7) A

The amplitude is the maximum displacement of a wave from its CENTRE.

The amplitude of this wave is (16 – 10)/2 = 3m

We know that ƒ=1/T

Time period (T) is the total time taken for one oscillation, i.e. time between 2 consecutive troughs or peaks. On the x axis, the time is given. Let us take the peaks at 6 hours and 18 hours. This gives us a

value for T = 12 hours = 12 x 3600s

Hence, ƒ = 1/(12×3600)

A = 3m, ƒ = [1 / (12×3600)]. This corresponds to option A.