Distinguish interference patterns

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: At one point two modeled displacements are +3 and -2 mm. Predict the combined displacement.
• Assessment case 1: At one point two simultaneous displacements are+2 and+5 mm. What is predicted? Which inference or prediction is best supported?
• Assessment case 2: Which interference phenomenon describes the local reinforcement or cancellation? Supplied case: Equal upward and downward displacements cancel locally.
• Assessment case 3: Which cycle property or general combination rule is specifically described? Supplied case: Two crests occur at matching cycle positions.
• Assessment case 4: Which cycle property or general combination rule is specifically described? Supplied case: Result found by adding signed displacements.
• Assessment case 5: Which interference phenomenon describes the local reinforcement or cancellation? Supplied case: Equal downward displacements reinforce.
• Assessment case 6: At one point displacements are+4 and−1 mm. What follows? Which inference or prediction is best supported?

Learn the idea

Overlapping waves combine by superposition in the model. In-phase displacements can reinforce; opposite displacements can partly or fully cancel at a point. Energy is redistributed, not simply destroyed.

Constructive means displacements reinforce at this point. Destructive means opposing displacements reduce result. Phase means position within the wave cycle. Superposition means combined displacement is sum of contributions.

For the supplied mechanism problem, At one point two modeled displacements are +3 and -2 mm. Predict the combined displacement. Superposition gives +3+(-2)=+1 mm. Opposing displacements partially cancel at that point; the result is not zero unless magnitudes match. Local cancellation does not mean all wave energy is destroyed.

1. Read the supplied problem and mark the structures, processes or quantities named: At one point two modeled displacements are +3 and -2 mm. Predict the combined displacement.
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New superposition case: displacements are -4 mm and +1 mm at one point. Expected: combined displacement -3 mm; opposing signs partially cancel without proving all wave energy disappeared.

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