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# In an optical fibre, core and cladding were made with materials of refractive indices 1.5 and 1.414 respectively . To observe total internal reflection , what will be the range of incident angle with the axis of optical fibre?

$\begin {array} {1 1} (1)\;0^{\circ}-60^{\circ} & \quad (2)\;0^{\circ}-48^{\circ} \\ (3)\;0^{\circ}-30^{\circ} & \quad (4)\;0^{\circ}-82^{\circ} \end {array}$

$(3)\;0^{\circ}-30^{\circ}$