In order to obtain a real image of magnification 2 using a converging lens of focal length 20 cm , where should an object be placed?

Question

In order to obtain a real image of magnification 2 using a converging lens of focal length 20 cm , where should an object be placed? (A) 50 cm (B) 30 cm (C) -50 cm (D) -30 cm

Tardigrade Admin · Accepted Answer

For real image m=-v e m=-2 ∴ As we know M =( f / u + f ) -2=(f/u+f) ⇒ -2=(20/u+20) ⇒ -2 u+(-40)=20 u =-30 cm

Q. In order to obtain a real image of magnification 2 using a converging lens of focal length $20 c m,$ where should an object be placed?

$50 c m$

$30 c m$

$- 50 c m$

$- 30 c m$

For real image $m = - v e$
$m = - 2$
$∴$ As we know $M = \frac{f}{u + f}$
$- 2 = \frac{f}{u + f}$
$\Rightarrow - 2 = \frac{20}{u + 20}$
$\Rightarrow - 2 u + (- 40) = 20$
$u = - 30 c m$

Q. In order to obtain a real image of magnification 2 using a converging lens of focal length 20cm, where should an object be placed?

50cm

30cm

−50cm

−30cm