Question

explain the sign convention rule for mirror and lens

Answer 1

$\underline{\underline{\Huge\mathfrak{Answer}}}$

In case of spherical mirrors, the following sign convention is used for measuring various distances:

a). All distances are measured from the pole of the mirror.

b). All distances measured in the direction of the incident ray are taken as positive.

c). All distances measured in the direction opposite to that of the incident ray are taken as negative.

d). The distances measured above the principal axis are taken as positive.

e). The distances measured below the principal axis are taken as negative.

Answer 2

General lens formula :

1 / f = 1 / v - 1 / u

Signs to remember :

For convex lens :

f = positive always .

v = negative for virtual and positive for real .

u = negative always .

For concave lens :

f = negative always .

v = negative always .

u = negative always .

Sign conventions :

⇒ The optical centre is the origin .

⇒ All distances right of the centre is taken positive.

⇒ The distances left of the centre is negative.

⇒ The distances above the centre is positive.

⇒ The distances below the centre is negative.

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