Question

Define wavefront. Use huygens' principle to verify the laws of refraction. (b) how is linearly polarised light obtained by the process of scattering of light ? Find the brewster angle for air glass interface, when the refractive index of glass = 1.5.

Answer 1

Wavefront - It is locus of all points having same phase at given point in time.

Refer to attached diagram,

Q is the point on wavefront PA.

t = QK/c + KQ'/c  ... (1)

In Δ AQK (right angled triangle)

∠QAK = i

∴ QK = KA sin i

Similarly, in ΔQ'P'K,

KQ' = KP' sin r ... (2)

From (1) & (2), we get

t = AK sin i/c + KP' sin r/c

Now, KP' = AP' - AK

t = [ AP' sin r + AK  (sin i - sin r)] / c

Different point of incident wavefront will take same time to reach points on reflected wavefront. So t is independent of AK.

AK  (sin i - sin r) = 0

hence i = r

b) μ = tan p

μ - Reflective Index

p = Polarizing Angle

μ = 1.5

tan p = 1.5

p = 56.31°