Magnification carries a positive or negative sign in mirror and lens problems.
a. (i) State the expression for linear magnification in terms of object distance u and image distance v for (a) spherical mirrors and (b) thin lenses.
b. (ii) Explain why a positive magnification corresponds to an erect image while a negative magnification corresponds to an inverted image, referring to the Cartesian sign convention for heights.
c. (iii) Illustrate your explanation with one worked numerical example each for a mirror and for a lens, choosing appropriate values of u and f so that one gives positive magnification and the other negative magnification.