Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What happens to the reflected pulse when a wave crosses from a less dense to a more dense medium?

1. It remains unchanged

2. It becomes inverted

3. It travels faster

4. It increases in amplitude

The correct answer is: It becomes inverted

When a wave crosses from a less dense medium to a more dense medium, the reflected pulse becomes inverted. This behavior can be attributed to the boundary conditions at the interface between the two media. When a wave encounters a denser medium, part of the wave continues to propagate into the new medium, while another part is reflected back. In the case of a wave reflecting at this boundary, the change in density affects how the wave interacts with the medium. Specifically, the denser medium exerts a greater force on the wave, which leads to the flip in the direction of the displacement of the reflected wave. This inversion reflects the change in the speed and impedance of the wave as it transitions from a less dense medium, where waves can travel more freely, to a more dense medium, where they are more tightly bound. The other options do not accurately depict the behavior of the wave in this scenario. The reflected wave does not remain unchanged, as it undergoes an inversion; it does not travel faster, since waves generally slow down when moving into a denser medium; and it does not increase in amplitude as it reflects. In fact, the amplitude may be diminished depending on the amount of energy that is transmitted versus reflected. Thus, the correct understanding of