**What happens when two lenses are placed together?**

**05/15/17**

*“How do we solve a physics problem with two lenses placed together?”*

When doing a geometric optics problems, we often assume the lenses to be discrete from one another. However, what happens when we have** two lenses right next to each other?** Well, let’s think about it using our mathematical mindset. If we look carefully, then we will notice that the same amount of light will be incoming and outgoing for both sides. This is similar to how the voltage drop on two parallel resistors is the same. So what if we were to treat our optical system in a similar manner? Well, after much research into this matter, opticists have shown that both lenses can be replaced with an **equivalent lens **with a focal length given by the equation 1/f_combined=1/f1+1/f2.

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