In an optical fibre, if the total internal reflection takes place, which of the following conditions have to be satisfied?

A. $${n_2} > {n_1}{\text{ and }}{\phi _1} > {\cos ^{ - 1}}\left( {\frac{{{n_2}}}{{{n_1}}}} \right)$$

B. $${n_2} < {n_1}{\text{ and }}{\phi _1} > {\cos ^{ - 1}}\left( {\frac{{{n_2}}}{{{n_1}}}} \right)$$

C. $${n_1} < {n_2}{\text{ and }}{\phi _1} < {\cos ^{ - 1}}\left( {\frac{{{n_2}}}{{{n_1}}}} \right)$$

D. $${n_1} > {n_2}{\text{ and }}{\phi _1} > {\cos ^{ - 1}}\left( {\frac{{{n_2}}}{{{n_1}}}} \right)$$

Answer: Option B