1.  Measuring Acoustic Wavelength and Velocity Diva, Tama & Hafiz

2. Introduction Wave properties:  Wavelength ( λ ): parallel displacement in one cycle.  Amplitude ( a ): maximum perpendicular displacement.  Period ( t ): time taken for one cycle.  Frequency ( f ): cycles undergone per unit time.  Velocity ( v ): linear displacement per unit time.

3. Resonance principle  Every half a cycle, a wave reaches its amplitude.  When the amplitude of a sound wave makes contact with a physical barrier (e.g. the inside of a tube), it amplifies the sound’s intensity. This effect is called resonance.

4. Hypothesis  The relationship between velocity, wavelength and frequency is defined as v = λ f  By generating a sound wave with a constant frequency and finding its wavelength through the points of resonance, we might be able to find the speed of sound through a medium using a derivative of the above formula.

5. Materials  Biuret  Tuning forks (216 Hz, 288 Hz, 512 Hz)  Bucket  Retort stand

6. Procedure 1. Fill the biuret to the brim with tap water. 2. Tap the tuning fork on a hard surface and listen to its vibration as closely to the surface as possible. 3. Open the biuret and let the water flow out. When the water level reaches a point of resonance, the note should be momentarily amplified. 4. Rinse and repeat until no further resonance is heard.

7.  Assuming that the sound wave experiences resonance every half a cycle, l 2 – l 1 = λ /2  Where l = distance of a given resonance point from the surface.

8. Sources of error  Irregular water flow  External disturbances  Tuning fork vibration frequency not necessarily the same as the sound wave generated  Human error  False positives  Mistiming  Zero error/parallax

9. Results 216 Hz Nodistance from opening (cm) Test 1Test 2 1 10.26.0 212.39.5 315.012.6 417.116.5 522.220.2 623.1 724.6 l 2 – l 1 = 2.1 cm, 3.5 cm Calculated length: 4.2 cm, 7.0 cm Mean result: 5.6 cm Calculated velocity: 12.096 ms -1 Average difference: 3.0 cm, 3.1 cm Avg. calculated length: 6.0 cm, 6.2 cm Mean result: 6.1 cm Calculated velocity: 13.176 ms -1

10. 288 Hz Nodistance from opening (cm) Test 1Test 2 1 3.07.6 26.110.3 38.514.6 411.217.9 513.120.7 614.524.4 719.526.2 823.7 928.8 l 2 – l 1 = 3.1 cm, 2.7 cm Calculated length: 6.2 cm, 5.4 cm Mean result: 5.8 cm Calculated velocity: 16.704 ms -1 Average difference: 3.7 cm, 3.1 cm Avg. calculated length: 7.4 cm, 6.2 cm Mean result: 6.8 cm Calculated velocity: 19.584 ms -1

11. 512 Hz Nodistance from opening (cm) Test 1Test 2 1 5.916.6 210.522.3 313.028.7 415.031.6 521.034.0 623.043.7 726.0 828.3 l 2 – l 1 = 4.6 cm, 5.7 cm Calculated length: 9.2 cm, 11.4 cm Mean result: 10.3 cm Calculated velocity: 52.736 ms -1 Average difference: 3.2 cm, 5.4 cm Avg. calculated length: 6.4 cm, 10.8 cm Mean result: 8.1 cm Calculated velocity: 41.472 ms -1

12. Observation  The values calculated were much lower than the known speed of sound in air (334.2 m/s)  This might be due to the experiment method, which depends on human hearing to take readings and is therefore prone to human error.

13. Conclusion  Though the concept is sound, a more reliable method of measurement is required to achieve proper results.  Hence, this lab session is inconclusive.

14. References  Brian Arnold et al. International A/AS-Level Physics. London: Hodder Education, 2008.  “Sound Waves”. Rice University Web Services. Rice University, n.d.