Answer the following questions with reference to step-index optical fibres.
a. (i) Distinguish between single-mode and multimode fibres on the basis of core diameter and nature of light propagation.
b. (ii) Explain why single-mode fibres provide larger bandwidth and lower pulse dispersion than multimode fibres.
c. (iii) Give one practical application where a multimode fibre is preferred and one where a single-mode fibre is preferred, stating the reason for each choice.