Q26
1 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.

mirrorscreenfocal lengthdistant object

Marking Scheme

  • 1Correct 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.

Analysis & 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).

Common Mistakes

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

Interesting Facts

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

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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.