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Wave Properties
Frequency, Wavelength, Speed, Amplitude, and Period
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Waves transfer energy from one place to another without requiring matter to move along with the wave over large distances. Three of the most important wave properties are frequency, wavelength, and speed. These quantities help describe everything from sound and light to vibrations on strings and water waves. Understanding how they are related lets students predict how waves behave in different situations.
Frequency tells how many cycles pass a point each second, wavelength measures the distance between matching points on consecutive cycles, and wave speed tells how fast the disturbance travels. These quantities are linked by the equation v = fλ. If the wave speed stays constant, increasing frequency causes wavelength to decrease. This relationship is used in optics, acoustics, telecommunications, and many other areas of physics.
Key Facts
- Wave speed is given by v = fλ
- Frequency f is measured in hertz, where 1 Hz = 1 cycle/s
- Wavelength λ is the distance between two consecutive crests or two consecutive troughs
- Amplitude is the maximum displacement from the equilibrium line
- Period and frequency are related by T = 1/f
- For a wave traveling in the same medium, higher f means smaller λ if v stays constant
Vocabulary
- Frequency
- Frequency is the number of complete wave cycles that pass a point each second.
- Wavelength
- Wavelength is the distance between identical points on neighboring cycles of a wave.
- Amplitude
- Amplitude is the maximum distance from the equilibrium position to a crest or trough.
- Period
- Period is the time required for one complete wave cycle.
- Wave speed
- Wave speed is the rate at which the wave disturbance moves through a medium or space.
Common Mistakes to Avoid
- Using amplitude in the speed equation, which is wrong because wave speed depends on frequency and wavelength through v = fλ, not on amplitude in this basic relation.
- Confusing frequency and period, which is wrong because they are reciprocals, so a larger frequency means a smaller period.
- Measuring wavelength from a crest to the nearest trough, which is wrong because that distance is only half a wavelength.
- Changing frequency without adjusting wavelength in the same medium, which is wrong because if speed stays constant then λ must decrease when f increases.
Practice Questions
- 1 A wave has frequency 5 Hz and wavelength 2 m. What is its speed?
- 2 A sound wave travels at 340 m/s and has frequency 170 Hz. What is its wavelength?
- 3 Two waves travel in the same medium. One has a higher frequency than the other. Explain how their wavelengths compare and why.