A cathode-ray oscilloscope (c.r.o.) is used to present the trace of a sound wave. The time-base is set at $5\,\mu\text{s mm}^{-1}$. What frequency does the sound wave have?
- A$6.7\,\text{Hz}$
- B$67\,\text{Hz}$
- C$6.7\,\text{kHz}$
- D$67\,\text{kHz}$
Physics 9702 · AS & A Level · Practical circuits