Unit: Waves
Year: 1997 Question#: 42
Question: The diagram below shows a ray of monochromatic light incident on an alcohol-flint glass interface. What occurs as the light travels from alcohol into flint glass?
(1 ) The speed of the light decreases and the ray bends toward the normal.
(2 ) The speed of the light decreases and the ray bends away from the normal.
(3 ) The speed of the light increases and the ray bends toward the normal.
(4 ) The speed of the light increases and the ray bends away from the normal.
What is this question really asking?
Explanation by: Becky G
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Answer 1
The speed of the light decreases and the ray bends toward the normal.
CORRECT
By looking at the reference table you find that flint glass has a value of 1.61 while alcohol has a value of 1.36, indicating that flint glass is the slower medium. As the light ray enters a slower medium, the ray bends toward the normal. The slower the medium, the closer the ray will get to the normal. return to top
Answer 2
The speed of light decreases and the ray bends away from the medium.
INCORRECT
As the speed of light decreases, the ray would not bend away from the normal. The ray would only bend away from the normal if the medium was faster than the previous one. Which it is not.
Try checking the reference table you'll find that flint glass has a value of 1.61 while alcohol has a value of 1.36, indicating that flint glass is the slower medium. return to top
Answer 3
The speed of light increases and the ray bends toward the normal.
INCORRECT
The speed of light increasing would make the ray bend away from the normal, not toward the normal. The speed of the light also decreases as it passes from the alcohol to the flint glass. Try looking at the reference table you'll find that flint glass has a value of 1.61 while alcohol has a value of 1.36, indicating that flint glass is the slower medium. return to top
Answer 4
The speed of light increases and the ray bends away from the normal.
INCORRECT
The speed of light does increase as the ray bends away from the normal, but not in this picture. The speed of light decreases rather than increases and that makes the ray bend toward the normal. Try looking at the reference table, you'll find that flint glass has a value of 1.61 while alcohol has a value of 1.36, indicating that flint glass is the slower medium. return to top
What's this question really asking?
Can you use a reference table to find the index of refraction and then use that data to predict the refraction? return to top
