Answer:
The focal lenth (F) =+10.0cm
Explanation:
The formular for combined focal length (F) is given as;
[tex]1/f = 1/f_{1} + 1/f_{2}[/tex]
In this question,
F1 = 20cm
F2 = -30cm
Plugging the values into the formuar above,
[tex]1/f = 1/20 + 1/(-30)[/tex]
[tex]1/f = 0.05 - 0.033
[tex]1/f = -0.017
f = [tex]1/ -0.017[/tex]
f = 58.82cm
i.e. the combination behaves as a converging lens (because of the postive sign) of focal length 58.82cm .
This question involves the concepts of focal length and the combination of lenses.
The focal length of the given combination is "60 cm".
The focal length of the combination of lenses is given by the following formula:
[tex]\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}[/tex]
where,
Therefore,
[tex]\frac{1}{f} = \frac{1}{20\ cm}-\frac{1}{30\ cm}\\\\[/tex]
f = 60 cm
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