Questions
Light enters at an angle of incidence in a transparent rod of refractive index n. For what value of the refractive index of the material of the rod the light once entered into it will not leave it through its lateral face what so ever be the value of angle of incidence?
detailed solution
Correct option is A
Let a ray of light enter at A and the refracted beam is AB. This is incident at angle θ . For no refraction at the lateral face, θ>C or, sinθ>sinC But θ+r=900⇒θ=900−r∴sin900−r>sinC Or cosr>sinC..................................iFrom Snell’s law, n=sinisinr⇒sinr=sinin ∴cosr=1−sin2r=1−sin2in2∴ equation (i) we get 1−sin2in2>sinC⇒1−sin2in2>sin2CAlso, sinC=1n∴ 1−sin2in2>1n2 or 1>sin2in2+1n2Or 1n2sin2i+1<1 or n2>sin2i+1Maximum value of sini=1 Hence n2 > 2 ⇒n > 2Talk to our academic expert!
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A light ray from air is incident (as shown in figure) at one end of a glass fiber (refractive index = 1.5) making an incidence angle of 60° on the lateral surface, so that it undergoes a total internal reflection. How much time would it take to traverse the straight fiber of length 1 km
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