I don't know how to take focal length, image distance and object distance positive or negative in lenses and mirrors?

### Asked by lokendersikarwar6 | 10th Jun, 2019, 12:33: PM

Expert Answer:

### The distance measured in the direction of incident light is taken as positive whereas distances measured in the direct opposite to the direction of incident light is taken as negative.This is applicable for both mirror and lenses.E.g when we measure object distance we always start measuring distance from optical centre/pole towards the object and while doing this we are moving in the direction which is opposite to the direction of incident light, and therefore object distance is taken as negative.

### Answered by Utkarsh Lokhande | 10th Jun, 2019, 12:57: PM

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