Teacher’s Notes This sequence of slides is designed to introduce, and explain dispersion by a prism to produce a spectrum, as explained on page 206 in New GCSE Physics for You, 2006 & 2011 editions. (or page 216 in GCSE Physics for You, 2001 edition). Note : When you start this PowerPoint if you see a message about “Read-only embedded fonts” then you are recommended to select “Open Read-Only” as this (i) gives a clearer font for those at the back of the room and (ii) ensures that the text-highlighting of key words is correct. On each slide the key points are revealed step by step, at the click of your mouse (or the press of a key such as the space-bar). Before making the next mouse-click you can ask questions of the class or make statements about what is about to be revealed. This should help students to become clearer about the ideas involved. Naturally it pays to have quick practice-run first. To start the slide-show, press function-key F5 (or right-click->Full Screen) (to return to ‘normal view’ press the <Esc> key). For more (free) PowerPoint presentations, visit www.physics4u.co.uk

New Physics for You, pages 206 - 207 Dispersion by a prism New Physics for You, pages 206 - 207

Learning Objectives You should learn : How a light ray is deviated by a prism, How white light is dispersed by a prism, The colours of a white light spectrum, About the wavelengths of different colours.

Here is a glass prism: A ray of white light arrives

away from or towards the normal the normal What happens to the ray of light? It is (mainly) reflected or refracted ? away from or towards the normal the normal But different colours are refracted by different angles.

devi ated In fact, the ray is : (bent through an angle), and dispersed (split up into separate colours) like this.

Red is deviated most / least ? least screen What happens now? Red is deviated most / least ? least Violet is deviated most / least ? most

There is a spectrum on the screen: V screen There is a spectrum on the screen: Red Orange Yellow Green Blue Indigo Violet ROY G BIV

What is the real difference between red and violet light ? 4 10 000 mm wavelength violet red 7 10 000 mm

Learning Outcomes You should now: Understand what happens when white light enters a prism, Distinguish between deviation and dispersion, Know the colours of the spectrum, in order, Understand the connection between colour and wavelength.

For more details, see: New Physics for You, page 206 - 207 For more free PowerPoints, visit the web-site at www.physics4u.co.uk

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