CBSE Class 12 · 2018 · Wave OpticsShort Answer

WhatsApp Email

(a) If one of the two identical slits producing interference in Young's experiment is covered with glass, so that the light intensity passing through it is reduced to

50%

, find the ratio of the maximum and minimum intensity of the fringe in the interference pattern.
(b) What kind of fringes do you expect to observe if white light is used instead of monochromatic light?

Solution

(a) Let the two slits have intensities

I_{1} = I

and

I_{2} = \frac{I}{2}

(one reduced to

50%

). For interference,

\frac{I _{ma x}}{I _{min}} = (\frac{I _{1} + I _{2}}{I _{1} - I _{2}})^{2} = (\frac{I + I /2}{I - I /2})^{2}

Dividing numerator and denominator by

I

\frac{I _{ma x}}{I _{min}} = (\frac{1 + \frac{1}{2}}{1 - \frac{1}{2}})^{2} = (\frac{2 + 1}{2 - 1})^{2}

\frac{I _{ma x}}{I _{min}} = (\frac{2 + 1}{2 - 1})^{2} \approx 33.9

(b) With white light the central fringe is white (zero path difference for all colours); on either side a few coloured fringes appear (violet nearest the centre, red farther out) because the fringe width

β \propto λ

differs for each colour. Beyond a few orders the colours overlap and the pattern becomes uniform white.

CBSE Class 12 Board · 2018 · Subjective

Practise more: all CBSE board PYQs on Wave Optics →

CBSE Class 12 · 2018 · Wave OpticsShort Answer

Solution

More board questions on Wave Optics