Question

In a YDSE, the central bright fringe can be identified by which of the following?
A. As it has a greater intensity than the other bright fringes.
B. As it is wider than the other bright fringes
C. As it is narrower than the other bright fringes
D. By using white light instead of single wavelength light

Answer 1

Hint- YDSE stands for young's double slit experiment. In this experiment light is passed through two narrow slits and these lights will form an interference pattern on a screen placed at a distance d.
Bright fringes are formed when path difference between two slits to the fringe is an integral multiple of wavelength
Dark fringes are formed when the path difference is half integral multiple of wavelength
At the centre path difference is 0.
If you use white light since white light consists of the seven colours, the central bright fringe will be a combination of the central maxima of all seven colours. We can see different coloured fringes except at the central bright fringe which is white

Step by step solution:
YDSE stands for young's double slit experiment. In this experiment light is passed through two narrow slits and these lights will form an interference pattern on a screen placed at a distance d.
When monochromatic light is passed through two narrow slits and falls on a distance screen. A pattern of dark and bright fringes is observed. This happens due to interference caused due to superposition of waves coming from the two slits. Regions with high intensity e and low intensity are formed. At the places where constructive interference takes place, we get bright fringes and at places where destructive interference takes place, we get dark fringes.
At the centre the fringe will have maximum intensity which is known as a central maximum. if we use monochromatic light then these fringes can be distinguished using the fact that it will be the brightest among the bright fringes.
Bright fringes are formed when path difference between two slits to the fringe is an integral multiple of wavelength
Dark fringes are formed when the path difference is half integral multiple of wavelength
At the centre path difference is 0.
If you use white light since white light consists of the seven colours, the central bright fringe will be a combination of the Central Maxima of all seven colours. Hence this region will be white but the other bright fringes will be formed at different places depending upon the frequency of each colour. So, we can see different coloured fringes except at the central bright fringe which is white. Hence it is very easy to distinguish it with the other coloured fringes.

So, option D is correct.

Note: The identification of the Central bright fringe is easier using white light. In order to study the interference pattern clearly white light cannot be used. Because of the difference in width and intensity and overlapping of the maxima of different colours at places other than the central Maxima it is difficult to study the characteristics. Hence young's double slit experiment is conducted using a monochromatic source of light to get a clear interference pattern. In that case the central bright fringe can be identified depending upon the intensity. Intensity will be maximum at the centre.