The equation of a plane wave is `y = 3 xx 10^(-0.01 x) cos (600 t - 0.78 x + pi//2)` where units of y, t and x are `10^(-5)` cm, s and m respectively. Write its general expression of phase and also determine
(i) its phase at x = 0, t = 0
(ii) phase difference between the points separated by 25 cm along X-axis.
(iii) amplitude at x = 200 m

Explanation

To solve the given problem step by step, we will follow the instructions provided in the question.

### Step 1: Write the General Expression of Phase
The phase of the wave can be expressed from the wave equation. The wave equation given is:
\[ y = 3 \times 10^{-0.01 x} \cos(600 t - 0.78 x + \frac{\pi}{2}) \]

The general expression of the phase \( \phi \) is:
\[ \phi = 600t - 0.78x + \frac{\pi}{2} \]
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