Waves, sound, light and magnetic effects
Use wave relationships and distinguish propagation, reflection, refraction and magnetic interactions.
What you will tackle
- Use wavelength, frequency, amplitude and wave speed
- Distinguish sound and electromagnetic waves
- Interpret reflection/refraction and intensity evidence
- Reason about magnets and current-produced fields
Wave quantities
Frequency counts cycles per second; wavelength is distance between matching phases; wave speed v = fλ. Amplitude measures disturbance size rather than wavelength. Sound requires a material medium; electromagnetic waves, including visible light, can travel through a vacuum. A larger amplitude can correspond to greater wave energy without requiring a frequency change.
Interactions and fields
Reflection returns a wave from a boundary; refraction changes its direction when speed changes across a boundary, except at normal incidence where direction can remain unchanged. Frequency stays fixed across a stationary boundary, so wavelength changes with speed. Like magnetic poles repel and unlike poles attract; an electric current produces a magnetic field, whose direction reverses when current reverses. Magnetic-field lines are a representation, not material strings.
Build your notes, then practise
Work on paper before opening an explanation. Guided tasks provide a starting point; independent tasks remove the scaffolding; application tasks ask you to justify a method or interpretation in context.
Guided practice
Guided 1
A wave has frequency 5 Hz and wavelength 2 m. Find its speed and the wavelength if frequency doubles while speed stays fixed. State whether sound or light can cross a vacuum. Predict the interaction of two north poles.
Show a starting hint
State which quantity is held fixed before predicting a change.
Compare with the explained answer
- v = 5·2 = 10 m/s; at 10 Hz the wavelength is 10/10 = 1 m.
- Light can propagate through vacuum; sound cannot in this introductory model.
- Two north poles repel; a north and south pole attract.
Answer / response criteria: 10 m/s; 1 m; light; repulsion.
Independent practice
Independent 1
Light crosses a stationary boundary and slows from 3 to 2 speed units while frequency stays 6 frequency units. Compare wavelengths. A sound wave's amplitude increases with unchanged frequency: must its pitch rise? A current reverses in a wire: what magnetic property changes direction?
Compare with the explained answer
- The wavelength changes from 3/6 to 2/6 units, a factor of 2/3.
- An amplitude increase alone does not require higher frequency or pitch; the frequency is specified unchanged.
- The current-produced magnetic-field direction reverses.
Answer / response criteria: Wavelength becomes two-thirds; no required pitch rise; magnetic-field direction reverses.
Application practice
Application 1
An ideal-light dataset gives intensity 36,9,4 at distances 1,2,3. Test an inverse-square model and predict at 4. Explain why a reflected wave and a refracted wave are different outcomes, and why a straight path at normal incidence does not prove unchanged speed.
Compare with the explained answer
- Id² is 36 at all three distances, fitting I = 36/d² and predicting 2.25 at 4, beyond the measured range.
- Reflection returns a wave at the boundary; refraction concerns transmission with changed speed and potentially changed direction.
- At normal incidence speed and wavelength can change without the transmitted direction turning; direction alone is insufficient.
Answer / response criteria: Inverse-square fit and qualified prediction 2.25; boundary outcomes and the normal-incidence limit as stated.
What can you explain now?
An ideal-light dataset gives intensity 36,9,4 at distances 1,2,3. Test an inverse-square model and predict at 4. Explain why a reflected wave and a refracted wave are different outcomes, and why a straight path at normal incidence does not prove unchanged speed.
Compare with the explanation
Inverse-square fit and qualified prediction 2.25; boundary outcomes and the normal-incidence limit as stated.
Explain the reasoning before comparing. This review records your self-assessment rather than an official score or mastery decision.
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Source and review status
Coverage follows the named requirements and examples in the 2026–2027 ACT test guide and subject descriptions. That guide explicitly does not list every possible topic. The broader coded College and Career Readiness Standards are also mapped to conceptual teaching and practice; this does not calibrate a learner to a score band. The separate scientific-background context list and reading-complexity rubric have their own stated limits.
Original teaching and explained self-check practice are available. Specialist review and difficulty calibration remain pending. Essays require self-check or teacher review and are not automatically marked or awarded official scores.
Official source specification / guide