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:

hi

Explanation:

By definition, the rays stay parallel and go on to infinity when light from an object originates exactly at the focal point. The rays technically shouldn't focus, but practically moving the lens just a millimeter or so can get an image focused on a far away screen the way a projector does. So depending how precise your placement is, you could get a clear, fuzzy, or no image on a screen say 20 feet away. As the screen gets farther away, your image gets larger and dimmer, so it couldn't form a real image at a very far distance anyway let alone infinity. It has just become an expression to say an image is "formed" even though an image is never formed since you can never reach infinity. It would similar to saying that parallel lines "meet" at infinity, but that would contradict the meaning of "parallel". A better description would be to say that an image if formed very far away as an object approaches the focal point.

Answer 2

The answer is -20cm

GIVEN

Magnification = -1

Focal length of convex lens = 10 cm

TO FIND

Object distance from the lens

SOLUTION

We can simply solve the above problem as follows;

We know that,

Magnification is the ratio of image distance to object distance from the lens.

m = v/u

Or,

1/m = u/v (Equation 1)

Where,

m = magnification

v = image distance

u = object distance.

By mirror formula-

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

Multiplying the whole equation by u

$\frac{u}{f} = \frac{u}{v} - 1$

From equation 1

$\frac{u}{f} = \frac{1}{m} - 1$

Or,

$\frac{1}{m} = \frac{u}{f} + 1$

We know that for convex lense u is negative.

m = -1 (Given)

Putting the value of m in equation 1

-1 = u/10 + 1

u/10 = -2

u = -20cm

Hence, The answer is -20cm

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