Class 12 Physics · Chapter 3 · Test 3
Thin Films and Gratings
38 MCQs
37 questions · 30 min · 37 marks
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Sample questions
The first 5 of 37. Try each one, then tap to see the answer.
Question 1
Colours seen on a thin layer of oil floating on water are due to:
- AReflection only
- BInterference of light reflected from the front and back surfaces of the film
- CRefraction only
- DAbsorption of light
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Answer: B
Light reflected from the upper and lower surfaces of the film interferes.
Question 2
Different colours appear in a thin film because:
- AInterference may be constructive for some wavelengths and destructive for others
- BAll wavelengths interfere constructively
- CLight has no wavelength
- DThe film has no thickness
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Answer: A
Colours differ in wavelength so the condition for reinforcement is met by different colours at different places.
Question 3
In an air wedge between two glass plates the path difference between the two reflected waves is:
- At
- Bt/2
- C2t
- D4t
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Answer: C
The path difference is twice the thickness t of the air wedge.
Question 4
Along the line where two glass plates of an air wedge are in contact one observes:
- AA bright fringe
- BA dark fringe
- CA coloured fringe
- DNo fringe
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Answer: B
A half cycle phase shift on reflection makes the contact line dark instead of bright.
Question 5
The half cycle phase shift on reflection can be predicted from:
- ANewton's laws
- BMaxwell's equations and the electromagnetic nature of light
- CHooke's law
- DBoyle's law
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Answer: B
The text states the phase shift can be predicted from Maxwell's equations.
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