Figure 8 represents a longitudinal wave. Which point is at the centre of a rarefaction?
Answer options:
A.
E
B.
F
C.
G
How to approach this question
A longitudinal wave is made of compressions and rarefactions. A compression is where the particles are close together. A rarefaction is where the particles are spread apart. Identify the letter in the middle of a region where the dots are most spread out.
Full Answer
B.F✓ Correct
F
In a longitudinal wave, like a sound wave, the vibrations are parallel to the direction of energy transfer. This creates areas where the particles of the medium are bunched together, called compressions, and areas where they are spread apart, called rarefactions.
- Point E is in a region where the dots are dense, which is a compression.
- Point F is in a region where the dots are spread out, which is a rarefaction.
- Point G is also in a region where the dots are spread out, a rarefaction. The question asks for one point, and F is a valid choice.
Common mistakes
✗ Confusing compressions (particles close together) with rarefactions (particles spread apart).
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