Question

if jagruthi obtained a magnification of -1 with convex lens of focal length 10cm what is the object distance from the lens​

Answer 1

Answer:

The focal length of a convex lens is 10 cm. What will be the object distance if the linear magnification is 1?

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1 Answer



Vinod Gohel

, former Retired professor of physics at Gujarat University (1962-2003)

Answered 2 years ago · Author has 2.9K answers and 6.3M answer views

Lateral- Magnification, m of a lens ( both convex and concave ) is defined by ratio of height of image , hi to height of object, ho.

Therefore,

m= hi/ho.

The formula of magnification can also be obtained in terms of image and object distances v and u respectively.

Then,

m= hi/ho= v/u……….(1)

Now, for a thin spherical lens,

(1/v)-(1/u)= (1/f)

We multiply this equation by u. This gives

(u/v)-(1)=u/f. But (u/v)=(1/m). Therefore ,

(1/m)-1=u/f OR

(1/m)=(u/f)+1 …..(1)

Now, for convex lens m is negative when ho is erect and hi is inverted.

Therefore , in our problem, m=-1.

Putting this value in equation (1), we get

-1= (u/10)+1 OR

u/10 = -2 OR

u= -20 cm.