- #1
Alex_Neof
- 41
- 2
Homework Statement
A biconvex lens, [itex]L_1[/itex], with focal length of magnitude [itex] \left|
f_1
\right|
= 15[/itex] cm is used with a second biconvex lens, [itex]L_2[/itex], with focal length of magnitude [itex] \left|
f_2
\right|
= 25[/itex] cm to form a compound lens system.
If the two lenses are placed in mutual contact what is the focal length of the compound lens?
Homework Equations
[itex]\frac{1}{f_c} = \frac{1}{f_1} + \frac{1}{f_2}[/itex]
The Attempt at a Solution
It's just a matter of plugging into the above equation.. However do I use the the absolute values or the fact that for a biconvex lens
[itex]
f_1 > 0[/itex]
and
[itex]
f_2 < 0[/itex]?
Solution given is [itex] +9.375 [/itex] cm, which suggests you use the absolute values, however I am not fully convinced as it was not specified in the course notes whether to use absolute values or not.
Not using absolute values, I find the focal length to be [itex] +37.5 [/itex] cm