When two coherent sources interact with each other, there will be production of alternate bright and dark fringes on the screen . Young's double-slit experiment domonstrates the idea of making two coherent sources. For better visibility, one has to choose proper amplitude for the sources. The phenomena is good enough to satisfy the conservation of energy principle. The pattern formed in YDSE is of uniform thickness and is nicely placed on a long distance screen.
For better visibility of fringe pattern

Options

A. amplitude of the sources are equal
B. the width of the slits should not be equal
C. dark should be the darkest and bright should be the brightest
D. the widths should be same

Answer

a.,c.,d

Explanation

If `A_(1) = A = a, I_(max) = 4a^(2), I_(min) = 0`. So, visibility is the best.
Choice (a) is correct.
Since `I_(min) = 0`, (c ) is aslo correct.
width decides intensity and thereby the amplitude. So, choice (d) is correct making (b) wrong.