The magnification of an object placed in front of a convex lens of focal length 20cm is +2. To obtain a magnification of -2, the object has to be moved by a distance equals to

10cm

No worries! We‘ve got your back. Try BYJU‘S free classes today!

30cm

No worries! We‘ve got your back. Try BYJU‘S free classes today!

20cm

Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses

40cm

No worries! We‘ve got your back. Try BYJU‘S free classes today!

Open in App

Solution

The correct option is C 20cm
$m = \frac{v}{u} = 2 u = - x, v = - 2 x, f = + 20 Using lens formula, \frac{1}{v} - \frac{1}{u} = \frac{1}{f} \Rightarrow \frac{1}{- 2 x} + \frac{1}{x} = \frac{1}{20} \Rightarrow x = 10 c m To have magnification, -2 u = - y, v = 2 y a n d f = 20 c m \Rightarrow \frac{1}{2 y} + \frac{1}{y} = \frac{1}{20} \Rightarrow y = 30 c m ∴ y - x = 30 - 10 = 20 c m$

Suggest Corrections

Similar questions

Q. The magnification of an object placed in front of a convex lens is +2. The focal length of the lens is 2 metres. Find the distance by which object has to be moved to obtain a magnification of -2 (in metres). ___

Q. The magnification of an object placed in front of a convex lens of focal length

20 cm

+ 2

. To obtain a magnification of

- 2

, the object has to be moved by a distance equal to:

When an object is placed in front of a concave mirror of focal length f, a virtual image is produced with a magnification of 2. To obtain a real image with a magnification of 2, the object has to be moved by a distance equal to

Q. An object is placed in front of a concave mirror focal length

f

. An erect image is formed with a magnification of

2

. To obtain real image with the same magnification, the object has to be moved through a distance of:

Join BYJU'S Learning Program

The magnification of an object placed in front of a convex lens of focal length 20cm is +2. To obtain a magnification of -2, the object has to be moved by a distance equals to

The correct option is C 20cmm=vu=2u=−x,v=−2x,f=+20Using lens formula,1v−1u=1f⇒1−2x+1x=120⇒x=10 cmTo have magnification, -2u=−y,v=2y and f=20 cm⇒12y+1y=120⇒y=30 cm∴y−x=30−10=20 cm