Question

Please answer this question...

Answer 1

HEY MATE YOUR ANSWER IS HERE

OBJECT DISTANCE (U) = -2m

GIVEN THAT :-

MAGNIFICATION ( M ) = 1/4

NOW ,

$m \: = \frac{1}{4} \\ \\ m = \frac{v}{u} \\ \\ \frac{1}{4} = \frac{v}{u} \\ \\ \frac{1}{4} = \frac{v}{ - 2} \: \: (given \: u = - 2) \\ \\ v \: = - \frac{1}{2} = - 0.5 \: m \\ \\ \\ now \: \\ \\ by \: lens \: formula \: \\ \\ \frac{1}{f} \: = \frac{1}{v} - \frac{1}{u} \\ \\ \frac{1}{f} = \frac{1}{( - 0.5)} - \frac{1}{( - 2)} \\ \\ \frac{1}{f} = - \frac{3}{2} \\ \\ f = - \frac{2}{3} \\ \\ hence \: lens \: is \: concave \:$

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Answer 2

Explanation:

Given,

=> object distance (u) = -2m

=> object distance (u) = -2m=> Image Form 1/4 th of object.

A.T.Q

• By Using Lens Formula [ 1/v - 1/u = 1/f ]

$\bold {\large = > \frac{1}{v} - \frac{1}{u} = \frac{1}{f}}$

=> Magnification (M) = 1/4 = v/u

$\red{\boxed {\huge m= {\frac{1}{4} = \frac{v}{u}}}}$

$\bold {\large = > \frac{1}{4} = \frac{v}{ - 2}}$

$\bold {\large = > v = - 0.5m\:or\: - \frac {1} {2} }$

$\bold {\large \frac{1}{f} = \frac{1}{ - 2} - \frac{1}{ - \frac {1}{2}}{lens\:formula \:here}}$

$\bold {\large \frac{1}{f} = \frac{ - 1 + 4}{ - 2} = \frac{3}{ - 2}}$

$\bold {\large - \frac {2}{3} =f}$

focal of Lens = $\large{-\frac{2}{3}}$

☆ ★ Hence the lens is concave.

Thank You ☺️ ☺️....

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