Waves

• a transfer wave is one where the vibrations are perpendicular to the direction which the wave transfers energy
• the number of complete waves/vibrations in one second is called the frequency
• speed(m/s)=frequncy(Hz)x waverate(m)
• when they reach a surface all waves can be reflected(e/g echo), transmitted or absorbed
• when a wave enters a material and its speed chugs so does the direction
• when light enters glass it slows down, its wavelength gets smaller but the frequency stays the same
• convex lenses are converging lenses. concave lenses are diverging lenses
• image size=magnification x object size
• real image=can be produced on screen

  virtual image we can see but CAN'T be produced on screen

  magnified=image larger than object

  diminished=image smaller then object

  erect=image points same way as object
• a ray of light that goes through the centre of a lease carries on without its direction being changed
• a ray that is parallel to the axis of the lens is refracted through the principal focus
• we can see a virtual image but can't produce it on a screen because the rays of light don't cross
• in a concave lens parallel rays of light ate spread out. this is a diverging lens
• white light is a spectrum of colours. when passed through a prism red is slowed down/refracted the least. violet is slowed down/refracted the most (because of these differences in speed light splits into a spectrum)
• when white light falls on white light we assume its reflected and not absorbed, when white light falls on a black surface we assume its all absorbed and none reflected
• a red filter only transmits red light and absorbs all other colours
• if you sone red light on black white and blue

  white= reflect so would appear red

  black=absorb all light would appear black

  blue =absorbs all colours but blue would appear black
• sound waves are longitudinal waves, they need something to travel through so can't across empty space
• sound waves above 200000Hz are called ultra sound
• high pitched sound has a large frequency, low pitched sound has a large amplitude
• ultrasound can be used in medicine as a safe alternative to x-rays (not ionising) they are partly reflected every time they reach a new layer of the body so can be use to scan soft parts of the body
• ultrasound can measure the depth of water, by knowing the speed of sound in water you can work out the depth by halting how long it takes to bounce off the sea floor and back to the source
• ultrasound can be used to measure humans if you low the speed of sound through human tissue
• earthquakes create semantic waves the spread through the earth and can be detected by seismographs
• Primary (P) waves are the fastest

  secondary (S) waves are slower than p and are transverse waves

  Long (L) waves are the slowest and only travel through the crust
• P and S waves both travel through solids but S waves can't travel through liquids
• s waves can't travel through the outer core but P waves can (this tells us that the inner core is liquid)
• P waves are refracted when the reach the outer core because their speed changes. the region known as the shadow zone only receives P waves (the have been refracted from the inner core)