Measuring Wave Properties

How many pieces of equipment are required in the practical: Measuring Wave Properties

14

list all the pieces of equipment in the practical: Measuring Wave Properties

• ripple tank

• light source

• strobe light

• metre ruler

• large sheet of paper

• stopwatch

• signal generator

• pulley

• clamp

• vibration generator

• retort stand

• string

• wooden bridge

• slotted masses with hook

purpose of ripple tank:

to create small waves in water

purpose of the light source:

to illuminate the waves to create shadows

purpose of the strobe light:

to make the waves appear stationary so that wavelength can be measured

purpose of the metre ruler:

to measure distance

purpose of the large sheet of paper:

to provide a white background to act as a screen for the wavefront shadows

purpose of the stopwatch:

to time the movement of the waves

purpose of the signal generator:

to operate the vibration generator and to measure the frequency of the stationary wave

purpose of the pulley:

to provide a smooth track to connect the horizontal string to vertical masses

purpose of the clamp:

to attach the pulley to the table

purpose of the vibration generator:

to vibrate the string

purpose of the retort stand:

to clamp the vibration generator in place to stop it moving on the table

purpose of the string:

used to observe the stationary wave

purpose of the wooden bridge:

to change the vibration length of the string

purpose of the slotted masses with hook:

to provide tension in the string

what is the resolution of the measuring equipment?

• Metre ruler = 1 mm

• Stopwatch = 0.01 s

• Signal generator ~ 10 nHz

what is the aim of experiment 1: water waves in a ripple tank

To measure frequency, wavelength and wave speed by observing water waves in a ripple tank

what is the independent variable of experiment 1: water waves in a ripple tank

Independent variable = frequency, f

what is the dependent variable of experiment 1: water waves in a ripple tank

Dependent variable = wavelength, λ

what are the control variables of experiment 1: water waves in a ripple tank

• Control variables:

  • Same depth of water

  • Same temperature of water

how many steps are there to the method of experiment 1 : Water Waves in a Ripple Tank

5

step 1 of the method of experiment 1 : Water Waves in a Ripple Tank

Set up the apparatus as shown and fill the ripple tank with water to a depth of no more than 1 cm

step 2 of the method of experiment 1 : Water Waves in a Ripple Tank

Turn on the power supply and the light source to produce a wave pattern on the screen

step 3 of the method of experiment 1 : Water Waves in a Ripple Tank

The wavelength of the waves can be determined by using a ruler to measure the length of the screen and dividing this distance by the number of wavefronts

step 4 of the method of experiment 1 : Water Waves in a Ripple Tank

The frequency can be determined by timing how long it takes for a given number of waves to pass a particular point and dividing the number of wavefronts by the time taken

step 5 of the method of experiment 1 : Water Waves in a Ripple Tank

Record the frequency and wavelength in a table and repeat the measurements

list the method of experiment 1 : Water Waves in a Ripple Tank

1. Set up the apparatus as shown and fill the ripple tank with water to a depth of no more than 1 cm

2. Turn on the power supply and the light source to produce a wave pattern on the screen

3. The wavelength of the waves can be determined by using a ruler to measure the length of the screen and dividing this distance by the number of wavefronts

4. The frequency can be determined by timing how long it takes for a given number of waves to pass a particular point and dividing the number of wavefronts by the time taken

5. Record the frequency and wavelength in a table and repeat the measurements

what variables would you include in the results table? (7)

description → time for 20 wavefronts to pass by/s → frequency/ Hz → Distance across 5 wavefronts/m → wavelength → results → average

how would you analyse the results?

determine the speed of the waves using the equation: Wave Speed = Frequency × Wavelength

v = fλ

what is the aim of Experiment 2: Investigating Waves in a Solid

To measure frequency, wavelength and wave speed by observing waves in a solid object, such as a stretched string or elastic cord

what is the independent variable of Experiment 2: Investigating Waves in a Solid

Independent variable = frequency, f

what is the dependent variable of Experiment 2: Investigating Waves in a Solid

Dependent variable = wavelength, λ

what are the control variables of Experiment 2: Investigating Waves in a Solid

• Control variables:

  • Same string

  • Same masses attached to string

  • Same length of string

how many steps are there in Experiment 2: Investigating Waves in a Solid

4

step 1: Experiment 2: Investigating Waves in a Solid

Set up the apparatus as shown, then adjust the frequency of the signal generator until a "solid" wave is produced

step 2: Experiment 2: Investigating Waves in a Solid

Once the "solid" wave is produced, record the frequency shown on the signal generator

step 3: Experiment 2: Investigating Waves in a Solid

Use a ruler to measure the wavelength, the length to measure will depend on the number of "solid" waves produced. Or measure the length of multiple wavelengths, and divide by the number of wavelengths seen

step 4: Experiment 2: Investigating Waves in a Solid

Repeat the procedure by adjusting the frequency until another "solid" wave is produced

list the method for experiment 2: Investigating Waves in a Solid

1. Set up the apparatus as shown, then adjust the frequency of the signal generator until a "solid" wave is produced

2. Once the "solid" wave is produced, record the frequency shown on the signal generator

3. Use a ruler to measure the wavelength, the length to measure will depend on the number of "solid" waves produced. Or measure the length of multiple wavelengths, and divide by the number of wavelengths seen

4. Repeat the procedure by adjusting the frequency until another "solid" wave is produced

what variables would you include in a results table of Experiment 2: Investigating Waves in a Solid

description → first frequency/Hz → wavelength/m → second frequency/Hz → wavelength/m → third frequency / Hz → wavelength → results → average

how would you analyse the results of Experiment 2: Investigating Waves in a Solid

• The speed of each wave can be determined using the equation:

Wave Speed = Frequency × Wavelength

v = fλ

identify and rectify the systematic errors that could happen in the experiments (3)

• It can be difficult to identify the wavefronts while they are moving

  • Use a stroboscope (flashing light) matched to the same frequency of the waves, this will be indicated by the waves appearing to not be moving

  • The frequency can be read from the frequency setting of the stroboscope, and the wavelength will be easier to determine while the waves appear still

rectify 3 of the the random errors that could happen in the experiments (3)

• To improve the accuracy of the wavelength measurement in the ripple tank:

  • Measure across a number of waves (e.g. 5 of them) and then divide the distance by the number of waves

• To improve the accuracy of the frequency measurement in the ripple tank:

  • Measure across a longer time period (e.g. a minute) and then divide the number of waves by the time

• When taking repeat measurements of the frequency of the "solid" wave, the best procedure is as follows:

  • Determine the frequency of the "solid" wave when the largest vibration is observed and note down the frequency at this point

  • Increase the frequency and then gradually reduce it until the "solid" wave is clearly observed again and note down the frequency of this

  • If taking three repeat readings, repeat this procedure again

  • Average the three readings and move on to the next measurement

list 3 of the safety considerations that must be taken in this experiment

• Care should be taken when working with water and electricity in close proximity

  • Carelessness could lead to electric shock

• No food or drink should be consumed near the experiment 

• If using strobe lighting to see the wavefronts more clearly, ensure no one in the room has photosensitive epilepsy

• Make sure to stand up during the whole experiment, to react quickly to any spills

• Use a rubber string instead of a metal wire, in case it snaps under tension

• Wear safety goggles to protect the eyes in case the string or cord snaps

• Stand well away from the masses in case they fall onto the floor

  • Place a crash mat or any soft surface under the masses to break their fall