xavier catholic college physics the world communicates
XAVIER CATHOLIC COLLEGE
PHYSICS
THE WORLD COMMUNICATES
Worksheet 9: • 4.7a
Students learn to: Solve problems and analyse information using Snell’s Law
There are two types of refractive indices, absolute and relative refractive index: • •
Absolute refractive index of a medium is the ratio of the velocity of the wave in a vacuum (~air) to that of its velocity in the medium. Relative refractive index is the refractive index of the boundary of two media
The syllabus does not refer to the former but it is useful to see the connection between the two. 1. The table below shows the absolute refractive indices for various media. Medium Vacuum Air Water Ethanol Paraffin oil
Absolute refractive index 1.00 1.00 1.33 1.36 1.44
Medium Glycerol Crown glass Quartz Flint glass Diamond
Absolute refractive index 1.47 1.52 1.54 1.65 2.42
Use the information in the above table to find values for A – H in the table below. For light travelling from: Vacuum to Earth’s atmosphere Air to flint glass Air to diamond Water to air Ethanol to air Paraffin oil to glycerol Quartz to diamond Diamond to quartz W9-4.7a-Snell's Law.doc
The relative refractive index will be: A= B= C= D= E= F= G= H= Page 1 of 5
2. The path of a ray of light passing from air into glass is shown in the diagram below. Calculate:
(Shadwick; 2004: 40)
a. the relative refractive index of the boundary; b. the absolute refractive index of the glass; c. the speed of the light in the glass. 3. The path of a ray of light passing from the same glass as in the previous question into air is shown in the diagram below. Calculate:
(Shadwick; 2004: 40)
a. the relative refractive index of the boundary; b. the angle of incidence of the light.
W9-4.7a-Snell's Law.doc
Page 2 of 5
4. Which of the following diagrams illustrate a possible path of light through various media.
(Moyle et al; 1993: 102)
5. In each case use Snell’s law to find the unknown quantity.
= 1.50
(Moyle et al; 1993: 34) W9-4.7a-Snell's Law.doc
Page 3 of 5
6. The diagram shows a ray of light travelling from A to C being refracted at B.
(Shadwick; 2004: 41)
a. State whether the glass is above or below the line XY b. Calculate the absolute refractive index of the glass. c. Calculate the speed of the light in the glass. 7. The sun is actually below the horizon when it appears to be on the horizon. With the assistance of a labelled diagram, show how refraction of light by the Earth’s atmosphere can explain this.
W9-4.7a-Snell's Law.doc
Page 4 of 5
ACKNOWLEDGEMENTS Moyle, D., Allan, P. & Millar, G. (1993) A Question of Physics. Port Melbourne, Rigby Heinemann Shadwick, B. (2004) Surfing Physics The World Communicates . Marrickville, Science Press W9-4.7a-Snell's Law.doc
Page 5 of 5
PHYSICS
THE WORLD COMMUNICATES
Worksheet 9: • 4.7a
Students learn to: Solve problems and analyse information using Snell’s Law
There are two types of refractive indices, absolute and relative refractive index: • •
Absolute refractive index of a medium is the ratio of the velocity of the wave in a vacuum (~air) to that of its velocity in the medium. Relative refractive index is the refractive index of the boundary of two media
The syllabus does not refer to the former but it is useful to see the connection between the two. 1. The table below shows the absolute refractive indices for various media. Medium Vacuum Air Water Ethanol Paraffin oil
Absolute refractive index 1.00 1.00 1.33 1.36 1.44
Medium Glycerol Crown glass Quartz Flint glass Diamond
Absolute refractive index 1.47 1.52 1.54 1.65 2.42
Use the information in the above table to find values for A – H in the table below. For light travelling from: Vacuum to Earth’s atmosphere Air to flint glass Air to diamond Water to air Ethanol to air Paraffin oil to glycerol Quartz to diamond Diamond to quartz W9-4.7a-Snell's Law.doc
The relative refractive index will be: A= B= C= D= E= F= G= H= Page 1 of 5
2. The path of a ray of light passing from air into glass is shown in the diagram below. Calculate:
(Shadwick; 2004: 40)
a. the relative refractive index of the boundary; b. the absolute refractive index of the glass; c. the speed of the light in the glass. 3. The path of a ray of light passing from the same glass as in the previous question into air is shown in the diagram below. Calculate:
(Shadwick; 2004: 40)
a. the relative refractive index of the boundary; b. the angle of incidence of the light.
W9-4.7a-Snell's Law.doc
Page 2 of 5
4. Which of the following diagrams illustrate a possible path of light through various media.
(Moyle et al; 1993: 102)
5. In each case use Snell’s law to find the unknown quantity.
= 1.50
(Moyle et al; 1993: 34) W9-4.7a-Snell's Law.doc
Page 3 of 5
6. The diagram shows a ray of light travelling from A to C being refracted at B.
(Shadwick; 2004: 41)
a. State whether the glass is above or below the line XY b. Calculate the absolute refractive index of the glass. c. Calculate the speed of the light in the glass. 7. The sun is actually below the horizon when it appears to be on the horizon. With the assistance of a labelled diagram, show how refraction of light by the Earth’s atmosphere can explain this.
W9-4.7a-Snell's Law.doc
Page 4 of 5
ACKNOWLEDGEMENTS Moyle, D., Allan, P. & Millar, G. (1993) A Question of Physics. Port Melbourne, Rigby Heinemann Shadwick, B. (2004) Surfing Physics The World Communicates . Marrickville, Science Press W9-4.7a-Snell's Law.doc
Page 5 of 5
