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
$wave\space speed = frequency \times wavelength$	$v = f \times \lambda$

Variable definitions

Quantity Name	Symbol	Unit Name	Unit
$wave\space speed$	$v$	$metre \space per \space second$	$m/s$
$frequency$	$f$	$hertz$	$Hz$
$wavelength$	$\lambda$	$metre$	$m$

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'.
$1 \,m$ ruler	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	$wavelength,\,\lambda$
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.

Physics; Physics practicals; KS4 Year 10; Investigating waves in different materials

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 $5\,mm$ .
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: $wave \space speed = frequency \times wavelength \\ \ \\ v = f\times \lambda$

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	$wavelength,\,\lambda$
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.

Physics; Physics practicals; KS4 Year 10; Investigating waves in different materials

1.	Clamp stand
2.	Signal generator
3.	Vibration generator
4.	String
5.	Wooden block
6.	Pulley
7.	Masses

Stationary wave formations

Physics; Physics practicals; KS4 Year 10; Investigating waves in different materials

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.