Transcription
So we've discussed the strong force and the weak force, which may not be as familiar to you as the electromagnetic force. Hopefully, you've come across this in some way, shape, or form, and this talk is just going to cement some of that knowledge and show you how we use the electromagnetic force in Radiology Physics.
So, the electromagnetic force describes either the force of attraction between two oppositely charged ions or the force of repulsion between two similarly charged ions. Here, we've got two positive ions that are repelling one another, but it could also be two negative ions. Secondly, opposite magnetic fields also attract one another, and like magnetic fields repel one another. The difference with a magnet is that they exist in dipoles, and charges or ions exist in discrete entities from one another, but the same force is occurring between the two. Opposites attract, and like charges repel.
So, we can use this electromagnetic phenomenon to our advantage. Firstly, by moving a magnet through a conductive coil, the movement of this magnet will then induce a current within the coil. So, the movement of magnetism induces a current, and the opposite is also true. If we were to run a current through this wire, that would induce a magnetic field, and it's these two phenomena that we manipulate over and over again in our Radiology Physics course to create the images that we are trying to create. In MRI, we can manipulate the current running through these coils in order to change the magnetic field that will eventually interact with matter and create our MRI signal that we'll detect and create our MRI image.
So, let's go through a couple of examples just in our x-ray physics module where the electromagnetic force comes in. Here, we've already described the binding energy of an electron is due to the electromagnetic force between that negative electron and that positive proton. That force of attraction that's keeping that electron within its orbit.
Next, we can use the electromagnetic force in our x-ray circuit when we are trying to up the voltage of our wall current and our x-ray tube current. This is what's known as a step-up transformer. The current running through this first coil changes rapidly backwards and forwards; it's alternating current. That change in current then creates a magnetic field that switches back and forth, and that magnetic field interacts with the secondary coil, which then, the movement of that magnetic field, induces a current in that coil. We're utilizing the electromagnetic effect to up the voltage within our circuit.
When we look at electromagnetic radiation, which will be our next talk, we will see that the electromagnetic wave is two orthogonal waves. One wave is an electric wave running perpendicular to a magnetic wave. The movement of the electric wave induces magnetism, and the movement of the magnetic wave induces the electric wave. You can see that this is a self-propagating wave. The electromagnetic force, the movement of current induces magnetism, the movement of magnetism induces currents, and because it's self-propagating, this wave can travel through a vacuum; it doesn't require a medium to propagate.
And lastly, when we look at our x-ray tube, we accelerate electrons away from our cathode. We've produced electrons through the process of thermionic emission. We accelerate these negative electrons away from our negative cathode towards our positive anode. That force of attraction between negative electrons and a positive anode. And we can even steer that electron beam by making this focusing cup within our cathode negatively charged, repelling those electrons away, shaping them towards our anode. And these are all concepts that we're going to cover in a lot of detail during our x-ray physics module.
Now, if you like this style of teaching, I have collated over 10 years of past papers, and I go through each and every question with you, showing you exactly how I would answer that question, as well as talking about the various different concepts that are brought up in those questions. So, if you're studying for your exams, I'd highly recommend checking that out. Otherwise, I'll see you on our next talk where we are going to talk about electromagnetic radiation, leading on into our x-ray physics module. I'll see you there. Goodbye.