Section 3 -Waves

• Explain what is meant by a progressive wave?


  The transfer of energy between 2 points without the transfer of matter
• What happens when the amplitude of a wave is changed?

  If the amplitude of a wave is changed the energy of the wave is changed
• Speed of sound in air?

  340 m/s, when calculating a range of 340-345 is okay. A number like 250 is definitely wrong.
• Superposition?

  This is the process which occurs when 2 waves of the same type meet/overlap.
• Constructive interference?

  When two waves meet and their amplitudes add together, resulting in a wave with a larger amplitude. This is because they are in phase. Phase difference = 0.
• Coherent waves?

  Waves that have the same frequency and a constant phase difference.
•  π/180?

  Conversion of degrees to radians
• 180/ π?

  Conversion of radians to degrees
• Which statement is correct about the properties of an unpolarised electromagnetic wave as it passes through a polariser?

  The intensity of the wave is reduced
• What is the phase difference between the oscillations of the particles at P and Q?

  Zero as the particles are in the same direction so here is no phase difference. (Both at the peak of a wave)

  
• Applications of total internal reflection?

  1. Cat eyes - reflectors on the road.
  2. Periscopes - to see over obstructions
  3. Binoculars - to see with a higher magnification
  4. Optic fibers - Sending signals
• Define dispersion

  white light separating into its colour components (that have different wavelengths) as it refracts
• Nred = 1.513 and Nblue = 1.532. Which wave would be faster (N is the refractive index)


  The red wave as it has a smaller reflective index
• Does a higher refractive index move closer or further from the normal?

  It moves closer and will have a slower speed
• What is the speed of light in air?

  3x10^8
• When does total internal reflection occur?

  Total internal reflection occurs for any incident angle greater than the critical angle θc, and it can only occur when the second medium has a refractive index less than the first medium

  
• What is the critical angle?

  The angle for which the refracted ray just passes along the boundary line

  
• What angles must be drawn on your medium?

  Angles between the normal and the incident/refracted/reflected ray. Never between a ray and the surface.
• Constructive interference 


  When waves that have the same wavelength, frequency and amplitude meet in phase which sums up producing a wave of twice the amplitude. OR when S1 p - S2 p = 0 there is no path difference so this is constructive interference.
• Destructive interference 


  When the path difference is (n+1/2 lambda) destructive interference occurs.
• What is diffraction?


  When a wave encounters an obstacle (a gap) or the edges of an opening, it bends around them. This bending of a wave is called diffraction and all waves exhibit this behaviour.
• When does the most bending of a wave occur?

  Maximum diffraction occurs when the wavelength is the same as the size of the gap.
• State the path difference between light from adjacent slits when this light produces a first-order maximum on the screen

  1 wavelength (The path difference would be lambda)
• What does monochromatic Light mean

  A singular wavelength