Periscope And Kaleidoscope

We know that plane mirror reflects light falling on it. This reflected ray can act as incident ray for another mirror. This process of reflection of light several times between reflecting surfaces is known as Multiple reflection of light.

Multiple reflection can be obtained by placing more than one mirror at certain angle to each other which results in reflection of light for multiple times between reflecting surfaces.

Periscope:

This instrument works on the principle of multiple reflection. A periscope is a tool we use to see things that would otherwise be hidden or obstructed or not in the direct line of sight.

Construction: A reflecting periscope consists of a tube bent twice at right angles. It is provided with two openings and two plane mirror fixed at at the two bends of the tube.. The mirrors are aligned parallel to each other at a $45^{circ}$ angle with the addition of two simple lenses.

Working: The rays of light from the object enter the periscope from one tube (Upper tube in the figure), gets reflected twice and enters the eye of the person looking through the periscope.

Uses of periscope:

It is used in submarine to determine distance objects .

It is used in nuclear reactor to observe different chemical reactions .

In military it is used to observe thing from their hiding positions.

Tanks and armoured vehicles use periscope to inspect the surrounding.

Kaleidoscope :

In this toy beautiful patterns are formed due to multiple reflections. It works on the principle of multiple reflection in inclined plane mirrors. It is a long tube containing mirror and piece of colored glass or paper whose reflection produces changing patterns when tube is rotated.

Kaleidoscope

Construction: Three plane mirrors inclined at an angle of $60^0$ to each other are fixed inside a cylindrical box. A few pieces of coloured glasses are placed inside the box. One end of the cylindrical box has a transparent opening through which a person can view.

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Sample Questions

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Question : 1

Which of the following are correct : (a) In a Kaleidoscope, three plane mirrors inclined at an angle of 90⁰ to each other are fixed inside a cylindrical box. (b) In Periscope, the mirrors are aligned parallel to each other at a 60⁰ angle with the addition of two simple lenses. (c) A periscope is a tool we use to see things that would otherwise be hidden or obstructed or not in the direct line of sight.
A. Only (a) is correct.		B. Only (a) and (b) are correct.
C. Only (c) is correct.		D. None of these
Right Option : C
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Question : 2

A periscope is used in which of the following :
A. Submarine	B. Nuclear reactor	C. Tanks	D. All of these
Right Option : D
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Question : 3

This process of reflection of light several times between reflecting surfaces is known as ________________________ .
A. Multiple reflection of light D	B. Regular reflection of light	C. Diffused reflection of light	D. None of these .
Right Option : A
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