waves

• longitudinal waves

  • direction of oscillation is parallel to direction of energy transfer
  • sound waves
  • consists of compressions and rarefactions
• transverse waves

  • direction of oscillation is perpendicular to direction of energy transfer
  • water, light, electromagnetic waves
• wavelength

  • length of one complete wave
• time period

  time taken for one wave to pass
• frequency

  • number of waves passing every second
  • 1/time period
• wave equation

  wave speed = frequency x wavelength
• waves practical aim

  calculate wave speed by measuring frequency and wavelength
• wave practical variables

  independent - frequency

  dependent - wavelength
• wave practical steps - ripple tank

  • project image of ripple tank onto paper/screen
  • measure the length of 10 complete waves
  • divide by 10 to get wavelength
  • repeat for different frequencies
• wave practical steps - stationary wave on string

  1. use oscillator, bench pulley and slotted masses
  2. change frequency until the simplest stationary wave is formed on the string (one loop)
  3. vary frequency and move oscillator to repeat
• electromagnetic spectrum

  • radio waves - phones, tv, wifi
  • microwaves - cooking absorbed by water
  • infra-red - cooking absorbed by surface
  • visible light - vision
  • ultraviolet - tanning
  • x-rays - medical scans
  • gamma rays - sterilising, medical treatments
• how are em waves made

  • emmited when electrons loose energy
  • if energy is high enough it can cause an electron to leave its atom leaving an ion
  • uv, x-rays and gamma are ionising radiation
• infrared radiation practical - emmision

  • fill a Leslie cube with hot water from a kettle
  • use an IR detector/thermometer to measure relative emission of IR from different surfaces
  • use a ruler to ensure the distance is the same every time
• infrared radiation practical - absorbtion

  • put thermometer and bung in test tube with different materials wrapped around
  • place at same distance from IR lamp
  • matte black is the best absorber and emmiter
  • shiny surfaces are the worst
• what is refraction

  when waves enter a new medium their speed and angle changes
• permanent vs induced magnets

  permanent - always produce a magnetic field

  induced - become magnetised when in another magnetic field
• mini compasses or iron fillings

  • put in a magnetic field to visualise it
  • draw the field lines from north pole to south pole
• iron cobalt and nickel

  • magnetic and can become induced magnets
  • are attracted to permanent magnets
  • metals like aluminium and copper are not
• what is the motor effect

  a current carrying wire in a magnetic field will experience a force as it produces its own magnetic field that interacts with the other
• flemings left hand rule

  • gives direction of force
  • force is force
  • first finger is field
  • second finger is current
• refraction practical aim

  calculate refractive index or a material
• refraction practical variables

  independent - angle of incidence

  dependent - angle of refraction

  control - ray box, material of block
• refraction practical steps

  • Place glass/perspex block on a piece of paper
  • Shine light from a ray box in at an angle.
  • Draw around the block, and mark the point of origin of the ray, as well as its entry and exit points, and the normal (90° to surface).
  • Measure the angle of incidence (i) and angle of refraction (r) from the normal (0° of the protractor on the normal).
  • Repeat for varying angles of incidence, calculate refractive index for each repeat (you can also calculate a mean of these).