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Coherence - a practical approach

Many first-year degree students ask 'What conditions are necessary for diffraction patterns to be formed?' and, usually after some clues have been given, it is likely that some mention of the necessity for 'the light to be coherent' is elicited. As the topic of coherence is often treated very briefly in textbooks used for sixth-form courses, it is hardly surprising that students seem to be unclear as to what is really meant by coherence. The approach to coherence described has been used with students on degree courses in the Department of Physical Sciences, Wolverhampton Polytechnic, and has been found to be successful in giving students a clearer understanding of the concept as well as preparing them for a more mathematical treatment.