IIT-JEE 2010 · Paper 2 · Physics Q48

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PhysicsInteger+3Question 48 of 57

A large glass slab ( $\mu=5/3$ ) of thickness 8 cm is placed over a point source of light on a plane surface. It is seen that light emerges out of the top surface of the slab from a circular area of radius $R$ cm. What is the value of $R$ ?

Your answer

Answer and worked solution

Official answer: 6

Critical angle. $\sin C=\frac35$ , so $\tan C=\frac34$ .

Radius of the bright circle. Light escapes only within the cone of half-angle C: $R=8\tan C=6$ cm.

Answer: 6

Topics:Total internal reflection

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IIT-JEE 2010 · Paper 2, Physics question 48