An object is placed at the focus of concave lens having focal length f. What is the magnification and distance of the image from the optical centre of the lens?

Question

An object is placed at the focus of concave lens having focal length f. What is the magnification and distance of the image from the optical centre of the lens? (A) 1, ∞ (B) Very high, ∞ (C) (1/2), (f/2) (D) (1/4), (f/4)

Tardigrade Admin · Accepted Answer

<img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/c04a916e9a5e4dcc01d2a1d40cc0b719-.png" /> U =- f (1/ V )-(1/ U )=(1/- f ) ⇒ (1/ V )=-(2/ f ) V =(- f /2) m =( V / U )=(1/2) distance =( f /2)

Q. An object is placed at the focus of concave lens having focal length $f$ . What is the magnification and distance of the image from the optical centre of the lens?

$1, \infty$

Very high, $\infty$

$\frac{1}{2}, \frac{f}{2}$

$\frac{1}{4}, \frac{f}{4}$

$U = - f$
$\frac{1}{V} - \frac{1}{U} = \frac{1}{- f}$
$\Rightarrow \frac{1}{V} = - \frac{2}{f}$
$V = \frac{- f}{2}$
$m = \frac{V}{U} = \frac{1}{2}$
distance $= \frac{f}{2}$

Q. An object is placed at the focus of concave lens having focal length f. What is the magnification and distance of the image from the optical centre of the lens?

1,∞

Very high, ∞

21​,2f​

41​,4f​