by Bhaskar Department of Physics K L University

Lecture 2 (28 July) Interference

Wave Theory…. Transverse and longitudinal waves: If the particles of the medium vibrate parallel to the direction of propagation of the wave are called “Longitudinal wave” If the particles of the medium vibrate perpendicular to the direction of propagation of the wave are called “Transverse wave”

Wave Theory…. Displacement of Wave is y = a Sin ωt OR y = a Sin(ωt+δ) Where a = Amplitude, ω = Frequency (ν = 2π/ ω) δ = phase difference between two waves.  λWavelength, ν Frequency, v velocity ν = v/ λ

Phase and Path Difference Path Difference  The angular separation between two points of wave is called Phase difference. It is measured in radians or degrees.  The linear separation between two points of wave is called Path difference. It is measured in mm or cm. Phase Difference= (2π / λ) x Path Difference Path Difference= (λ / 2π) x Phase Difference

Interference Principle of superposition: This principal states that the resultant displacement of a particle of the medium accepted upon by two or more waves simultaneously is the algebraic sum of the displacements of the same particle due to individual waves, in the absence of the others. If the two displacements are in same direction, the instantaneous resultant displacement due to two waves acting together is expressed as If the two displacements are in opposite directions, the instantaneous resultant displacement due to two waves acting together is expressed as R = y 1 + y 2 R = y 1 - y 2

Interference Conditions for Interference: Coherent Constant Phase difference Constant wavelength and time period Interference of light: when two light waves superimpose, then the resultant amplitude (or Intensity) in the region of superposition is different then the amplitude (or Intensity) of individual waves. This modification in the disturbance of intensity in the region of superposition is called Interference. Constructive Interference Destructive Interference