11. Wave Motion

Wave Motion Progressive Waves – energy is transferred in the propagation of the wave Displacement-distance (All wave particles) Displacement-time (one particle in SHM) Both graphs can be describing longitudinal (oscillation of medium along the propagation) or transverse (oscillation of medium perpendicular to the propagation) waves. Wave Equation 1fv   Frequency is inversely proportional to wavelength  Speed of wave is constant and is affected by change in medium or temperature. Phase Difference t 2T d 2         Time lapse (Δt) out of the period, T  Distance between two points in a wave (Δd) out of the wavelength, λ Intensity of wave (determines brightness of light and loudness of sound) Intensity a point source 2Ia 2 2 PI 4r 1I r    Intensity at a point is proportional to the square of the amplitude of the wave at that point.  Intensity is the wave energy incident per unit time per unit area normal to the direction of travel of the wave.  Area incident of a point source is the area of a sphere. Polarisation Malus’ Law 2 0I I cos  since 2Ia , 0a a cos   Malus’ Law is applicable to a plane polarised light of intensity I0 and amplitude a0 passing through a polariser/polaroid.  When a completely unpolarised light passes through a polariser/polaroid, it becomes polarised with halved intensity. θ I0 a0 I a Transmission axis

Calibrated Oscilloscope Let time base setting be x s cm-1 Frequency, 1f xd Wavelength Measurement (See summary sheet for Superposition)