In order for an observer to see a mirage on a hot day, total internal reflection must occur - Leaving Cert Physics - Question b - 2022
Question b
In order for an observer to see a mirage on a hot day, total internal reflection must occur. Mirages happen when the ground is very hot and the hot air just above th... show full transcript
Worked Solution & Example Answer:In order for an observer to see a mirage on a hot day, total internal reflection must occur - Leaving Cert Physics - Question b - 2022
Step 1
Describe an experiment to demonstrate total internal reflection.
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Answer
To demonstrate total internal reflection, the following apparatus can be used:
Apparatus
A ray box (or laser) to produce a beam of light.
A semi-circular glass block.
Method
Place the semi-circular glass block on a flat surface.
Shine a light ray into the flat surface of the block at an angle greater than the critical angle.
Adjust the angle and observe that the light is reflected back into the block instead of refracting out into the air.
Observation
The observer will see that the light ray does not exit the glass but reflects entirely within it, hence demonstrating total internal reflection.
Step 2
If the light from a distant object comes to focus in front of the retina, the person will see a blurred image. This person is said to be short sighted. What type of lens is used to correct short sightedness?
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Answer
The type of lens used to correct short sightedness is a concave lens, also known as a diverging lens. This lens spreads out the light rays, allowing them to focus further back on the retina, thus clarifying the image.
Step 3
Calculate the power of the combination of the eye and the lens.
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Answer
The power of the combination of the eye and the lens can be calculated using the formula:
P=Peye+Plens
Where:
Peye=62m−1
Plens=−2m−1
Substituting the values:
P=62+(−2)=60m−1
Thus, the power of the combination is 60 m⁻¹.
Step 4
Calculate the focal length of the lens in the glasses.
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Answer
The focal length of a lens can be calculated from its power using the formula:
f=P1
Where:
P=−2m−1 for the lens in the glasses.
Substituting the values:
f=−21=−0.5m
Thus, the focal length of the lens in the glasses is -0.5 m.
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