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
Answers
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.
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How far should an object be from the pole of a concave mirror of focal length 20 cm to form a real image whose size is 1/5th of the object.?
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∆ 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
Thus the focal length of the pin is 30 cm.