In fig., light of wavelength `lambda = 5000 Å` is incident on the slits (in a horizontally fixed place).
Here, `d = 1 mm` and `D = 1 m`
Take origin at O and XY plane as shown in the figure. The screen is released from rest from the initial position as shown

The velocity of central maxima at `t = 5 `s is

Options

A. `50ms^(-1)` along Y-axis
B. `50ms^(-1)` along negative Y-axis
C. `25ms^(-1)` along Y-axis
D. `3xx10^(8)ms^(-1)` along Y-axis

Answer

A

Explanation

At any instant of time 't', the situtation is shown is figure. The central maxima always lies along Y-axis at `P_(0)`. Its velocity at any time 't' is v = gt along positive Y - axis. `v = gt = 10xx5=50 ms^(-1)`