Which one of the following is the natural phenomenon based on which a simple periscope works?
- A.Reflection of light
- B.Refraction of light
- C.Dispersion of light
- D.Total internal reflection of light
Correct answer
Explanation
The correct answer is A, Reflection of light. A simple periscope has two plane mirrors, and light reaches the eye only by bouncing off them.
In a simple periscope, two plane mirrors are fixed parallel to each other at the two bends of a long tube, each tilted at 45° to its length. Light from an object enters the upper opening, strikes the first mirror, turns through 90° and travels down the tube, then strikes the second mirror and turns again towards the eye. This lets a viewer see over a wall or crowd, or out of a trench or submarine, while staying hidden. The laws of reflection, angle of incidence equal to angle of reflection, explain the whole device.
B is wrong because refraction, the bending of light between two media, is the basis of lenses, not of a mirror periscope.
C is wrong because dispersion is the splitting of white light into colours, as in a prism or a rainbow.
D is wrong because total internal reflection is used in optical fibres and in prism-based instruments, not in the simple mirror periscope.
Exam tip: periscope, two plane mirrors at 45°; optical fibre, total internal reflection.
Practice Questions
View allWhich one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
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- C.between 2 kHz and 20 kHz
- D.greater than 20 kHz
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- B.Potassium
- C.Calcium
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Read the full explanation →Which of the following sets of elements has the same valency?
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- B.Na, Mg, Al
- C.Mg, Ca, K
- D.Mg, Ca, Ba
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