Waves, measurement and refraction
| English | 中文 | Pinyin |
|---|---|---|
| frequency/ˈfriːkwənsi/ | 频率 | pín lǜ |
| wavelength/ˈweɪvleŋθ/ | 波长 | bō cháng |
What would explain this observation?
- A wave can carry energy across water while a floating marker mainly oscillates. Energy transfer and bulk transfer of matter are different.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Frequency 频率 is oscillations per time; wavelength 波长 is distance between successive points in phase. Wave speed equals frequency multiplied by wavelength. Transverse oscillations are perpendicular to propagation.
- wavelength: Distance between successive points in phase; frequency: Number of oscillations per unit time.
When a wave enters a slower medium, what stays constant?
At a boundary, frequency stays fixed by the source. A change of speed changes wavelength. Refraction follows from speed differences; angles are measured from the normal.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- At a boundary, frequency stays fixed by the source. A change of speed changes wavelength. Refraction follows from speed differences; angles are measured from the normal.
- Measure several wavelengths and divide to reduce fractional reading uncertainty. Use a ray box with a normal drawn at the boundary. Keep the beam away from eyes and record incident and refracted angles clearly.
Which two habits make the investigation or model in this case more defensible?
Measure several wavelengths and divide to reduce fractional reading uncertainty. Use a ray box with a normal drawn at the boundary. Keep the beam away from eyes and record incident and refracted angles clearly.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: frequency 5 Hz and wavelength 0.40 m. Use v = fλ. v = 5×0.40 = 2.0 metres per second. If speed falls to 1.5 metres per second at the same frequency, wavelength = v/f = 1.5/5 = 0.30 m.
Frequency is 8 Hz and wavelength is 0.25 m. Find wave speed. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Frequency is 8 Hz and wavelength is 0.25 m. Find wave speed.
The result is 2 m/s. Known: frequency 5 Hz and wavelength 0.40 m. Use v = fλ. v = 5×0.40 = 2.0 metres per second. If speed falls to 1.5 metres per second at the same frequency, wavelength = v/f = 1.5/5 = 0.30 m.
Check the conclusion and its limits
- The wave frequency does not change simply because the medium changes. A longitudinal wave has oscillations parallel to propagation.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Wave frequency always changes when a wave enters a new medium. This claim is false: The wave frequency does not change simply because the medium changes. A longitudinal wave has oscillations parallel to propagation.
Waves, measurement and refraction: At a boundary, frequency stays fixed by the source. A change of speed changes wavelength. Refraction follows from speed differences; angles are measured from the normal.
Wave frequency always changes when a wave enters a new medium.
The wave frequency does not change simply because the medium changes. A longitudinal wave has oscillations parallel to propagation.
Distance between successive points in phase: write the technical term.
wavelength means Distance between successive points in phase.