Year 9 Science · Unit 4 · Lesson 3
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Learning Goals
Read the graph
Approximate frequencies of four common wave types
Note: bar heights are schematic (logarithmic scale) — visible light is approximately 500 000 000 000 000 times higher frequency than seismic P-waves. Data: Physics Reference Tables, NESA NSW.
(a) Which wave type shown has the highest frequency, and which has the lowest? What does this suggest about which carries the most energy per photon?
(b) A sound wave in air has a frequency of 500 Hz. The speed of sound is 340 m/s. Calculate the wavelength of this sound wave (λ = v ÷ f). Show your working.
(c) If all four wave types travelled at the same speed, which would have the longest wavelength? Explain your reasoning using the relationship between frequency and wavelength.
Real-world context
An audiologist at a Sydney hearing clinic uses an oscilloscope to display two sound waves produced by different audio sources. Wave A has an amplitude of 3 cm on the display and a frequency of 200 Hz. Wave B has an amplitude of 6 cm and a frequency of 400 Hz. The audiologist needs to compare the loudness, pitch, and energy of the two waves for a patient with partial hearing loss.
(a) Which wave would the patient hear as louder, and why? Use the relationship between amplitude and energy in your answer.
(b) Which wave would the patient hear as higher-pitched, and why? Explain what determines the pitch of a sound.
(c) Calculate how many times more energy Wave B carries compared to Wave A. Use the relationship energy ∝ amplitude², and show your working clearly.
Wrap Up
In one sentence, what was the main idea of this lesson?