Waves 20.1 READ A wave is a traveling oscillator that carries energy from one place to another. A high point of a wave is called a crest. A low point is called a trough. The amplitude of a wave is half the distance from a crest to a trough. The distance from one crest to the next is called the wavelength. Wavelength can also be measured from trough to trough or from any point on the wave to the next place where that point occurs. Amplitude One wavelength is crest to crest Crest Trough The speed of a wave Frequency (hertz) Speed (m/sec)-. v = f 2- Wavelength (meters) EXAMPLE The frequency of a wave is 40 Hz and its speed is 100 meters per second. What is the wavelength of this wave? Given Solution Frequency = 40 Hz; Speed = 100 m/sec 100 m/sec 100 m/sec = Wavelength Looking for 40 Hz 40 cycles/sec The wavelength 2.5 meters = Wavelength Relationships Speed = Frequency x Wavelength, therefore The wavelength of this wave is 2.5 meters. Speed + Frequency = Wavelength PRACTICE 1. On the graphic at right label the following parts of a wave: one wavelength, half of a wavelength, the amplitude, a crest, and a trough. centimeters a. How many wavelengths are represented in the wave above? b. What is the amplitude of the wave shown above?Page 2 of 2 PRACTICE 112m 2. Use the grids below to draw the following waves. Be sure to label the y-axis to indicate the 20.1 measurement scale. a. A wave with an amplitude of I cm and a wavelength of 2 cm b. A wave with an amplitude of 1.5 cm and a wavelength of 3 cm 3. A water wave has a frequency of 2 hertz and a wavelength of 5 meters. Calculate its speed. 4. A wave has a speed of 50 m/sec and a frequency of 10 Hz. Calculate its wavelength. 5. A wave has a speed of 30 m/sec and a wavelength of 3 meters. Calculate its frequency. 6. A wave has a period of 2 seconds and a wavelength of 4 meters. Calculate its frequency and speed. Note: Recall that the frequency of a wave equals 1/period and the period of a wave equals 1/frequency. 7. A sound wave travels at 330 m/sec and has a wavelength of 2 meters. Calculate its frequency and period. 8. The frequency of wave A is 250 hertz and the wavelength is 30 centimeters. The frequency of wave B is 260 hertz and the wavelength is 25 centimeters. Which is the faster wave? 9. The period of a wave is equal to the time it takes for one wavelength to pass by a fixed point. You stand on a pier watching water waves and see 10 wavelengths pass by in a time of 40 seconds. a. What is the period of the water waves? b. What is the frequency of the water waves? c. If the wavelength is 3 meters, what is the wave speed