A thin piece if wire 4.00mm long is located in a plpaneperpendicular to the optical axis and 60.0cm in front of a thinlens. The sharp image of the wire formed on a screen is 2.0mm long.What is the focal length of the lens?

asked 2021-04-26
A thin piece if wire 4.00mm long is located in a plpaneperpendicular to the optical axis and 60.0cm in front of a thinlens. The sharp image of the wire formed on a screen is 2.0mm long.What is the focal length of the lens?

Answers (1)

The object distance u = 60cm
height of the real, inverted image \(\displaystyle{h}_{{{i}}}=-{2}{m}{m}\)
height of object \(\displaystyle{h}_{{{0}}}={4}{m}{m}\)
Thus, the magnification \(\displaystyle{M}=\frac{{h}_{{{i}}}}{{h}_{{{0}}}}=-\frac{{v}}{{u}}\)
- 2 / 4 = - v / 60
calculating we get v = 30cm
The focal lenghtof the lens is calculated using
1 / f = 1 / u + 1 / v
= 1 / 60 + 1 / 30
Thus, f = 20cms
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