JEE MAIN - Physics (2020 - 8th January Evening Slot - No. 2)
An object is gradually moving away from the
focal point of a concave mirror along the axis
of the mirror. The graphical representation of
the magnitude of linear magnification (m)
versus distance of the object from the mirror
(x) is correctly given by :
(Graphs are drawn schematically and are not to scale)
(Graphs are drawn schematically and are not to scale)
_8th_January_Evening_Slot_en_2_1.png)
_8th_January_Evening_Slot_en_2_2.png)
_8th_January_Evening_Slot_en_2_3.png)
_8th_January_Evening_Slot_en_2_4.png)
Explanation
$${1 \over v} + {1 \over u} = {1 \over f}$$
$$ \Rightarrow $$ $${1 \over v} = {1 \over f} - {1 \over u}$$ = $${{u - f} \over {uf}}$$
$$ \Rightarrow $$ v = $${{uf} \over {u - f}}$$
m = -$${v \over u}$$ = $${f \over {f - u}}$$
as u approaches f, m approaches infinity
And at u = 2f, m = –1 or |m| = 1
$$ \Rightarrow $$ $${1 \over v} = {1 \over f} - {1 \over u}$$ = $${{u - f} \over {uf}}$$
$$ \Rightarrow $$ v = $${{uf} \over {u - f}}$$
m = -$${v \over u}$$ = $${f \over {f - u}}$$
as u approaches f, m approaches infinity
And at u = 2f, m = –1 or |m| = 1
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