Question 261 markMCQSection B

Dhoni obtained the image of a distant object on a screen by using a concave mirror. To find the focal length of the mirror he should measure the distance between

Light — Reflection and Refraction
Spherical Mirrors

Options

(A)the mirror and the screen as well as between object and the screen
(B)mirror and the screen
(C)object and the screen
(D)object and the mirror

Official answer

To find the focal length of a concave mirror using a distant object, the distance between the mirror (pole) and the screen (where the sharp image is formed) should be measured.

Answer keywords:mirrorscreenfocal lengthdistant object

Marking scheme

  1. 1.Correct option selection (1 mark)

Hint

Rays from a distant object are considered parallel to the principal axis.

Quick oral answer

The image of a distant object is formed at the focus of a concave mirror. Thus, the distance between the mirror and the screen is the focal length.

Common mistakes

  1. 1.Measuring the distance from the object to the mirror instead of the image to the mirror.

Analysis and explanation

According to Activity 9.2 in the NCERT text, light from a distant source (like the Sun or a distant object) is converged by a concave mirror at its principal focus. The image of a distant object is formed at the focus. Therefore, the distance between the pole of the mirror and the screen (position of the image) gives the approximate focal length (ff).

Interesting facts

This method only gives an 'approximate' focal length because the object might not be at true infinity.

Question details

Q26 of 41 questions

Board
CBSE
Class
Class 10
Subject
Science
Year
2011
Section
Section B
Marks
1
Type
MCQ
Chapter
Light — Reflection and Refraction
Topic
Spherical Mirrors
Bloom's level
Understand
Syllabus topic
Reflection of light by spherical mirrors; Focal length

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Frequently asked questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 1 mark in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Light — Reflection and Refraction" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Spherical Mirrors" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a MCQ question from Section B in the CBSE Class 10 Science 2011 paper.