CBSE Class 12 · 2020 · Wave OpticsShort Answer

WhatsApp Email

Define the wavefront of a travelling wave. Using Huygens' principle, obtain the law of refraction at a plane interface when light passes from a denser to a rarer medium.

Solution

Wavefront:

the continuous locus of all points of a medium that are vibrating in the same phase at a given instant.

Law of refraction (denser to rarer):

a plane wavefront incident at angle

i

has its end

B

travel

B C = v_{1} t

to reach the interface, while a secondary wavelet from the other end spreads

A E = v_{2} t

into the rarer medium. The refracted wavefront makes angle

r

sin i = \frac{B C}{A C} = \frac{v _{1} t}{A C}, sin r = \frac{A E}{A C} = \frac{v _{2} t}{A C}

∴ \frac{sin i}{sin r} = \frac{v _{1}}{v _{2}} = constant

\frac{sin i}{sin r} = \frac{v _{1}}{v _{2}}

Since

v_{2} > v_{1}

, the ray bends away from the normal, consistent with denser-to-rarer refraction.

CBSE Class 12 Board · 2020 · Subjective

Practise more: all CBSE board PYQs on Wave Optics →

CBSE Class 12 · 2020 · Wave OpticsShort Answer

Solution

More board questions on Wave Optics