Question

What is the critical angle of a transparent crystal is 45 degree then its?

Answer 1

When light is travelling from a denser medium to a rarer medium and the angle of incident is equal to the critical angle, the angle of refraction is 90o.90o.

⇒sinicrsin90o=1μ,⇒sin⁡icrsin⁡90o=1μ, where icricr is the critical angle and μμ is the refractive index of the crystal with respect to air.

⇒μ=1sinicr=1sin45o=2–√.⇒μ=1sin⁡icr=1sin⁡45o=2.

According to Brewster’s law, the tangent of the polarising angle is equal to the refractive index of the refracting medium at which partial reflection takes place.

⇒tanip=μ,⇒tan⁡ip=μ, where ipip is the polarising angle.

⇒ip=arctanμ=arctan2–√=54.74o.⇒ip=arctan⁡μ=arctan⁡2=54.74o.

⇒⇒ The polarising angle is 54.74o.54.74o.