Which of the following is different from others?

Write the equation of the relation between wave speed $(v)$,angular frequency $(\omega)$,and angular wave number $(k)$.

Define wave speed.

$A$ body sends a wave $150 \text{ mm}$ long through medium $P$ and $0.30 \text{ m}$ long in medium $Q$. If velocity of the wave in medium $P$ is $80 \text{ cm s}^{-1}$, the velocity of wave in medium $Q$ is (in $\text{ m s}^{-1}$)

The transverse displacement $y(x, t)$ of a wave on a string is given by $y(x, t) = e^{-(ax^2 + bt^2 + 2\sqrt{ab}xt)}$. This represents:

The phase difference between two points separated by $0.8 \ m$ in a wave of frequency $120 \ Hz$ is $90^o$. Then the velocity of the wave will be ............ $m/s$.