Waves

Waves

1. Travelling Waves

   • Continuous wave involves a succession of individual oscillation
   • Compression and rarefraction

2. Wave Characteristics

   • velocity=frequency*wavelength
   • Intensity of a wave is the power per unit area that is received by the observer.
   • A ray is the path taken by the wave energy as it travels out from the source
   • A wavefront is a surface joining neighbouring points where the oscillations are in phase with one another

3. Intensity

   • Sound Intensity is the amount of energy that a sound wave brings to a unit area every second. Units Wm^-2
   • As the distance of an observer from a point source of light increase the power received by the observer will decreases the energy spreads out over a larger area.
   • Think of sphere spreading out

4. Superposition

   • In phase when there is a zero phase difference between them
   • Destructive interference takes place when the waves are exactly out of phase

5. Polarization

   • Brewster's Law
     • Ray of light entering boundary will be reflected and refracted. Reflected partially polarized
     • Right angle refraction and reflection then totally plane polarized.
     • n=(sinXi/sinXr)=(sinXi/cosXi)=tanXi
   • A polarizer is any device that produces plane-polarized light
     • An analyser is a polarizer used to detect polarized light
   • Maul's Law
     • Preferred direction will allow a component of the light to be transmitted
   • Optically active substances
     • one that rotates the plane of polarization through it.
   • Uses
     • Stress Analysis
     • Concentration of solutions
     • LCDs
       • Liquid Crystal rotates angle to adjust brightness
     • Polarimeter is a device that measures angle of plane for a given solution

6. Reflection

   • Law of reflection: i=r
   • Perfect reflection= one direction Diffuse reflection= light leaves in all directions
   • Ray always at right angles to the wave front to show what direction light is being propagared.
   • The incident ray, reflected ray and the normal line all lie on the same plane.

7. Refraction and Critical angle

   • Refractive index is the ratio of (sini)/(sinr)=n
     • If refractive index given as a particular number and other medium not mentioned assume other medium is air.
     • Measure angle between ray and normal
     • Ray entering will be parallel to ray exiting in a parallel sided block.
     • n(glass)= n(glass)/n(air)= sin(air)/sin(glass)= V(air)/V(glass)
   • Total internal reflection can only occur on the boundary between a more dense medium and a less dense medium
     • Methods for determining refractive index experimentally
       • Ray box and measuring its position. Uncertainties in angle measurement are dependent on protractor measurements.
       • Using a travelling microscope to measure real and apparent depth and apply: n=(real depth of object)/(Apparent depth of object)

8. Diffraction

   • As the angle increases the intensity of the maxima decreases
   • Other maxima lie roughly halfway between the minima on intensity graph
     • Intensity rapidly drops from central maxima
   • Wavelength needs to be of the same order of magnitude as the aperture for diffraction to be apparent
   • All waves can be diffracted EVEN LIGHT
   • All properties stay the same
   • Huygens Fresnel explanation
   • If width of obstacle < wavelength we get semi circles

9. Two-source interference

   • Application of the principle of superposition for two coherent sources having the same amplitude
     • Coherence: Same frequency, Constant phase relationship between the two sources
   • Young's double slit experiment
     • monochromatic light or filter
     • light and dark regions are called fringes
     • Intensity remains constant
   • Path difference is the extra distance traveled by parallel waves
   • s=YD/d only applies when angle is small