Investigating waves in different materials
In a nutshell
By using a wave source, you will investigate and measure the wave speed, frequency and wavelength of a wave in a liquid or a solid. You will do this by conducting two different experiments. First using a ripple tank in water, and then using a stretched string.
Equations
The equation is the one being evaluated in this experiment.
Word Equation | Symbol Equation |
wave speed=frequency×wavelength | v=f×λ |
Variable definitions
Quantity Name | Symbol | Unit Name | Unit |
wave speed | | metre per second | |
frequency | | | |
wavelength | | | |
Equipment list
The following equipment list can be used to conduct the experiment to measure the wave speed, frequency and wavelength of a wave.
Equipment | Use |
Ripple tank | To generate waves in the water using a dipper to produce vibrations. |
Light source | To illuminate the waves onto the floor below. |
Strobe light | To make the waves appear 'frozen'. |
| To measure distances. |
Large sheet of paper | To act as a screen to view the wavefronts on. |
Stopwatch | To time the waves. |
String | To model waves in a solid. |
Signal generator | To generate vibrations that produce waves. Also used to measure the frequency of a wave. |
Masses (with hook) | The provide tension in the string. |
Pulley | To connect the string (oriented horizontally) to the masses (vertical). |
Clamp | To attach the pulley system to the table. |
Vibration generator | To generate vibrations of the string. |
Retort stand | To clamp the vibration generator in place. |
Wooden bridge | To change the length of the string that vibrates. |
Experiment 1: Measuring the wave speed, frequency and wavelength of waves produced by a ripple tank
Experimental variables
The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The control variables are the variables that are kept constant.
Independent Variable | frequency,f |
Dependent Variable | wavelength,λ |
Control Variables | Depth of water, temperature of water |
Safety precautions
When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.
Hazard | Risk | Safety Measure |
Power supply and water | Working with electricity and water could lead to electric shock if not careful. | The wiring should be treated carefully. |
Strobe lighting | Could cause epileptic seizure. | Ensure no one has photosensitive epilepsy. |
Method
These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.
| 1. | Support | 2. | Power supply | 3. | Dipper | 4. | Light source | 5. | Water | 6. | Wavefronts | 7. | Paper | 8. | Ruler | |
1. | Set up the apparatus as shown in the diagram. The straight dipper should be on one side of the tank. A ruler should be placed adjacent to the screen. Fill the ripple tank with water to a depth of 5mm. |
2. | Switch on the power supply and light source. A wave pattern should be produced on the screen below the tank. |
3. | Measure the wavelength by using the ruler to measure the length between an amount of wavelengths. To find one wavelength, divide the distance measured by the number of wavelengths. Tip: If you struggle to measure the distance, take a picture of the wavefronts and a ruler. Then measure the wavelength using the photo! |
4. | Measure the frequency by timing how long it takes for ten waves to pass a certain point on the ruler. Then divide the ten wave fronts by the time it took to find the frequency of the waves. |
Analysis
This is how you will use the data recorded to form conclusions.
1. | Work out the wave speed by using the wave speed equation:
wave speed=frequency×wavelength v=f×λ |
Conclusion
The result of your experiment should show how wave speed, frequency and wavelength are related. The wave speed should tell you how fast a water wave of a certain frequency and wavelength travels.
Evaluation
Once you have completed your experiment, it is important to consider how it could be improved. You should come up with ways to improve the speed of the wave. If you got a result that seems unreasonable, think about why this was.
Experiment 2: Measuring the wave speed, frequency and wavelength of waves on a string.
Experimental variables
The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The constant variables are the variables that are kept constant.
Independent Variable | frequency,f |
Dependent Variable | wavelength,λ |
Control Variables | String, length of string, masses attached to string |
Safety precautions
When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.
Hazard | Risk | Safety Measure |
Weights | Weights may become loose and fall on feet. | Don't stand directly beneath the weights. Place a matt under the masses to reduce their impact. |
String | A stretched string may snap. | Use a rubber string instead of a metal wire. Wear safety goggles to protect eyes. |
Method
The method is similar to the previous part, however there are slightly different procedures for measuring the variables.
| 1. | Clamp stand
| 2.
| Signal generator
| 3.
| Vibration generator
| 4.
| String
| 5.
| Wooden block
| 6.
| Pulley
| 7.
| Masses
|
|
Stationary wave formations
1. | Set up the apparatus as shown in the diagram. |
2. | Turn on the signal generator and adjust the frequency until a stationary wave is shown. This frequency depends on the length of the string used and the masses on the pulley. |
3. | Record the frequency shown on the signal generator - this is the frequency of the wave. |
4. | Measure the wavelength by measuring the length of multiple wavelengths, and divide by the number of wavelengths measured. Tip: You may only be able to see half a wavelength. Measure this and divide by 0.5 to find the value of one wavelength. |
5. | Adjust the frequency until another stationary wave can be observed. Repeat steps 3 and 4 for this wave. Repeat this for another stationary wave to get three sets of measurements. |
Analysis
Repeat the same analysis as experiment one, but find a wave speed for each stationary wave.
Conclusion
The results of this experiment should find that although the frequency and wavelength changes for each stationary wave, the wave speed stays the same.
Evaluation
Perform the same evaluation as experiment one on your data. Make sure you come up with improvements to the experiment and explain the reasons behind any anomalous results.