P6 specification

• describe waves as either transverse or longitudinal, defining these waves in terms of the direction of their oscillation & energy transfer and giving examples of each

  • transverse waves oscillate perpendicular (at 90°) to direction of energy transfer
  • eg: all electromagnetic waves, ripples & waves, waves on string
  • longitudinal waves oscillate parallel to the direction of energy transfer
•  Define waves as transfers of energy from one place to another, carrying information

  • waves are transfers of energy from one place to another, carrying information .........
• Define amplitude, wavelength, frequency, period and wave speed and Identify them where appropriate on diagrams

  • amplitude: maximum displacement from rest
  • wavelength: distance between same points of 2 adjacent waves
  • frequency: number of complete waves
  • period: time taken for a full cycle of wave
  • wave speed: speed at which energy is transferred
  • wave speed= frequency x wavelength

  A) amplitude

  B) wavelength

  C) wavelength

  D) trough

  E) crest

  
• State examples of methods of measuring wave speeds in different media and Identify the suitability of apparatus of measuring frequency and wavelength

  ⊹ oscilloscope

  1. set up oscilloscope so detected waves @ each mic shown as separate waves
  2. start w/ mics next to spkr then slowly move 1 away until 2 waves align & moved exactly a wavelength apart
  3. measure distance between mics = wavelength (λ)
  4. use v=fλ to find spd (v)_ freq= wtv u signal gen set to (1KHz is good)
  5. speed of sound in air ≈≈330m/s so results shld roughly agree w/ that

  
• equation for period

  T = 1/f

  • T = time
  • f = frequency
• make observations to identify the suitability of apparatus to measure the frequency, wavelength and speed of waves in a ripple tank and waves in a solid 

  ⊹ ripple tank

  1. w/ signal gen attached to dipper, u can cr8 waves waves @ set freq
  2. dim the lights, turn on lamp_ should see wave crests as shadows on screen
  3. msr dist betw 10 wavelengths, ÷ by 10= avg wavelength
  4. use v=fλ to calc spd

  • SUITABLE for msring wavelengths of moving waves or small wavelengths
  • set up is SUITABLE bc you can msr wavelength without disturbing waves
• make observations to identify the suitability of apparatus to measure the frequency, wavelength and speed of waves in a solid 

  ⊹ waves on strings

  1. adjust frequency of signal gen until a clear wave on the string

  ﹥freq depends on length of string betw pulley & transducer and masses used

  2. msr wavelength

  ﹥msr 4/5 half wavelengths & ÷ to get mean half. 2x mean= avg full wavelength

  3. v=fy to calc spd, freq= wtv signal gen is set to
• Describe what electromagnetic waves are

  • transverse waves
  • transfers energy from a source to an absorber
  • travel at the same speed through vacuum or air
  • vibrations of electric & magnetic fields, not particles
  • allows them to travel through a vacuum
  • travels at different speeds in different materials which leads to refraction
• explain how EM waves are grouped

  wavelength & frequency
• List the groups of electromagnetic waves in order of wavelength

  SHORTEST WAVELENGTH

  • radio waves
  • microwaves
  • infrared
  • visible light
  • ultra violet
  • x-rays
  • gamma rays

  LONGEST WAVELENGTH

  • really, mini, ice cream, very, ultra, x-ray, ghalib
• Explain that because our eyes only detect a limited range of electromagnetic waves, they can only detect visible light

  • our eyes can only detect visible light
• there is a large range of frequencies because EM waves are generated by a variety of changes in the atoms

  • this explains why they can absorb a range of frequencies
  • different properties = different purposes
• HT ONLY:  Explain how different wavelengths of electromagnetic radiation are reflected, refracted, absorbed or transmitted differently by different substances and types of surface

  1. ABSORBED by second material, transferring energy into material's energy store
  2. TRANSMITTED through second material- wave carries on traveling ; often lading to refraction & used in communications
  3. REFLECTED - 'sent back' away from second material; how echoes made
• refraction: waves changing direction at a boundary
• explain refraction

  • when a wave crosses a boundary, it changes speed
  • if wave travels along the normal, it will change speed but not refracted
  • if it hits boundary at an angle, it's refracted
  • wave bends to normal if it slows down, bends away if it speeds up
  • higher density of material means wave is slower
• optical density

  • measure of how quick light travels through
  • higher optical density means wave is slower
• refraction & wave properties

  • wavelength of wave changes
  • frequency stays the same
• Illustrate the refraction of a wave at the boundary between two different media by constructing ray diagrams

  1. draw boundary & normal
  2. draw incident ray (incoming ray)
  3. draw refracted ray
  4. if material is optically denser then ray will bend to normal & angle is smaller

  A) air

  B) normal

  C) refracted ray

  D) glass

  E) incident ray

  F) boundary

  
• HT ONLY: Describe what refraction is due to & illustrate this using wave front diagrams

  • wave front shows all points on a wave that are in the same position after a given number of waves
  • when wave cross boundary at angle only part of wave crosses boundary first- if it's travelling into a denser material then that part travels slower
  • by the time the whole wave front crosses the boundary, the faster part of the wave front will have traveled further than the slower
  • the difference in distance traveled by the wavy front causes the wave to refract
• Required practical activity 10: investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface. 

  ⊹ leslie cube

  1. place cube on heat proof mat
  2. boil water in kettle & fill leslie cube with water
  3. wait for cube to warm up & hold a thermometer against each face; they should be the same temperature
  4. hold infrared detector a set distance from one of the cube's faces & record IR radiation
  5. repeat for each face
  6. IR higher from black & matte than white & shiny
  7. make sure results are repeatable
• Required practical activity 10: investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.

  1. two ball bearings stuck on one side of a metal plate with candle wax; other side faced to the flame
  2. one matt black, other silver
  3. ball on black plate will fall first bc it absorbs more infrared radiation
• HT ONLY: Explain how radio waves can be produced by oscillations in electrical circuits, or absorbed by electrical circuits

  • u can make radio waves with AC in a circuit
  • object which charges (electrons) oscillate to make radio waves is called the transmitter
  • when transmitted radio waves reach a receiver, it's absorbed
  • energy carried by waves is transferred to electrons in receiver
  • energy causes electrons to oscillate & if receiver is part of circuit it makes an AC
  • this current has same frequency as radio wave
• State examples of the dangers of each group of electromagnetic radiation and discuss the effects of radiation as depending on the type of radiation and the size of the dose

  • low frequency waves can pass through tissue without it being absorbed
  • high frequency like UV transfer lots of energy & causes damage
  • UV damages surface cells, leading to sunburn and premature aging of the skin
  • X-rays & gamma cause gene mutations & cancer
• Explain that changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range
• examples of uses of each group of electromagnetic radiation, explaining why each type of electromagnetic wave is suitable

  • radio waves
  • long wave radios can diffract so can be received at long distances
  • short wave radios are reflected from the ionosphere & can also be received at long distances
  • bluetooth uses this to send data between short distances between devices
  • medium waves can also reflect from the ionosphere depending on the time of day
  • TVs have to be in direct sight of the transmitter
•  State examples of the uses of each group of electromagnetic radiation, explaining why each type of electromagnetic wave is suitable for its applications

  • microwaves
  • in microwave ovens, they're absorbed by water molecules in food which causes it to heat the water which transfer this energy to the rest of the molecules in the food
•  State examples of the uses of each group of electromagnetic radiation, explaining why each type of electromagnetic wave is suitable for its applications

  • microwaves
  • communication to & from satellites bc microwaves pass easily through earth's watery atmosphere