Question

At $t=2s$, the position of central maxima is

• A. $2mm$ above $C$
• B. $2mm$ below $C$
• C. $4mm$ above $C$
• D. $4mm$ below $C$

Answer 1

The correct option is B $2mm$ below $C$

Path Difference from Source:

${\delta }_{Source}=\frac{1\times {10}^{-3}\times 2\times {10}^{-3}}{1}$

Path Difference on the screen:

$\delta =\frac{x\times 2\times {10}^{-3}}{2}$

For Central Maxima:

${\delta }_{Source}=\delta$

Which gives $x=2mm$

And as the source is above, the central fringe will be below the central horizontal axis.

Answer is B: 2mm below C