Speed of light in glass = 1.9 × 108 m s–1, speed of light in vacuum = 3 × 108 m s–1
1. A cat sees a goldfi sh in a fi shbowl and lunges at it with its paw. Explain why the cat may strike above where the fi sh actually is.
2. A diagram on a page is viewed through a transparent block 4 cm thick. The diagram appears to be 1.5 cm closer than the page actually is. Calculate the refractive index of the block.
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3. How much faster is light travelling through glass of refractive index 1.6 than diamond of refractive index 2.53?
4. If a student calculated the refractive index of glass to be 1.53, what is the percentage error if she uses the speed of light to verify this?
CHAPTER 14 EXERCISE 14C
1. Give a reason as to why a diamond sparkles more than glass.
2. What is the critical angle of a piece of glass of refractive index 1.44?
3. If the critical angle for a material is 52°, what is its refractive index?
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4. If the refractive index of a certain plastic is 1.25, calculate the critical angle between the plastic and a vacuum.
CHAPTER 14 EXERCISE 14D
1. Give two reasons as to why optical fi bres are preferable to copper in information transfer.
2. Explain with the aid of a labelled diagram how an optical fi bre transmits light.
3. If the refractive index of an optical fi bre core is 1.35, what is the minimum angle required for total internal refl ection?
4. If the core of an optical fi bre has a refractive index of 1.57, how long will it take to send a light pulse 10 km?
5. Explain why an optical fi bre has a less dense cladding around its core.
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6. Draw a diagram showing the path of a ray of light travelling through an optical fi bre.
7. What is the minimum refractive index required for a 45°–90°–45° prism to turn light through 90°?
8. A swimmer is 2 m underwater. When they look up, they notice that they can see the bottom of the pool refl ected in the water but a circle of water is transparent. What is the name given to this eff ect? If the refractive index of the water is 1.33, what area of water is transparent to the swimmer, at this depth?
