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The wavelength is changing with the changing of the temperature, because the
speed of sound changes with the temperature. The air pressure is irrelevant!
| Calculation of the wavelength of radio waves and acoustic waves Calculation of the speed of sound in humid air (with air pressure) Calculation speed of sound in air and the temperature |
The formulae (formulas): c = λ × f λ = c / f = c × λ f = c / λ
| Physical value | Symbol | Unit | Formula |
| Frequency | f = 1/T | Hz = 1/s | f = c / λ |
| Wavelength | λ | m | λ = c / f |
| Time period or cycle duration |
T = 1/f | s | T = λ / c |
| Wave speed | c | m/s | c = λ × f |
| Notice: Speed of sound in air c = 343 m/s at 20 °C (68 °F) or speed of radio waves and light in a vacuum c = 299,792,458 m/s ≈ 300 000 km/s. The velocity of propagation of electric signals via copper cables is nearly 9/10 of the speed of light, which means ≈ 270,000 km/s. The velocity of propagation of electric signals via optical fibres is nearly 2/3 of the speed of light, which means ≈ 200,000 km/s. |
| It may be worth looking how different variables act on the wave. Take the wave equation (formula) y(t) = A * (sin ω t + φ) + C The A is the amplitude and represents the difference between the upper and lower peaks. The ω is the angular velocity: ω = 2 π f = 2 π / T The φ is the phase angle, the horizontal offset. The C is the vertical offset from the x-axis, usually defined as the DC offset of the waveform. |
Difference between speed and velocity
| Speed is a distance an object goes. Velocity is a measurement of speed and direction. Speed is a scalar quantity - it only has magnitude. Velocity is a vector quantity - it has both magnitude and direction. Speed is the first derivative of distance with respect to time. Velocity is the first derivative of displacement with respect to time. Speed and velocity are related in much the same way that distance and displacement are related. Speed is a scalar and velocity is a vector. |
Speed of sound in different medias
| Media | Speed of sound m/s |
| PVC soft | 80 |
| Air | 343 at 20°C |
| Cork | 500 |
| Helium | 1020 |
| Water | 1480 |
| Polystyrol | 1800 |
| Plexiglas | 1840 |
| Concrete | 3100 |
| Tile | 3600 |
| Pine wood | 3600 |
| Granite | 3950 |
| Oak wood | 4100 |
| Iron | 5000 |
| Steel | 5050 |
| Aluminium | 5200 |
| Quartz glas | 5400 |
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