alleryStart learning →Cartesian sign convention: positive or negative?
Exercise and reference answers
- Items
- Item
- Measured along the incident light
- Category
- Positive
- Item
- Height above the principal axis
- Category
- Positive
- Item
- Focal length of a convex mirror
- Category
- Positive
- Item
- Measured against the incident light
- Category
- Negative
- Item
- Height below the principal axis
- Category
- Negative
- Item
- Focal length of a concave mirror
- Category
- Negative
- Categories
- Item
- Positive
- Item
- Negative
Explanation
Distances measured in the SAME direction as the incident light are positive, those opposite are negative, and all are measured from the pole or optic centre.
Heights above the axis are positive.
Source: syllabus Physics Part II, Ch 9 Ray Optics and Optical Instruments.
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