Science lesson plan · 9th grade (Year 10 in England) · 45 minutes
Wave speed = frequency × wavelength
Light, sound and waves
CCSS NGSS.HS-PS4-1England: KS4 Combined Science: Waves in matter
Objective and success criteria
Students will: Wave speed = frequency × wavelength.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Parts of a wave
Leads to: The electromagnetic spectrum; Period and frequency (T = 1 / f)
Materials: Slinky or rope, Mirrors and torches, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Parts of a wave). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- 20 waves pass a point in 5 seconds. What is the frequency, in hertz (Hz)? → 4 HzPrompt: Frequency is the number of waves per second.
- Is this a transverse or a longitudinal wave: sound in air? (transverse / longitudinal) → longitudinalPrompt: Do the particles move up and down, or back and forth along the wave?
- 6 waves pass a point in 2 seconds. What is the frequency, in hertz (Hz)? → 3 HzPrompt: Frequency is the number of waves per second.
Hook · 5 min
- Ask the class to make a wave with a rope or slinky and describe what moves and what doesn't.
- Share the objective: Wave speed = frequency × wavelength. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A wave has a frequency of 10 Hz and a wavelength of 4 m. What is its speed, in m/s?
- Step 1: v = 10 × 4 = 40
- Step 2: So the answer is: 40 m/s
- Answer: 40 m/s
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A wave has a frequency of 200 Hz and a wavelength of 3 m. What is its speed, in m/s? → 600 m/sPrompt: v = f × λ
- Sound travels at 340 m/s in air. What is the wavelength of a 85 Hz sound, in metres? → 4 mPrompt: Rearrange v = f λ to find λ.
You do: independent practice · 10 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Sound travels at 340 m/s in air. What is the wavelength of a 85 Hz sound, in metres? → 4 mPrompt: Rearrange v = f λ to find λ.
- A wave has a frequency of 50 Hz. What is its period (the time for one wave), in seconds? → 0.02 sPrompt: Period T = 1 ÷ frequency.
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: Parts of a wave.
- Use concrete materials: slinky or rope.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: The electromagnetic spectrum; Period and frequency (T = 1 / f).
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.
Free lesson plan from eurekami.com/lesson-plan-builder