Where is sign convention in the question
Answers
Answer:
Explanation:
today in our physics test, we were given the following question:-
A mirror has focal length 20 cm and produces an image 1/3 the size of an object. Find the object distance
The question is pretty straightforward but the problem me and my classmates faced was whether to take the focal length as +ve or -ve or both.
What I used to think was that if a distance was given without a sign we will assume it to be positive. And hence, in my solution I took the given mirror to be convex (Cartesian Convention)
But my friend said that if focal length is given without a sign it refers to the magnitude of focal length.Thus, they solved the problem for both concave and convex mirrors.
In the nutshell, my question is Is 20cm the same as +20 cm or not?
I feel that my question is not much of a conceptual question but one regarding the convention of assigning signs to distances.Also I couldn't refer to my textbook as in all problems the mirror was specified as convex or concave beforehand.