Question

A 10 million metre long penis placed vertically in front of a concave mirror a 5 million long images formed at a distance of 30 cm from the mirror what is the focal length of the mirror

Answer 1

The focal length of the pin is 30 cm.

Explanation:

Correct statement:

A 10 mm long awl pin is placed vertically in front of a concave mirror.A 5 mm long awl pin is formed at a distance of 30 cm in front of mirror.Find the focal length of the mirror?​

Solution:

size of object = O = 10.0 mm = 1.0 cm (as, 1 cm = 10 mm)

Size of the image = 0.5 cm                                                      

Image distance(v) = −30 cm  

Let the object distance be u.

Focal length = ??

Magnification (m)= -v/u

I/O = -v/u

0.5/1 = -30/u

= -60 cm

By using lens mirror formula 1/f = 1/v + 1/u

= 1/-30 +1/-60

= -2-1/60

= -3/60

= 20 cm

Focal length(f) = 30 cm

Thus the focal length of the pin is 30 cm.

Also learn more

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Answer 2

∆ Answer :-

size of object = O = 10.0 mm = 1.0 cm (as, 1 cm = 10 mm)

Size of the image = 0.5 cm                                                      

Image distance(v) = −30 cm  

Let the object distance be u.

Focal length = ??

Magnification (m)= -v/u

I/O = -v/u

0.5/1 = -30/u

= -60 cm

By using lens mirror formula 1/f = 1/v + 1/u

= 1/-30 +1/-60

= -2-1/60

= -3/60

= 20 cm

Focal length(f) = 30 cm

$\to$ Thus the focal length of the pin is 30 cm.