An ultrasonic level sensor sends a pulse through a polymer window and into oil. The crystal in the sensor completes 18 000 18\,000\,18000 oscillations in 0.60 s.
| Medium | Speed of sound in m/s\mathrm{m/s}m/s |
|---|---|
| Polymer | 2400 |
| Oil | 1350 |
Calculate the decrease in wavelength when the pulse passes from the polymer into the oil.