# Explain why two loudspeakers emitting sound of the same frequency and amplitude, connected to the same signal generator, can produce regions of silence at certain positions in front of them.

> IB DP Physics Standard Level (2023 syllabus) — C.2 Wave model · Explain · 4 marks

> Two loudspeakers are placed side by side, both connected to the same signal generator so that they emit sound waves of identical frequency, amplitude, and phase.

## Mark scheme (4 marks)

1. The two loudspeakers act as two coherent sources, emitting waves with a constant phase relationship.
2. At certain positions the path difference between the two waves is a half-integer number of wavelengths (e.g. λ/2, 3λ/2, …), causing the waves to arrive out of phase.
3. The two waves superpose / interfere destructively at those positions.
4. The crests of one wave coincide with the troughs of the other, so the resultant amplitude is zero and no sound is heard.

## Key terms

- [amplitude](https://www.gradenine.co.uk/glossary/amplitude)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-two-loudspeakers-emitting-sound-2ecda2cb) · Published by Druglandscape Ltd.