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## National STEM Learning Centre

Skip to 0 minutes and 1 second [Ripple tank] Here we can see a ripple tank which is currently needed for one of the practical’s at GCSE. You may have one tucked away somewhere in your department, which more than likely leaks. In this video we will look at how to use it, and how to make cheaper alternatives if required. To generate the waves it’s best to use a signal generator with a digital display, so students can read it easily. It’s then connected up to a vibration generator which is used to create the waves.

Skip to 0 minutes and 42 seconds Alternatively, you can connect a motor up with a piece of plastic offset to create the motion of waves. You then connect this up to a power pack motor which connects to a variable resistor. You use this to adjust the current which will either speed up or slow down the rotation of the motor. This will not give you a read out frequency but will still give you the desired effect. The faster the motor turns the more waves you get.

Skip to 1 minute and 14 seconds If you have a ripple tank in your school then it would probably look like this. By placing a motor on to it you can then project an image onto some paper below so you are able to take the measurements you need. Here is a cheaper alternative that can be made easily. Just use a clear dish with some water in it, place your motor on the surface and use an OHP to project the image onto the wall which students will find easier to see. From their earlier calculations of speed equals distance over time, students should be able to link this to wave speed and realise it is the same.

Skip to 1 minute and 49 seconds Get them to think about what else they can work out, in this case, they can estimate the wavelength or measure it if possible. One way of doing this is to have a ruler placed on the bottom of the dish and take a picture with their phones to get a better answer. Try not to give students the equation of wave speed is frequency times wavelength. This is a common issue in physics, we give them a linear equation and then ask them to prove it, as if it has never been proven before and that will switch them off. See if they can figure it out for themselves, as it will help them understand the relationship better.

# Ripple tank

In the video above, you have just seen how the ripple tank can be used in the teaching of waves. The ripple tank tends to be a piece of equipment that has been placed away in some schools and hasn’t been used for some time. This is unfortunate as it is a really useful tool to teach many properties of waves and also allows you to show students how waves interact with matter. With most waves such as radio or X-rays invisible to the naked eye, this equipment allows you to demonstrate visually what often is invisible such as constructive and destructive interference.

Here we show you two methods, one using an actual ripple tank with the image projected onto the desk below, as well as a cheaper option using a glass dish and an overhead projector. As this is currently a required practical at GCSE in England with most exam boards and will be something that can be assessed in exams, it is important that students are able to access this.

Think about what equipment you have at your school and how you could use it in your lessons.