1.

A parallel beam of white light is reflected from a thin wedge shaped film. The colour of the fringe at the edge of the wedge will be

Answer»

white
red
black
violet

Solution :For a wedge of height h and width l having the index of refraction n, the conditions of maxima and minima are given as follows.
For maxima,
`X=(lamdal(m+1/2))/(2hn),m=0,1,2,...`
For minima, `x=(lamdalm)/(2hn),m=0,1,2,....`
At the edge of the wedge, x = 0
This CORRESPONDS to a MINIMUM at m = 0.
Hence, at edge, black fringe will form.


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