With reference to the Periscope, consider the following statements: 1. It works on the principle of multiple reflections. 2. It uses two plane mirrors arranged at right angles to each other. 3. It allows viewing of objects that are not directly in the line of sight. Which of the statements given above are correct?

Correct Option The correct option is (c) 1 and 3 only. Explanation A periscope is an optical instrument used to observe objects from a concealed position or when the direct line of sight is obstructed. It operates based on the laws of reflection using plane mirrors or prisms. Statement-wise Analysis - Statement 1 is Correct: The working of a periscope relies on the principle of multiple reflections. Light from an object strikes the first mirror, is reflected through the tube, strikes the second mirror, and is reflected again to reach the observer's eye. - Statement 2 is Incorrect: In a simple periscope, the two plane mirrors are arranged parallel to each other, not at right angles. Each mirror is fixed at an angle of 45° to the axis of the tube. This specific arrangement ensures that light turns 90° at the first mirror and another 90° at the second mirror, allowing the final emergent ray to be parallel to the incident ray. If the mirrors were at right angles to each other, the light would be reflected back toward the source (retro-reflection). - Statement 3 is Correct: The primary function of a periscope is to enable the viewing of objects situated above, below, or around an obstacle (such as a wall, trench, or water surface) that prevents direct line-of-sight observation. It is widely used in submarines and military bunkers. Key Takeaway: A simple periscope utilizes two plane mirrors placed parallel to each other and inclined at 45° to the optical path to view obstructed objects through successive reflections.

With reference to the Periscope, consider… - NCERT Class 8 Science MCQ

NCERT Class 8 Science — Chapter 4: Light

mcqmedium

With reference to the Periscope, consider the following statements:

It works on the principle of multiple reflections.
It uses two plane mirrors arranged at right angles to each other.
It allows viewing of objects that are not directly in the line of sight.

Which of the statements given above are correct?

NCERT textbook question

From NCERT Science - class 8 · Page 169

Options

A1 and 2 only
B2 only
C1 and 3 only
D1, 2 and 3

Did you get this right?

Solution

Correct Option

The correct option is (c) 1 and 3 only.

Explanation

A periscope is an optical instrument used to observe objects from a concealed position or when the direct line of sight is obstructed. It operates based on the laws of reflection using plane mirrors or prisms.

Statement-wise Analysis

Statement 1 is Correct: The working of a periscope relies on the principle of multiple reflections. Light from an object strikes the first mirror, is reflected through the tube, strikes the second mirror, and is reflected again to reach the observer's eye.
Statement 2 is Incorrect: In a simple periscope, the two plane mirrors are arranged parallel to each other, not at right angles. Each mirror is fixed at an angle of 45° to the axis of the tube. This specific arrangement ensures that light turns 90° at the first mirror and another 90° at the second mirror, allowing the final emergent ray to be parallel to the incident ray. If the mirrors were at right angles to each other, the light would be reflected back toward the source (retro-reflection).
Statement 3 is Correct: The primary function of a periscope is to enable the viewing of objects situated above, below, or around an obstacle (such as a wall, trench, or water surface) that prevents direct line-of-sight observation. It is widely used in submarines and military bunkers.

Key Takeaway: A simple periscope utilizes two plane mirrors placed parallel to each other and inclined at 45° to the optical path to view obstructed objects through successive reflections.

Your note

More from Chapter 4: Light

With reference to image formation by a plane mirror, consider the following statements: 1. The image formed cannot be obtained on a screen. 2. The image appears at a greater distance behind the mirror than the object is in front. 3. The image undergoes lateral inversion. Which of the statements given above are correct?

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Consider the following statements about the image formed by a plane mirror: 1. It is inverted vertically. 2. It is of the same size as the object. 3. It appears to be at the same distance behind the mirror as the object is in front. Which of the statements given above is/are correct?

easy

In the context of the reflection of light, what does the term 'angle of incidence' refer to?

easy

With reference to the eye's ability to see, consider the following statements: 1. A normal eye can clearly see distant objects as well as objects nearby. 2. The minimum distance for distinct vision is constant at 50 cm for all ages. 3. In old age, eyesight may become foggy due to the eye lens becoming cloudy. Which of the statements given above is/are correct?

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With reference to the eyes of animals, consider the following statements: 1. Crabs have large eyes that allow them to look only in the front. 2. Butterflies have large eyes composed of thousands of little eyes. 3. Owls have a small cornea and pupil to restrict light entry. Which of the statements given above are correct?

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