Question

1 Write mirror formula & hence find the
image
distanue when an object at a
distance of 15 cm from a concave mirror
of focal length 20 cm.​

Answer 1

Answer:

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Answer 2

Answer:

Here we have been given the object distance and focal length, so first of all we will find out the image distance which will give us the position of image.

(i) Position of image

Here, Object distance, u= -15 cm ( To the left of mirror )

Image distance, v = ? (To be calculated )

And, Focal length, f = -10 cm (It is concave mirror )

Now, putting these values in the mirror formula :

1v+1u=1f

we get : 1v+1−15=1−10

or 1v−115=−110

or 1v=−1101/15

1v=−3+230

1v=−130

So, Image distance, v=−30cm

Thus, the position of image is 30 cm to the left side of mirror or 30 cm in front of mirror (Minus sign shows the left side of morror ).

(ii) Nature of image. Since the image in fornt of the concave mirror, its nature will be "Real and Inverted".

(iii) Size of image. To find the size of image, we will have to calculate the magnification first. The magnification produced by a mirror is given by :

m=−vu

Here, Image distance, v = -30 cm

Object distance, u = -15 cm

So, m=−(−30)(−15)

m=−3015

Magnification, m=-2

We also have another formula for magnification, which is :

m=H2H1

Here, Magnification, m= -2 (Found above )

Height of image, H2=? (To be calculate )

Height of object, H1=1cm (Given)

Now, putting these values in the above magnigication formula, we get :

−2=h21

So, Height of image, H2=−2×1

=-2 cm

Thus, the size of image is 2 cm long. The minus sign here shows that the image is formed below the principle axis. That is, it is a real and inverted image.