The focal length of the lens will be 3.32 cm. The object is placed in front of a convex lens.
The focal length of the lens, which is often expressed in millimeters, is the distance between the lens and the image sensor when the subject is in focus.
Given data;
Focal length,f=?
Image distance,v= -12.8 cm
Object distance,u=
Magnification,m= 2.85
The magnification of the lens is found as;
[tex]\rm m=\frac{v}{u} \\\\ u=\frac{v}{m} \\\\ u=\frac{-12.8}{2.85} \\\\\ u= -4.49 \ cm[/tex]
- ve shows that the image is formed behind the mirror.
The mirror equation is found as;
[tex]\rm \frac{1}{f} =\frac{1}{v} +\frac{1}{u} \\\\ \rm \frac{1}{f} =\frac{1}{-12.8} -\frac{1}{4.9} \\\\ \frac{1}{f} = -0.3008 \\\\\ f= 3.32 \ cm[/tex]
Hence the focal length of the lens will be 3.32 cm.
To learn more about the focal length refer;
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