure.
• X-RAYS and GAMMA RAYS 

  • Both rays have enough energy to remove electrons from atoms, causing become ions, called ionising.
  • If this ionising radiation happens in living cells it can damage cells and mutation in the DNA, increasing the risk of CANCER.
• The order of the electromagnetic spectrum:

  1. Radio waves
  2. Microwaves
  3. Infrared
  4. Visible Light
  5. Ultraviolet
  6. x-rays
  7. gamma rays
• Waves that are ionising radiation

  • ultraviolet rays
  • x-rays
  • gamma rays
• EM waves can be absorbed or produced by changes inside an atom or nucleus.

  Gamma rays are produced by changes in the nucleus of an atom.
• Radiation dose (in Sieverts)


  The risk of harm from exposure of the body to a particular radiation.
• Electromagnetic waves are made up of oscillating electric and magnetic fields.

  • It's generated by using electricity in the form of alternating current as AC are made up of oscillating charges.
• Infrared cameras are able to show the parts of the hand are at different temperatures, because different temperatures emit different intensities of infrared radiation, which are represented as different colours.

  
• it's much less than 100mSv

  
• radio waves reaching a car aerial produce signals in the electrical circuit of the car radio by:

  • The car aerial absorbs radio wave and makes the electrons vibrate, which creates an alternating current and the frequency is the same.
• specular reflection


  occurs on surfaces, where the boundary is flat (e.g. a mirror)

  • all the normals are in the same direction
  • all the incoming light rays are reflected in the same direction, which will produce a clear image
  • Light reflection always follows the LAW OF REFLECTION

  
• Different wavelengths are refracted by different amounts.

  
• gamma rays can come from radioactive decay.

  
• visible light, ultra-violet and x-rays can come from, when electrons drop down energy levels.

  
• infrared rays can come from when bonds holding molecules together, vibrates.

  
• • once EM waves has been emitted, they can travel the universe, through empty space.
  • when it comes into contact with something, it can either be reflected, absorbed, transmitted or even combination of these.

  (e.g. some waves are reflected, but other waves are absorbed)

  
• X-rays are abled to produce an image of bones as:

  • X-rays are emitted through the tube.
  • Thick or hard objects absorb x-rays passing through them, so they appear lighter on the film.
  • Soft tissues transmit through them, so they appear dark.
  • The transmitted x-rays are detected.

  X-rays are able to produce detailed images, because their wavelength is very small.

  
• electromagnetic waves:

  • All are transverse waves that transfer energy from the source to the absorber.
  • When Travelling through a vacuum, all electromagnetic waves travel at the same speed (3x10^8 m/s) which is the the speed of light.
  • In different mediums they travel at different speeds; e.g refraction.

  
• Infrared radiation



  Emitted from all objects that have thermal energy, (depending on the object's temp.)

  The hotter the object, the more infrared radiation it will emit:

  • Used in ELECTRICAL HEATERS.
  • used in cooking
  • used for thermal imaging like in INFRARED CAMERAS to detect heat, which is useful in night-vision devices.
  • used in communication - remote controls / fibre optic communications.
  • Used for infrared cameras in medicine for heat therapy or to check for unhealthy tissues
  • Used for spectroscopy

  
• Infrared radiation (IR)


  Used in cooking (ovens, grills, toasters).

  • By heating the metal inside, so it can emit lots of infrared radiation to heat out food by transferring the heat energy.
  • Doesn't penetrate the surface:
  • E.g. how bread gets toasted in a toaster, instead of just getting warmer, like microwaves
  • Only harmful in high quantities.

  
• • Some frequencies of microwaves can be absorbed by water molecules, so it can be used for microwave ovens. etc.
  • Other frequencies of microwaves cannot be absorbed by water molecules, so it can be used for satellite communications. etc.

  
• visible light


  Used in communications by optical fibres (thin glass or plastic fibres):

  • able to transmit pulses of light over long distances:
  • the light is reflected when it hits the surface.
  • it ends up bouncing back and forth, throughout the entire journey.
  • until it emerges at the other end of the fibre, where it can be interpreted.
  • by encoding information into the light pulses, it can transmit data quickly over long distances.
  • but have to be materials that will reflect the light (than absorbing).
  • To ensure the reflection is specular (than diffuse) so the light isn't scattered at all.

  
• Alternatives of optical fibres are:

  • copper wires
  • electricity

  but optical fibres can:

  • transmit much more info
  • signals are less likely to be distorted (during transmission)

  
• Ultraviolet/UV rays:

  • Used in fluorescence, ENERGY-EFFICIENT LAMPS, where UV light is converted into visible light.
  • used in security to check for "invisible markings" on passports / bank notes.
  • It destroys microorganisms in water sterilisation.
  • Used in TANNING BEDS for artificial tans.
  • Crime scene investigations
  • Killing germs in hospitals.

  The sun emits ultraviolet radiation to give:

  • Sun tans
  • Sun burns

  
• Ultraviolet rays:

  Used in the property of Fluorescence, Where UV light is absorbed and the energy is re-emitted as visible light.

  Uses of fluorescence:

  • Fluorescent paints
  • Fluorescent lights:
  • generates UV radiation, which is absorbed by a layer of phosphorus (coats the inside of the glass bulb).
  • The phosphorus re-emits the energy as visible light.
  • This is energy efficient to save electricity bills and carbon dioxide emissions.

  
• Ultraviolet radiation can cause:

  • ageing of the skins
  • sunburn
  • skin cancer
  • blindness
• Gamma rays


  • used to sterilize medical instruments and food, so it kills bacteria.
  • it can kill microorganisms without causing any other damage.
  • used in cancer treatment like radiotherapy to target and kill cancer cells.
  • Used to perform medical imaging

  
• Putting a beaker of water in a microwave and turning it on for a min or 2 will increase the temperature of the water.

  An experiment to investigate the relationship between the time the microwave is on and the increase in temperature of water in a beaker:

  • pour 100ml of water into a beaker.
  • measure the temperature of the water in the beaker.
  • Put it in the microwave for 30secs.
  • Take the beaker of water out and measure the temperature after.
  • Repeat the process, but when putting it in the microwave, do it up to 2 mins to get a range.
  • Plot a graph to find the relationship.
• Radio waves:


  Created using an ALTERNATING CURRENT (AC) in a circuit connected to an antenna. The AC causes ELECTRONS to OSCILLATE, which then generates radio waves with the same FREQUENCY as the AC.

  • Used in wireless communication, such a TV and radio.
  • Connects wireless printers or computer mouse.
  • Used in blue-tooth enabled devices
• Describe how radio waves are different from sound waves:

  Radio waves:

  • transverse waves
  • travel in a vacuum
  • part of the electromagnetic spectrum
  • travel at a higher speed
  • has greater frequency
• Properties of infrared and microwaves that are the same:

  • both are transverse waves
  • both can travel through a vacuum space
  • same speed
  • can be:
  • refracted
  • reflected
  • diffracted
  • absorbed
  • transmitted
  • both transfer energy
• X-rays:


  Used:

  • for MEDICAL IMAGING (X-ray radiography) to view the internal structure of the body.
  • In airport security
  • In industries to check cracks in metals, aircraft wings and nuclear reactors. etc.
  • To detect bone fracture
  • detect dental problems
  • killing cancer cells
  • CT scanning

  The wavelength is about the same as the diameter of an atom.
• radio waves:

  • are transverse
  • travel at a higher speed
  • don't need a medium
  • are electromagnetic while sound waves are mechanical