^Sign conventions

Following are the sign conventions for all types of mirrors, lenses, spherical refracting surfaces

1. All distances are measured from the pole of the mirror.

2. Distances measured in the direction of incident ray are +ve & that measured in the opposite direction are –

3. Distances measured upward to the principle axis are +ve & that measured downward are –

Using the image formation rules, sign conventions & simple laws of geometry we can prove the relation between u, v, f, m, I, O, f, R & P.

Don’t put the sign for the quantity to be calculated.

^Convergent power

1. Bends the reflected (or refracted) rays towards the principal axis

2. Has positive optical power

3. e.g. a concave mirror & a convex lens (placed in rarer surroundings)

4. our eyes

5. Used in compound microscope, telescopes, cameras.

^Virtual focus

1. A position on the principal axis where two or more reflected (or refracted) rays appears to meet
2. situated infront of mirror
3. g. focus of a convex mirror & that of a concave lens (placed in rarer surroundings)

^Virtual image

1. A position where two or more reflected (or refracted) rays appears to meet
2. situated behind the mirror & behind the object on same side of lens
3. v = + ve for mirrors & – ve for lenses.
4. Can’t be obtained on screen, without using a convergent system.

^Virtual object

1. A position at which incident rays converge

2. situated behind the mirror i.e. towards the polished side

3. u = + ve for both lenses & mirror