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An Object of Size 7.0 Cm is Placed at 27 Cm in Front of a Concave Mirror of Focal Length 18 Cm. at What Distance from the Mirror Should a Screen Be Placed So that a Sharp Focussed Image Can Be Obtained? Find the Size and Nature of Image. - Science

An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed so that a sharp focussed image can be obtained? Find the size and nature of image. 

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Distance of the object from the mirror 'u' = −27 cm
Height of the object 'ho' = 7 cm
Focal length of the mirror 'f' = −18 cm
We have to find the distance of the image 'v' and height of the image 'hi'.
Using the mirror formula, we get   


⇒ `1/-18=1/v-1/27` 

⇒ `1/-18=1/v-1/27` 

⇒ `1/27-1/18=1/v` 

⇒ `(-1)/54=1/v` 

⇒ v=-54 cm 

Thus, the distance of the image 'v' is 54 cm.
Now, using the magnification formula, we get 



`h_i=-14 cm` 

Therefore, the height of the image 'hi' is 14 cm.
Again, using the magnification formula, we get 



Thus, the image is real, inverted and large in size.

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Lakhmir Singh Class 10 Physics (Science)
Chapter 4 Reflection of Light
Q 17 | Page 198
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