I have created this topic to exchange views on the questions from past papers. How they should be attempted and what should be written ? what is out of the blue and what is easy ???

I have one simple confusion. Its stupid though but i really want to make myself clear

There is a question in 2009 Paper I Question no.6 which has its part as Explain ONE INTERFEROMETER . ?

I am confused that are we suppose to explain michelson Interferometer or what ??? Your views required !