Question

If the source of light used in Young’s double-slit experiment is changed from red to violet:

• A. the fringes will become brighter.
• B. consecutive fringe lines will come closer.
• C. the central bright fringe will become a dark fringe.
• D. the intensity of minima will increase.

Answer 1

The correct option is B

consecutive fringe lines will come closer.

Explantion for the correct option:

Option (C):

Young's double-slit experiment:

1. When single light passes through two narrow slits illuminates a distant screen.
2. A characteristic pattern of bright and dark fringes is observed.
3. This interference pattern is caused by the superposition of overlapping light waves originating from the two slits.
4. It exhibits the wave nature.
5. Fringe width in Young's double-slit experiment is given by:$\beta =\frac{\lambda D}{d}$
6. Red light's wavelength is greater than violet light's wavelength, so fringe width will reduce.
7. Also, the consecutive fringes will come closer.

Explantion for the incorrect options:

Option (A):

1. We generally see the characteristic patterns of bright and dark fringes in Young's double-slit experiment.
2. Hence, the condition of the fringes will become brighter does not occur in this case.

Option (B):

1. In the case of Young's double-slit experiment, the central bright fringe never becomes a dark fringe.
2. Rather, characteristic alternate patterns of bright and dark fringes tend to occur in the given case.

Option (C):

1. In case of Young's double-slit experiment, generally, a characteristic pattern of bright and dark fringes is observed.
2. Here the central bright fringe becoming dark fringe does not occur as a condition.
3. Hence the given option is incorrect.

Hence, option (B) is correct.