A Level Physics Practice Exam

What describes the effect of continuous ultrasound waves on particles in a medium?

1. Particles move uniformly at all points

2. Particles at nodes experience maximum movement

3. Particles move in phase between two nodes

4. Particles at antinodes do not move at all

The correct answer is: Particles move in phase between two nodes

The effect of continuous ultrasound waves on particles in a medium can be understood through the concept of wave motion. In a medium where ultrasound waves propagate, particles oscillate back and forth around their equilibrium positions as the wave travels through. The correct description states that particles move in phase between two nodes. This means that the particles at various positions in the medium synchronize their oscillatory motions – they reach maximum displacement (either compression or rarefaction) at the same times. This synchronized movement occurs in segments of the wave between points known as nodes. Nodes are positions where the displacement of the medium is always zero due to destructive interference, while the areas between nodes, known as antinodes, experience maximal displacement. In contrast, particles at the nodes do not exhibit any movement since they are defined as points of zero amplitude in the wave. Furthermore, particles at the antinodes experience the greatest movement; it's inaccurate to say they do not move at all. On a broader scale, uniform movement by particles across the medium does not accurately describe wave motion, as particles only oscillate, leading to varying degrees of motion depending on the position relative to nodes and antinodes.