[填空题]
A longitudinal wave travels through a medium from left to right. Graph 1 below shows how the displacement $x$ of a particle $P$ in the medium varies with time. Positive displacement is to the right.
1.Describe what is meant by a longitudinal wave.
2.Use the graph to determine:
(1)the amplitude of the wave mm
(2)the frequency of the wave f = Hz
(3)the direction of motion of the particle at $t=10ms$.
3.Graph 2 below shows variations of displacement of particles in the medium with distance from the source of wave at an instant in time.
(1)Use the graph to calculate the speed of the wave. State an appropriate unit for your answer. v = $ms^{-1}$
(2)Label with the letter C a position on the graph at the center of a compression, and a letter R at the center of a rarefaction.
Graph 1 showing the displacement of particle P with time is reproduced below.
A second source is added to the medium that generates identical waves $14\,cm$ closer to $P$ than the original source.
4.Draw a second dotted line to show how the displacement, $x$ of a particle in the medium would vary with time due solely to the second source.
