Triangle on a concave mirror

JEE Advanced 2018 Paper 2, Question 4

A wire is bent in the shape of a right angled triangle and is placed in front of a concave mirror of focal length f, as shown in the figure. Which of the figures shown in the four options qualitatively represent(s) the shape of the image of the bent wire? (These figures are not to scale.)

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Related article: Optics without ray diagrams: Mirrors


If the object is kept between a concave mirror and its focal point the image is virtual and upright (see this note). Recall that an object at a distance …

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Optics without ray diagrams: Mirrors

The usual discussions of geometrical optics often rely too heavily on ray diagrams to locate the image and study its properties. We will demonstrate that all of these insights can be obtained purely by algebra on the mirror equation. Developing these instincts will help us solve optics problems without having to use crude, hand drawn, and often inaccurate ray diagrams. Our main results are summarized in the table below.

We begin by recalling the mirror equation

(1)   \begin{equation*}   \frac{1}{p} + \frac{1}{q} = \frac{1}{f} , \end{equation*}

where p and q the distances of the object and image from the mirror, and the focal length f=R/2, for a spherical mirror with …

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