question about lenses

[donaldduck]

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Is it possible for i to be positive while o is negative or vica versa? I am not understanding this at all! someone told me that this wont likely be on the test how accurate of a statement is this? Also, any other pointers or helpful rules on lenses that u may want to throw in will be helpful thanks!

 

[Rabolisk]

i can certainly be negative if o is positive. If you have a negative f (diverging lens, mirrors) that happens. If o < f, then it also occurs. The latter is when you put an object closer than the focal length of a converging lens or concave mirror. When i is negative and o is positive, you get a virtual, upright image.