Study guide: Waves, Sound and Light

A worked review example

Worked supplied problem: An ideal vacuum chamber contains a radio transmitter and a vibrating speaker. Which signal can cross the vacuum? Solution: Electromagnetic radio waves can propagate across the vacuum. Ordinary sound requires a material medium, so the speaker’s mechanical disturbance cannot propagate across the ideal empty gap. This conclusion uses the stated observations and the mechanism explained above; it does not establish every unmeasured feature of a real organism, device or place. Worked distinct example: A distinct record has 24 cycles in 4 seconds: 24/4=6 Hz. Method: identify the quantities in the stated rule, substitute using compatible units, and perform the operations in the correct order. Count cycles, not half-cycle peaks separately. Use seconds for hertz. Interpret the final unit and keep the model assumption visible; this calculation is not a measurement of a real learner or site. Worked supplied problem: A ray enters water obliquely and bends; some energy also enters the water. Explain why one label need not describe everything. Solution: The directional change can be refraction while transmission also occurs. Reflection and absorption may also occur at a real boundary. The supplied diagram establishes only the paths and transfers shown. This conclusion uses the stated observations and the mechanism explained above; it does not establish every unmeasured feature of a real organism, device or place. Worked supplied problem: Two rope patterns have equal amplitude but frequencies 2 Hz and 4 Hz. Explain what changed and what was not established. Solution: The second completes twice as many cycles per second. Equal amplitude means equal maximum displacement in the model. It does not make the wave speeds equal unless the medium and model conditions establish that. This conclusion uses the stated observations and the mechanism explained above; it does not establish every unmeasured feature of a real organism, device or place.