Students will be working in pairs. Each pair needs:
- 1 index card with 2 slits cut in it (see image below)
- 4 strips of paper – take 1 sheet of paper oriented in landscape (horizontal) then cut it horizontally into 4 strips
In your pairs, set up your index card with one strip of paper like so:
Click here for the directions on PowerPoint PPT
(This is also a good time to check for understanding whether your students can distinguish between wave frequency and wave speed (velocity). Often, students lump the two together in the description, “it’s fast”.)
To check for understanding of the directions and to strengthen connection between vocabulary (wave speed and frequency) and concept, ask clarifying statements such as:
- “Who controls the wave speed? The person moving the pen, or the person pulling the paper?” “Who controls the wave frequency? The person moving the pen, or the person pulling the paper?”
- How might you increase the wave frequency?
- If the person pulls the paper faster, are they increasing wave speed or wave frequency?
Avoid and discourage using terms like “fast” and “slow” without relating it to speed or frequency. A potential difficulty and point of confusion for students is distinguishing between speed and frequency (because both can be described as “fast” or “slow”), so help students distinguish the two by using them in context yourself and asking them to clarify if they describe something as “fast” or “slow” in isolation.
Example:
S: For this one, it was fast.
T: What was fast? There was a high speed, or high frequency?
S: ……………… um…………………………………………………………………. ………………………………………………………………………………. [proper wait time]
T: You moved your hand fast, or you moved the paper fast?
S: …………we moved our hand fast.
T: So that means high wave speed or high frequency?
S: …………………… high………….. frequency.
Students should end up with a total of 4 sets of waves on their 4 strips of paper.
Look at the two strips you labeled “Low frequency” and “High frequency”. Do they have the same wavelengths or different wavelengths? Which one has shorter wavelengths? Why? Would we say that the frequency of a wave and wavelength of a wave are directly proportional or inversely proportional?
Now, look at the two strips you labeled “Low speed” and “High speed”. Do they have the same wavelengths or different wavelengths? Which one has longer wavelengths? Why? Would we say that the speed of a wave and wavelength of a wave are directly proportional or inversely proportional?
How does this experiment relate to our wave equation, wavelength = velocity/frequency?
Objectives:
- Build fluency with wave terms: speed (velocity) vs frequency
- Understand the relationship represented by the wave equation λ=v/f