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💡 Drawing sound
Plot the air’s density against distance and the invisible sound wave turns into a familiar wavy line with peaks and valleys.
What are crest and trough on a density graph?
- Plot density (y-axis) against distance (x-axis) at one instant; the average density is a dashed line.
- The highest point (maximum density, a compression) is a crest .
- The lowest point (minimum density, a rarefaction) is a trough .
📚 Ready to Go Beyond
Another way to represent a sound wave graphically is to plot the variation of density of the medium with time , at one fixed location in the medium.
NCERT Question 7 — Draw a graph to represent
Draw a graph to represent a sound wave for which the density amplitude is 3 units and wavelength is 4 cm.
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Important Definitions
- Crest — the point of maximum density on a density-distance graph, i.e. a compression.
- Trough — the point of minimum density on a density-distance graph, i.e. a rarefaction.
