Hello, and welcome. My name is Sarah Dix. I'm a physics teacher here at Reddam House
School. Today, we are going to be looking at the core practical, investigating waves,
so you can obtain accurate results in your own experiment.
The first experiment we will be looking at is investigating waves in water. You'll be
measuring the speed, frequency, and wavelength of a waterway using a ripple tank. To carry
out this experiment, you will need the following, ripple tank, stopwatch, ruler, digital camera
or smartphone.
Firstly, set up a ripple tank with a straight dipper parallel to one of the shorts sides
of the tank. This allows you a longer length so you have the ability to measure more waves.
Next, place a ruler to one of the long sides of the paper below the tank so you can see
the markings. This is so you can easily measure the waves.
Then, you will need to vary the current to the motor. You will know when it's set to
the correct current as the waves will be easy to count. Using your smartphone or stopwatch,
film and then count how many waves are formed in 10 seconds. Using your camera's slow motion
function, record this number into a suitable results table.
We now need to measure the wavelength of water waves. To do this, look at the waves against
the ruler. We can look at the markings on the ruler to estimate the wavelength of the
waves. To get a more accurate result, you could use a smartphone camera to take a photo
of the waves on the ruler on the paper.
To measure the wave, mark two points on the edge of the paper below the ripple tank. This
will be the starting and finishing points. Now measure the distance between them.
You now need to get your stopwatch and smartphone. Using the slow motion function, time how long
it takes away to go from start to the finish mark. Make a note of this time. Ensure all
of your data is in an appropriate results table, remembering to add the correct units
to the headings.
To work out the speed of a single wave, divide the distance, which in this case is the length
of the wave by the time taken for the wave to pass one point to the next. Next, we need
to find the frequency of the waves. To do this, we take the number of waves in 10 seconds
and divide by 10.
So if we counted five waves, we would divide 5 by 10, and the frequency would equal 0.5
Hertz. Finally, we need to calculate the speed of the series of waves. We do this by multiplying
the wavelength as a wave that we measured earlier by the frequency you have just worked
out.
For the second part of this core practical, we will be measuring waves in a solid. Our
aim is to determine the speed of sound in a solid. To carry out this experiment, you
will need the following, two clamps and stands, two rubber bands, a long metal rod up to a
meter long, and meter rule, a hammer, a smartphone with a suitable frequency app.
Firstly, you need to suspend a metal rod horizontally using a clamp stand and rubber bands. Make
sure you balance the water over the feet of the clamp stand. This makes the apparatus
stable and less likely to tip over.
You now need to measure the speed of sound in the bar. We do this by hitting one end
of the rod with a hammer. At the same time, hold your smartphone with a frequency app
near the rod. And then note down the peak frequency.
Finally, you need to measure the length of the rod with your meter rule. Doubling this
value will give you the wavelength. We calculate the speed of sound in a metal rod by multiplying
the frequency by the wavelength. Using the equation shown, your teacher may now provide
you with further questions to help you reflect on the activities you have carried out during
this core practical.