Waves

Waves

1. Wave properties

   • Straight waves that are directed at a certain angle at a hard, flat surface will reflect off at the same angle (refraction)
   • When waves pass a boundary at which the wave speed changes, so does the wavelength and the direction if the wave approaches at an angle (refraction)
   • When waves spread out after passing through a narrow gap, they diffract. The smaller the gap and longer the wavelength, the more the waves spread out
   • When waves pass through each other, each point combines for an instant (superposition)
     • "When two waves meet, the total displacement at a point is equal to the sum of the individual displacements
     • Stationary waves, two waves that cross and forms nodes and antinodes (points of none/maximum displacement) with fixed ends

2. Measuring waves

   • Key terms
     • Displacement of a vibrating particle is the distance and direction from the equilibrium position
     • Amplitude of a wave is the maximum displacement of a vibrating particle
     • Wavelength is the least distance between two adjacent vibrating particles with the same displacement and velocity
     • The period is the time taken for one complete wave to pass a fixed point (1/f)
     • The frequency is the number of cycles of a vibrating particle per second, or the number of waves passing a point per second
     • One complete cycle of a wave is from maximum displacement to the next maximum displacement
   • The higher the frequency, the lower the wavelength
   • wave speed = frequency x wavelength
   • The phase difference between two particles of the same frequency is fraction of a cycle between the two particles

3. Waves and vibrations

   • Electromagnetic waves are oscillating electric and magnetic feilds that do not require subsatnce to travel
   • Longitudinal waves oscillate parallel to the direction of travel
   • Transverse waves oscillate perpendicular to the direction of travel
   • Polarisation
     • Only transverse waves can be polarised and are plane-polarised if they only oscillate on one plane
     • Light from a lamp or candle is un-polarised and can be polarised if it passes through a polaroid filter
       • The light is then polarised because the filter only allows oscillations on one plane
     • The intensity of unpolarised light can be controlled by it passing through 2 filters and are turned relative to each other
       • The intensity is at a minimum when the filters are at 90 degrees to each other
   • Wave and vibrations that pass through a substance are mechanical waves

4. Stationary and progressive waves

   • Distance between adjacent nodes = 0.5 x wavelength
   • Stationary formed when two progressive waves with fixed ends pass through each other
   • The simplest stationary wave is called the first harmonic (a single loop with a node at each end and antinode in the middle)
   • Stationary waves that vibrate freely do not transfer energy to the environment
   • Progressive
     • All particles vibrate at the same frequency
     • Amplitude is the same for all particles
     • phase difference is equal to 2 x the distance between particles x pi all divided by the wavelength
   • Stationary
     • All particles vibrate at the same frequency except the nodes
     • Amplitude varies from nodes to antinodes
     • Phase difference is number of nodes between the two particles multiplied by pi