Question

In Young's double slit experiment, if the separation between slit plane and screen is doubled and the wavelength of coherent light used in two slits is halved, then fringe width -

• A. Becomes half
• B. Remains unchanged
• C. Becomes four times
• D. Becomes one-fourth

Answer 1

The correct option is B Remains unchanged

Fringe width in YDSE is given by,

$\beta =\frac{\lambda D}{d}$

Now,

$D^{{}^{\prime }}=2D$

${\lambda }^{{}^{\prime }}=\frac{\lambda }{2}$

$\Rightarrow {\beta }^{{}^{\prime }}=\frac{\frac{\lambda }{2}\times 2D}{d}=\frac{\lambda D}{d}=\beta$

$\therefore$ Fringe width remains unchanged.