When light passes through a cloudy liquid, some is scattered. Here you can show that light, microwaves and radio waves can all be polarised.Įpisode 313-1: Polarisation of waves (Word, 313 KB) Demonstration: Polarisation of light by scatteringĮpisode 313-2: Polarisation by scattering (Word, 37 KB) Demonstration: Polarisation of light, microwaves and radio waves At any other angle, it is the component of the electric field perpendicular to the chains which passes through this explains why the light dims as you rotate the filters. If the polymer chains are at right angles to the electric field, the electrons cannot move very far and thus do not absorb much energy from the wave, so it passes through. (The chains are like miniature aerials, absorbing the radiation.) At the same time, the electrons re-emit the radiation in all directions, and the result is that not much radiation passes straight through. When the oscillating electric field is vertical, and the chains are vertical, the electrons are caused to move up and down with the same frequency. There are electrons that are free to run up and down the chains Polaroid is a type of plastic its molecules are long chains, oriented parallel to one another. You will have to state that light (and other electromagnetic radiations) consists of oscillating electric and magnetic fields. (Note that it is better to talk about plane-polarised waves, rather than simply polarised, as this will save confusion later.)ĭiscuss why longitudinal waves cannot be polarised.Ĭan students relate this to their observations with the Polaroid filters? Here is a simple explanation of how Polaroid filters work – use this if you think your students want a bit more explanation: The red wave is polarised in the horizontal plane, and cannot pass through. Show this diagram the blue wave is polarised in a vertical plane, and so can pass through a vertical slot. (It is helpful if the filters are rectangular rather than square, or marked in some way to help students keep track of the orientation.) Ask them to look through them at light sources (a lamp, the sky, (particularly at 90 ° to the Sun), etc.). Provide each student with two Polaroid filters. Student experiment: Using polarising filters to observe polarisation effects Student activity: Solutions may rotate polarisation (30 minutes).Student activity: Aerials and polarisation (30 minutes).Student questions: Questions on polarisation (30 minutes).Demonstration: Polarisation of light by scattering (10 minutes). Demonstration: Polarisation of light, microwaves and radio waves (30 minutes).Discussion: A simple explanation of polarisation (15 minutes).Student experiment: Using polarising filters to observe polarisation effects (5 minutes).You can establish the basic ideas using analogies. Since they cannot see either the wave nature of light or the molecular structure of Polaroid, they will have to take some of this on trust. This episode requires students to develop their idea of electromagnetic radiation. Students will learn much more about light when they study diffraction and interference. If students study these episodes before they have dealt with radioactivity, it will help them to understand the nature of gamma radiation, as well as the idea that the intensity of radiation diminishes as it spreads out. They should know the difference between transverse and longitudinal waves. They should also have studied some basic ideas about waves (how they are produced reflection and refraction). Students should know the main sub-divisions of the electromagnetic spectrum. show the inverse square law experimentally and to be able to use it in calculations.know the general properties of electromagnetic waves including the order of magnitude of the wavelength of each region and how each is detected.appreciate that polarisation of light and microwaves tell us that electromagnetic waves are transverse.understand why only transverse waves can be polarised.be able to predict what will be seen or detected with a combination of filters and different orientations of detectors and transmitters.know some of the methods by which light can be polarised.
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