1.

find the position of an object which when placed in front of a concave mirror of a focal length 20 cm produces virtual image which thrice the size of object​

Answer» <html><body><h3><u>Answer</u> :-</h3><p></p><p>Position of the object is <strong><u>13.33 <a href="https://interviewquestions.tuteehub.com/tag/cm-919986" style="font-weight:bold;" target="_blank" title="Click to know more about CM">CM</a></u></strong> from the mirror .</p><p></p><h3><u><a href="https://interviewquestions.tuteehub.com/tag/explanation-455162" style="font-weight:bold;" target="_blank" title="Click to know more about EXPLANATION">EXPLANATION</a></u> :-</h3><p></p><p>We have :-</p><p>→ <a href="https://interviewquestions.tuteehub.com/tag/focal-2648683" style="font-weight:bold;" target="_blank" title="Click to know more about FOCAL">FOCAL</a> length = <strong>2</strong><strong>0</strong><strong> </strong><strong>cm</strong></p><p>→ Size of image is thrice the object .</p><p><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong></p><p></p><p>From the question, we have :-</p><p>• hᵢ = 3hₒ</p><p></p><p>Now, from the formula of Magnification of spherical mirror :-</p><p></p><p><strong>m </strong><strong>=</strong><strong> </strong><strong>-</strong><strong>(</strong><strong>v/</strong><strong>u)</strong><strong> </strong><strong>=</strong><strong> </strong><strong>h</strong><strong>ᵢ</strong><strong>/</strong><strong>h</strong><strong>ₒ</strong></p><p>⇒ -(v/u) = 3hₒ/hₒ</p><p>⇒ -(v/u) = 3</p><p>⇒ v/u = -3</p><p>⇒ v = -3u</p><p><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong><strong><u>_</u></strong></p><p></p><p>According to sign convention :-</p><p>• f = -20 cm</p><p></p><p>Now, let's calculate the position of the object by using the mirror formula .</p><p></p><p><strong>1</strong><strong>/</strong><strong>v </strong><strong>+</strong><strong> </strong><strong>1</strong><strong>/</strong><strong>u </strong><strong>=</strong><strong> </strong><strong>1</strong><strong>/</strong><strong>f</strong></p><p>⇒ 1/(-3u) + 1/u = 1/(-20)</p><p>⇒ -1/3u + 1/u = -1/20</p><p>⇒ (-1 + 3)/3u = -1/20</p><p>⇒ 2/3u = -1/20</p><p>⇒ 3u(-1) = 2(20)</p><p>⇒ -3u = <a href="https://interviewquestions.tuteehub.com/tag/40-314386" style="font-weight:bold;" target="_blank" title="Click to know more about 40">40</a></p><p>⇒ u = 40/(-3)</p><p>⇒ <u>u = -13.33 cm</u></p><p></p><p>[According to sign convention, 'u' is always <strong>-ve </strong>for a <a href="https://interviewquestions.tuteehub.com/tag/concave-927978" style="font-weight:bold;" target="_blank" title="Click to know more about CONCAVE">CONCAVE</a> mirror.]</p></body></html>


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