Waves

• Transverse waves have oscillations perpendicular to the direction of energy transfer
• EM waves are transverse waves
• Longitudinal waves have oscillations parallel to the direction of energy transfer
• transverse waves have peaks and troughs
• Longitudinal waves have compressions and refractions
• Sound waves are longitudinal waves
• Only transverse waves can be polarised
• Progressive waves are waves whose oscillations travel and transfer energy
• Polarisation is?

  the restriction of a wave so all the oscillations are in a single plane.
• Polarisation is used in radio signals, polarised sunglasses and reducing glare in cameras
• Why must you ensure that the aerial and waves are in the same plane?

  as Tv and radio signals are polarised by the direction of the rods on the transmitting aerial.
• Superposition is when two waves meet and combine to form a single wave. the total displacement at a point is equal to the sum of individual displacements.
• Constructive interference?

  when the waves are in phase with eachother and create a wave with larger amplitude.
• Destructive interference?

  when waves are in antiphase and ‘cancel‘ eachother out or create a wave with smaller amplitude.
• Antiphase?

  180° out of phase.
• Path difference (m) is the difference in lengths of two waves
• stationary waves appear to stay in the same place (strings or air in a pipe)
• Stationary waves are created by two progressive waves of the same frequency travelling in opposite directions meet and interfere/superpose.
• When there is constructive interference there are?

  anti-nodes (the waves are in phase)
• When there is destructive interference?

  the waves are out of phase and there are nodes.
• Stationary waves store energy instead of transferring
• A standing wave is generated by?

  a wave generated at one end of a string, the wave is reflected at the other end and travels back in opposing direction. The frequency and length are such that the waves meet and superpose.
• Maximum points = antinodes
• Minimum points = nodes
• Fundamental frequency = 1/ (2 x length) x square root of tension/ mass per unit length
• Tension = mass multiplied by weight
• mass per unit length = mass / length
• Frequency

  the number of waves passing through a point per second (Hz)
• Frequency = 1 / time period
• what affects fundamental frequency?

  length of string, mass of string, tension in string
• If you have a longer string…

  You have a lower frequency
• If you have a heavier string

  Lower frequency (the waves travel slower)
• If you have a looser string..

  lower frequency (travel slower)
• In strings, each particle vibrates at right angle to string
• In standing waves on strings, L is the reciprocal of wavelength
• 1st harmonic is ½ wavelength, 2L. has one antinode and two nodes
• Nth harmonic : freq = n x f Number of antinodes = n Number of nodes = n + 1
• when double slits are illuminated, the two slits act as coherent wave sources.
• Coherent?

  same frequency with constant phase difference
• Light diffracts at slits and two waves superpose, forming an interference pattern. a combination of constructive and destructive superposition occurs.