Year 9 Science · Unit 4 · Lesson 4
Apply Worksheet
Learning Goals
Order the steps
Number the steps from 1 to 6 to show the correct method for solving a wave speed calculation. Step 1 = what you do first.
| Order | Step |
|---|---|
| Calculate the answer (multiply or divide the numbers). | |
| Check that your answer has the correct units (m/s for speed, Hz for frequency, m for wavelength). | |
| Write down what you are given: identify f and λ (or whichever two values you know). | |
| Write the wave equation: v = f × λ. | |
| Substitute the known values with their units into the equation. | |
| Check whether your answer seems reasonable (e.g. sound in air should be close to 343 m/s). |
Real-world context
During a thunderstorm over Sydney, lightning and thunder are produced at the same instant. You see the lightning flash almost immediately, but the sound of thunder travels at approximately 343 m/s in air. You count the seconds between the flash and the thunder to estimate how far away the storm is.
(a) You see a lightning flash and hear the thunder 6 seconds later. Calculate the distance to the lightning bolt. Use: distance = speed × time. Show your working.
(b) A second lightning strike produces thunder that you hear 12 seconds after the flash. How far away is this strike? Is it closer or further than the first strike? Show your working.
(c) Explain why you see the lightning almost instantly but hear the thunder seconds later. Use the wave equation v = fλ and the known speeds of light (3 × 10⁸ m/s) and sound (343 m/s) to justify your answer.
1. A radio station in Melbourne broadcasts at a frequency of 774,000 Hz (774 kHz). All radio waves travel at 3 × 10⁸ m/s. Calculate the wavelength of this radio wave. Show your working.
2. A student says: "If I move from air into water, the frequency of a sound wave I'm hearing will change." Is the student correct? Explain using your knowledge of how the wave equation applies when a wave moves between media.
Wrap Up
In one sentence, what was the main idea of this lesson?