The sounder in a fire alarm vibrates at a frequency of 640 Hz and produces a sound wave in the air. Some of the sound is transmitted into a concrete wall.
| Material | Speed of sound in m/s\text{m/s}m/s |
|---|---|
| air | 340 |
| concrete | 3200 |
Use the values in the table to state how the speed of the sound changes when it enters the concrete.
State the frequency of the sound in the concrete. Explain why it has this value.
The equation linking wave speed, frequency and wavelength is
v=fλv=f\lambdav=fλ
Calculate the wavelength of the sound in the concrete.