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A right angled prism is to be made by selecting a proper material and the angles A and B `(B |
Answer» (`a`) As already discussed `Agetheta_(c )`, `Bgetheta_(c )` Also `BleA` Case : `1 : B=A=pi//4rArrtheta_(c )lepi//4`…..(`1`) Case `2 : B lt A`. Hence, for reflection at both faces `B gt theta_(c )` But, `B lt pi//4rArrtheta_(c ) lt pi//4` (as `2B lt pi//2`).......(`2`) Combining Eqs. (`1`) and (`2`), we get `theta_(c ) le pi//4` `(1)/(n) le(1)/(sqrt(2))rArrn ge sqrt(2)` `n_(min)=sqrt(2)` (`b`) This pertains to case (`2`) Hence, `theta_(c ) lt 30^(@)` But `theta_(c )=sin^(-1)(3//5)` which is more than `30^(@)` and hence, it is not possible. |
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