Question

Where would you have to place an object in order to get same size image( give answer in bullet

point only.)

​

Answer 1

In order to get the same size of the image as that of object, place the object on the radius of curvature.

Explanation

Assume that an object AB is placed at centre of curvature. Now, draw a parallel ray to principal axis such that it will pass through the focus. Similarly, draw an another ray that pass through focus such that it will reflect back parallel to the principal axis.

If we join both the rays we will found that the image formation of the object takes place but in downward direction. The image formed will be real, inverted and same size as that of the object.

$\rule{200}2$

LET'S TAKE AN EXAMPLE TO UNDERSTAND IT:

A convex lens has focal length 20cm. Atwhat distance from the lens should the object be placed so that the image is formed 40cm on the other side of the mirror. Find nature of the image formed.

Solution:

Using Lens formula:

1/f = 1/v - 1/u

Substitute the known values,

→ 1/20 = 1/40 - 1/u

→ 1/u = 1/40 - 1/20

→ 1/u = -1/40

→ u = -40

(Image formed is real.)

Therefore, the object distance from the lens is 40 cm.

Now, using magnification formula:

m = v/u

Substitute the values,

→ m = 40/(-40)

→ m = -1

As, the image distance and object distance from the lens is same; means the object is placed at C due to this image is also formed at C. Also, the height of image and object are same.

Answer 2

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• ✒(1️⃣) Where the object should be placed to obtain an image of the same size in convex lens...?✔

• ✒(2️⃣) Where the object should be placed to obtain an image of the same size in Concave lens...?✔

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$\sf\large{\underline{\underline{\red{\implies\:Answer.}}}}$(1️⃣)

✏To obtain an image of the same size in Convex lens, the object is placed at 2F1 (twice the first focal length) in a convex lens, then the image formed is;

• $\sf\large{\green{Real}}$
• $\sf\large{\red{Inverted\: and}}$
• $\sf\large{\orange{Of\: the\: same\: size}}$

✏Object should be placed at 2F or Centre Of Curvature C1 of Convex Lens, to get image of given property.✍

$\sf\large{\underline{\underline{\red{\implies\:Answer.}}}}$(2️⃣)

• ✏To obtain an image of the same size in $\sf\large{\underline{\green{Concave\: Mirror,}}}$the object should be placed at he centre if curvature of the concave mirror to obtain an image of same size and real image.✍

• ✏When the object is placed on the centre of curvature, on the principle axis, in front of a concave lens, the image is formed at the same point. The image formed is real and inverted.✍