write an activity to show that angle of incidence equal to angle of emergence
Answers
The light ray is refracted out of the glass slab at the surface CD along the path GH. The angle of incidence at this surface is ∠r2. The light ray emerges out of the slab forming ∠e as angle of emergence. Hence, angle of incidence equals angle of emergence.
Answer:
Assume ABCD to be the glass plate with sides AB parallel to CD.
Let the refractive index of air and glass be n1and n2.
Consider a ray of light EF incident on surface AB of the glass slab with angle of incidence, ∠i.
The light ray is refracted into the glass slab along the path FG and towards the normal, NN’ . ∠ r1 is the angle of refraction.
The light ray is refracted out of the glass slab at the surface CD along the path GH. The angle of incidence at this surface is ∠r2.
The light ray emerges out of the slab forming ∠e as angle of emergence.
The surfaces AB and CD are parallel and FG is the transversal,
Therefore, ∠r1= ∠r1
Applying Snell’s Law at the surface AB,
sin isin r1=n2n1 .......(1)
Similarly, at surface CD, according to Snell’s Law
sin r2sin e=n1n2 .......(2)
Multiplying equation 1 and 2,
sin isin r1×sin r2sin e=n2n1×n1n2sin isin r1×sin r2sin e=1
As AB is parallel to CD, the perpendiculars to the AB and CD, NN’ and MM’ are also parallel
Therefore, alternate interior angles, r1 and r2are congruent i.e. r1 = r2
Hence,
sin isin r1×sin r1sin e=1sin isin e=1Therefore, sin i=sin eor, i=e
Hence, angle of incidence equals angle of emergence.