AS 91523 · 2023 paper · violin tuning

Question 2(d)(i) Merit to Excellence

On a hot day the violin goes out of tune easily, and Sam has to adjust the tension in the "G" string to keep it vibrating at 196 Hz.

When Sam plays a frequency of 564 Hz near a wine glass, the glass rattles on the shelf.

Describe this phenomenon, as part of an in-depth explanation of it.

The 2023 paper, page 5 ↗ Marking schedule, page 3 ↗

Work it out

Try it on paper first. Stuck? Take one hint at a time.

1 What is special about 564 Hz for this glass?
It must match (or nearly match) the glass’s natural frequency: the frequency it rings at on its own when tapped.
2 The sound pushes on the glass 564 times a second. How does each push line up with the glass’s own vibration?
In step: each push arrives as the glass is already moving that way, so it adds energy instead of taking it away.
3 What does that do over many cycles?
Energy goes in faster than the glass loses it, so the amplitude grows large: the glass vibrates hard enough to rattle on the shelf. That is resonance.

Answer Resonance. The violin’s 564 Hz matches the wine glass’s natural frequency, so each push from the sound arrives in step with the glass’s own vibration and adds energy. Little energy is lost each cycle, so the amplitude builds up until the glass rattles on the shelf.

What the marker wanted

Achieved Names resonance (or, in (ii), gives a practical way to stop the rattle).
Merit Outlines resonance: the driving frequency matches the glass’s natural frequency, so its amplitude grows.
Excellence With (ii): a complete explanation of resonance, including a way to stop the glass rattling.

The schedule marks (d)(i) and (d)(ii) together as one item. Excellence needs this explanation of resonance together with a way to stop the rattle from (ii).

In our words, from NZQA’s 2023 marking schedule.

How did it go?

Got it moves it further out. Review brings it back tomorrow.