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When the surface of a lake is calm , a f...

When the surface of a lake is calm , a fish submerged in water will see the entire outside world within an inverted cone whose vertex is situated at the eye of the fish . What is the vertex angle of the cone ?
`(""_(a) n_(w) = (4)/(3))` and `sin 49^(@) = 0.75`

A

`110^(@)`

B

`98^(@)`

C

`48^(@)`

D

`68^(@)`

Text Solution

Verified by Experts

The correct Answer is:
B

`""_(a) n_(w) = (4)/(3)`
If C is the critical angle , then
`sin C = (1)/(""_(a) n_(w)) = (1)/(4//3) = (3)/(4) = 0.75`
`therefore C = sin^(-1) (0.75^(@)) = 90^(@)`
`therefore` Vertex angle of the cone = `2 xx 49^(@) = 98^(@)`
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