Wave Practice Homework Solutions

Key One full wave (cycle) Wave train: two or more waves Amplitude: measures the energy of a transverse wave Measured from the equilibrium position to the top of a crest or the bottom of a trough   Wavelength: length of a single wave cycle Frequency: number of waves that pass a point in a given amount of time Speed = wavelength x frequency Period = 1/frequency Wave 1 (Time elapsed below is 1 second) Diagram: A wave train with 5 waves. Problems: a) How many waves are there in this wave train? 5 b) Frequency = 5 Hz c) Velocity of wave = 50 m/s d) Period = 1/5 = 0.2 s Wave 4 (Time elapsed below is 0.5 seconds) Diagram: A wave train with 8 waves. Problems: a) How many waves are there in this wave train? 8 b) Frequency = 16 Hz c) Velocity of wave = 80 m/s d) Period = 1/16 = 0.0625 s Problems What is the wavelength of a sound wave with a frequency of 50 Hz? (Speed of sound is 342 m/s) Solution: V = f * λ 342 = 50 * λ λ = 6.84 m Problem 2: Given: Frequency of a sound wave in a steel rail is 620 Hz, wavelength is 10.5 m. Find: Speed of sound in steel. Solution: V = f * λ V = 620 * 10.5 V = 6510 m/s Problem 3: Given: Wavelength of a radio wave is 2500 meters, speed of light is 300,000,000 m/s. Find: Frequency of the radio wave. Solution: 300,000,000 = f * 2500 f = 120,000 Hz Problem 4: Given: Frequency of a radio wave is 120,000 Hz. Find: Period of the radio wave. Solution: Period = 1/f Period = 1/120,000 Period = 8.3 * 10^-6 Problem 5: Explain the Doppler Effect and why a star moving away appears red. Solution: As a star moves away, the light waves it emits are stretched, resulting in a lower frequency. Lower frequency corresponds to red light. Problem 6: Identify the tuning fork with the longest wavelength and the lowest pitch sound. Solution: Longest wavelength: 242 Hz Lowest pitch sound: 242 Hz Problem 7: Match the colors of visible light to their probable frequencies based on the electromagnetic spectrum. Solution: 400: Red 526: Green 668: Violet