waves

• wave speed


  speed at which energy is transferred
• wavelength


  distance from a point on one wave to the equivalent point on the adjacent wave
• time period


  time for one complete wave to pass a point
• frequency


  number of complete waves passing a point each second
• amplitude


  maximum displacement of a point on a wave away from its undisturbed position
• transverse


  wave where oscillations are perpendicular to the direction of energy transfer
• longitudinal


  wave where oscillations are parallel to the direction of energy transfer
• compression


  part of a longitudinal wave where particles are closest ogether
• rarefaction


  part of a longitudinal wave where the particles are furthest apart
• what happens to sound waves when they change media?

  frequency is always constant, but going from gas to solid the sound waves move faster so wavelength increases
• how do ears work?


  sound waves cause the ear drum to vibrate, different frequencies cause the ear drum to vibrate differently, the vibrations are converted to electrical signals in the ear and sent to the brain
• what is an ultrasound?

  any sound above 20 kHz
• uses of ultrasounds


  prenatal scans, looking for defects in solid objects, imaging organs
• benefits of ultrasounds


  provide 3D images, non-ionising which makes them safer than x-rays
• how do ultrasounds work?

  the waves are partially reflected when they meet a boundary between two different materials
• what type of waves are P-waves?

  longitudinal
• what type of waves are S-waves

  transverse
• P-waves are faster than S-waves
• P-waves can pass through solid and liquid, but S-waves can only pass through solids
• P-waves push and pull, but S-waves shake perpendicular (side to side)
• state of the crust

  solid - both waves trave through
• state of the mantle


  solid - both waves travel through
• state of the outer core

  liquid - shadow zone is created as no S-waves travel through, and refraction of P-waves causes the shadow zone section where no P-waves are detected.
• state of the inner core

  solid - detection of P-waves between shadow zones due to refraction of waves at inner core boundary
• what is the ionosphere?

  charged layer of gas in the Earth's upper atmosphere which can reflect radio waves, and transmit microwaves so that they can reach satellites in space.
• actions an electromagnetic wave can do

  reflection, transmission, absorption
• how does a radio work?

  electrons in the transmitter oscillate back and forth, producing a radiowave which is transmitted throught the air. At the receiving aerial, since it is metal, it absorbs the radio waves, creating an alternating current with the same frequency as the transmitted wave.
• how are microwaves used in cooking?


  the frequency of the microwaves matches the natural frequency of vibration of water molecules, causing them to gain energy and heat up.
• what is an optical fibre?

  a glass wire that visible light and infa red radiation can travel along
• what are optical fibres used for?


  information can be sent along them. Infa red light is absorbed less than visible light so is often used in preference to visible light.
• how to optical fibres work?

  a light is flashed on and off at one end of the fibre and the pulses of light created are detected at the other end
• how are x-ray images produced?

  x-rays are transmitted through soft tissue but are absorbed by dense tissue, producing a shadow that falls on a photographic plate to make an image.
• advantages and disadvantages of x-rays

  quick and easy to do and are high in detail. They are ionising and it's difficult to take moving ones
• what is radiation dose?

  a measure of the damage done to a person's body by ionising radiation.
• what does radiation dose depend on?

  type of radiation, how long the body is exposed to it, enrgy per second absorbed by the body from the radiation.
• what is radiation dose measured in?

  sieverts (Sv)
• how are x-rays different to gamma rays?

  they have the same properties but x-rays are produced when electrons or other particles moving at high speeds are stopped, whereas gamma rays are produced by radioactive substances.
• what is infared radiation?

  an electromagnetic wave. it can travel through a vacuum
• what objects are good emitters?

  hot objects and those with a large surface area. Dark, matte objects
• radiation when an object is heating

  it absorbs radiation at a higher rate than it emits radiation