Wave Optics Mind Map

Huygens' principle states that every point on a wavefront acts as a source of secondary wavelets, and the common tangent or envelope to these wavelets gives the position of the new wavefront after a short time.

When drawing the construction, show the original wavefront, secondary wavelets, the forward envelope and rays perpendicular to the wavefront. Label the time interval and wave speed if a derivation is involved.

Refraction by Huygens' principle explains the bending of a plane wavefront at a boundary because light travels with different speeds in two media, leading to the relation n1 sin theta1 = n2 sin theta2.

In derivations, clearly mention that v1 and v2 are the speeds in the two media and use n = c/v to convert the speed relation into Snell's law.

Young's double-slit experiment demonstrates interference of light using two coherent sources, producing alternate bright and dark fringes on a screen. The fringe width is beta = lambda D/d.

Always convert nanometres to metres and centimetres or millimetres to metres before substitution. State whether the point is bright or dark by checking path difference.

Single-slit diffraction is the spreading of light after it passes through a narrow slit, producing a broad central maximum and weaker secondary maxima. Minima occur at a sin theta = n lambda for n = 1, 2, 3, ...

Mention that diffraction is more prominent when slit width is small and comparable to wavelength. Compare it with interference only when asked; do not mix slit separation d with slit width a.

Polarisation is the restriction of light vibrations to one plane perpendicular to the direction of propagation. It proves that light waves are transverse.

In Malus's law, theta is the angle between the transmission axes of the polariser and analyser, not the angle of incidence. For Brewster's law, tan theta_B = n is used for light incident from air into the medium.