Question

Coherent electron beam is being used in YDSE. On increasing accelerating voltage, fringe width will

• A. decrease
• B. remain unchanged
• C. increase
• D. may increase or decrease

Answer 1

The correct option is A decrease

$\lambda =\frac{h}{p}=\frac{h}{\sqrt{2mk}}=\frac{h}{\sqrt{2meV}}$
So when Voltage $\uparrow$, $\lambda$ $\downarrow$.
Since fringe width $B=\frac{D\lambda }{d}$
hence B $\downarrow$.