## Chapter Objectives and Summaries

### CHAPTER 18 Refraction

LEARNING OBJECTIVES
Knowledge of subject matter
• Explain what the term 'refraction' means.
• Give examples of effects that show the refraction of light.
• Explain what a spectrum is and how it is formed.
• Define 'refractive index' and use it to solve problems.
• Explain what is meant by total internal reflection and critical angle. Give examples of total internal reflection.
• Distinguish between real and apparent depth in water.
• Explain how optical fibres works.
• Explain colour addition and say how a colour television set works.

SCIENTIFIC PROCESSES

• Draw diagrams to show the passage of light through rectangular and semicircular blocks and a prism.
• Write up an experimental report on Snell's law
• Discuss applications of optical fibres.

COMPLEX REASONING PROCESSES

• Critically discuss the use of total internal reflection in modern and future technology eg. Optical fibres
• Solve complex and/or novel problems on real and apparent depth and refraction.

### CHAPTER 18 SUMMARY

• Refraction is the bending of light as it travels from one medium to another.
• Light travels at a slower speed in a more optically dense medium.
• Snell's law states that when light travels from one medium to another the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the refractive index `n'.
Sin (i)/Sin (r) = n
• The ratio of the speed of light in two media is equal to the relative refractive index of the media n12 = v1 /v2
• The absolute refractive index is obtained when light travels from air to another medium.
• The relative refractive index is obtained when light passes from one medium to another and is given by the formula:
n12 =n1/n2
• In general for light passing from medium 1 to medium 2:
n1 sin q1 = n2 sin q2.
Also n12 = f1/f2 = l1/l2 = n2/n1
• Total internal reflection occurs when light goes from a more optically dense to a less optically dense medium.
• The critical angle is the angle of incidence in a material that produces an angle of refraction of 90o in air (or the less dense medium).
• For total internal reflection sin qc = 1 / n where qc is the critical angle and n is the relative refractive index.
• The relationship between apparent and true depth is given by the formula:
n = true depth/apparent depth
• Mirages and rainbows can be explained by refraction and total internal reflection.
• Refraction and total internal reflection is used in binoculars, `cat's eyes' on roads, bicycle reflectors, and optical fibres technology applications.