# Year 12 - Physics

 The Virtual Ripple Tank:  Waves in a ripple tank are 2-dimensional waves as opposed to the waves that we examined in the springs which are described as one dimensional waves.  In this activity it is intended that you will review the properties of these waves using a ripple tank simulation.  You will then extend this to examine some of the phenomena that we will be investigating in more detail over the coming weeks.  The virtual ripple tank can be found by clicking on the graphic below.  Tthe simulation was devised by Harvard University. The first task is to become familiar with the Virtual Ripple Tank When the applet starts up you will see a blue circle (called the "source") emitting red and green circular waves. The green areas are positive and the red areas are negative. If you prefer to think of the waves as sound waves, the green areas would be areas of high pressure, and the red areas would be low pressure. The source might be a speaker of some sort. Activity 1:  Single Source One Frequency You may find that the Simulation Speed and other settings need some adjustment when the applet opens.  This is essentially a matter of trial and error.  .The applet opens the source is described as a James Resonator.    Change this to the Single Source setting.  See below for details. Initially have the other settings as shown below. Move the source using the mouse to the centre of the screen.  Note you may notice that although we are producing circular waves true circles are not apparent.  This appears to be related to the computer screen.  Just ignore the slight distortion if any exists. Clear the screen by choosing the Clear Waves option from the dropdown Actions menu. Uncheck the check box and observe the result.  Now check the button.  Now you can observe the wave motion in three dimensions. Clicking and dragging with the mouse on the 3D image will change the orientation of the image. From the Probes menu choose the 4 Probes option These probes may now be placed at various positions on the screen.  Unfortunately the amplitude of the wave they generate will auto fit to the space on the screen, so you will not be able to judge the impact of the distance from the source and how energy is lost as the wave propagates.  However, the probes will show any phase differences that exist in different parts of the screen.  If you stop the motion then dragging a probe will show this change in amplitude with distance from the origin. With the probes set out as follows you should be able to observe something with respect to the frequency of the wave motion as the waves propagate from the centre.  See diagram below. Activity 2: Reflection To set up the tank to show reflection.  Use the following settings. Draw a line starting from the left hand edge at an angle of about 45 degrees.  Start the simulation.  Look carefully at the results.  You may find that you have to adjust settings to obtain the best image. A better reflection effect can be demonstrated using the following settings. Now you will need to draw a linear wall using the mouse.  See diagram below.    Activity 3: Refraction 1 Use the following settings. Place the probes in the two different regions.  Notice the different speeds of each wave train.  Also observe the frequency of the waves in each region. Activity 4: Refraction 2 Use the following settings.  However also you will need to increase the frequency to about 12 to 15.  This shows excellent refraction effects as well as reflection effects.  Arrange probed at appropriate positions to investigate alterations, if any in frequency.  Clicking the mouse over the graphing area will stop the simulation and consequently allow a refreshed trace to appear. Diffraction and Interference Phenomenon: This is the prime focus of our work at present.  These exercises will give you some insight into the effects that are able to be observed both with sound and with light.   Diffraction:  Diffraction occurs when a wave passes through a narrow opening or slit.  It also occurs when when waves pass by an obstacle.  The wave will essentially bend around the barrier.  Work through Experiment 5.3 - Diffraction of Water Waves.  You will note that the blocks have a rather interesting tapered shape.   These can actually be drawn on the simulation.  You can investigate the effect of this tapering in comparison to an untapered situation.    Interference: Interference will occur whenever there are two coherent wave sources producing waves of identical frequency.  This can occur with sound or with light.  Work through Experiment 5.4 - Interference of Water Waves.  The simulation already has a a preset feature the two point sources, see below Also the single slit, double slit and triple slit are available as presets. A classic sound interference effect is the interference produced by a tuning fork.   This can be modelled in this simulated ripple tank by using the Linear Quadrupole simulation.  Look at the simulation and predict what effect you should be able to note with the tuning fork. You should also examine the preset experiment on Beats.  Look carefully at the set up in terms of the phases of the sources and the differences in the frequencies of each source.  Each source has an adjustable frequency.  Look carefully at the probe.  Look at the graph that is being generated.  Predict what you might hear if these were sound waves.  Copies of the sheet that explains each of the possible settings on the simulation are available.