A ray of light incident on the horizontal surface of a glass slab at 70°  just grazes the adjacent vertical surface after refraction,Find critical angle and refractive index of glass
 

Dear Student,

Please find below the solution to the asked query:

sinisinr=nsin70sinr=nsinr=sin70n=0.94nIn the next vertical surface the incident angle will be θi=90-r, and refractive angle is 90 degree. So we havesin(90-r)sin90=1ncosr=1nNow squaring and adding we get1n2+0.942n2=11n21+0.942=1.88n2=1n=1.88=1.37So critical angle is θc=sin-11n=46.88

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