P6 Experiments with Waves (page 219) Flashcards
What equipment do you use to find the wavelength of the sound waves generated?
By attaching a signal generator to a speaker you can generate sounds with a specific frequency.
You can use two microphones and an oscilloscope to find the wavelength of the spimd waves generated.
What is the process of measuring wavelengths of sound?
1) Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
2) Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display, but have moved exactly one wavelength (λ)
3) Measure the distance between the microphones to find one wavelength (λ)
4) You can then use the formula v = fλ (p.218) to find the speed (v) of the sound waves passing through the air - the frequency (f) is whatever you set the signal generator to (around 1 kHz is sensible).
5) The speed of sound in air is around 330 m/s, so check your results roughly agree with this.
How do you measure the speed of water ripples?
by using aripple tank. (see page 219 diagram)
How can you create water waves at a set frequency?
by using a signal generator attached to the dipper of a ripple tank.
In a practical experiment measuring speed of water ripples, if you dim the lights in the lab and turn on the lamp, what will you see?
you should see the wave crests as shadows on the screen below the tank.
The distance between each shadow line is equal to one wavelength.
How do you measure the distance between shadow lines that are 10 wavelengths apart?
you divide this distance (10 wavelengths), by 10 to find the average wavelength.
(this is a good method for measuring the wavelength of moving waves (p.233) or small wavelengths.
what formula do you use to calculate the wave speed of the waves?
v = fλ
Why is the ripple tank experiment suitable for investigating waves?
this set-up is suitable because it allows you to measure the wavelength without disturbing the waves.
You can use the Wave Equation for Waves on Strings. what is the process?
1) set up the equipment as shown on diagram 3 page 219, then turn on the signal generator and vibration transducer. The string will start to vibrate.
2) Adjust the frequency of the signal generator until there’s a clear wave on the string. The frequency you need will depend on the length of string between the pulley and the transducer, and the masses you need.
3) You need to measure the wavelength of these waves. The best way to do this accurately is to measure the lengths of, say four or five half-wavelengths (as many as you can) in one go, then divide to get the mean half-wavelength (p.6). You can then double this mean to get a full wavelength. (see diagram 4 on page 219).
4) The Frequency of the wave is whatever the signal generator is set to.
(you can find the speed of the wave using v = fλ/
(this set-up is suitable for investigating waves on a string because it’s easy to see and measure the wavelength (and frequency).
Why are sound waves, rupples, and waves on strings used as model waves?
because they’re easy to work with.
Describe a suitable experiment to measure the wavelength of a water wave (3 marks)
E.g. attach a signal generator to a dipper and place it in a ripple tank filled with water to create some waves (1 mark). Place a screen underneath the ripple tank, then turn on a lamp above the ripple tank and dim the other lights in the room (1 mark). Measure the distance between shaddow lines that are 10 wavelengths apart on the screen beneath the tank, then diide this number by 10 - this is equal to the wavelength of the ripples (1 mark).
