the principal axis of a convex lens is along x-axis. the coordinates of a point object and it's image are (-20cm,2cm) and (25cm, -4cm ).the focal length of lens will be
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Answers
Given that The principle axis lies along the x axis then :
The image and the object distances are the values of x in the given points.
The object distance is = -20 cm
Image distance = 25 cm
We will use the lens formula to get the focal length.
The lens formula is as follows :
1/f = 1/u + 1/v
Doing the substitution we have :
1/f = 1/25 -1/20 = -1/100
f = -100 cm
The focal length is -100 cm
Focal length: The distance between the center of a lens and its focus is called the focal length.
Given:
X axis coordinate of the object (-20cm, 2cm)
X axis coordinate of the image (25cm, -4cm)
Solution:
According to lens formula,
1 / f = 1 / v - 1 / u
The distance of object distance u = -20 cm
The distance of image distance v = 25 cm
The focal length,
f = ( u v ) / ( u - v )
f = ( - 20 x 25 ) / ( -20 - ( -25 ) )
f ≅ 10 cm
Hence, the focal length is 10 cm.
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