Question

what is magnification produce by concave mirror of focal length 20cm when object is assistance of 15 cm from it​

Answer 1

Answer:

Given:-

• Mirror is concave
• Focal length is 20cm..... let focal length be 'f'
• Object is at 15cm.....let object distance be 'u'
• let image distance be 'v'
• let magnification be 'm'

So it means the object is between pole and focus..... so the image is going to be formed in the mirror means the value of 'v' must be positive....

"Note:- In a concave mirror all the values are in '-' except for the image distance formed when the image is virtual and erect."

u = -15cm

f = -20cm

v = ?

1/v + 1/u = 1/f

1/v +(-1/15) = -1/20

1/v - 1/15 = -1/20

15 - v/15v = -1/20

20(15 - v) = -15v

300 - 20v = -15v

300 = 5v

v = 60

As expected the value of 'v' is positive....

The image is thus formed in the mirror as it is the only case of concave mirror in which the image is virtual and erect.....

So m = -v/u = -60/-20 = 3

So image formed is 3 times larger than the object height....

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