Dispersion By A Prism.ppt 6b193g

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.

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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

What happens to the ray of light? It is (mainly) reflected or

away refracted ? from the normal

or

towards the normal

But different colours are refracted by different angles.

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

R What happens now? Red is deviatedleast most / least ? Violet is deviatedmost most / least ?

scree n

V

R There is a spectrum scree n

on the screen: Red Orange Yellow Green Blue Indigo Violet

ROY G BIV

V

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

wavelength

violet red 7 mm 10 000

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

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