#
Hey! listen I'am unable to understand when to place + or - sign in the lens formulae

1
by bappilahri

Log in to add a comment

by bappilahri

Log in to add a comment

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.

The formula is always

1/v - 1/u = 1/f

magnification is m = v/u = h'/h

Sign convention:

1. Distances u , v , f measured against the direction of rays from object are negative. If object on the left, lens on the right side, then u is negative. Focal length for convex lens is +ve. Focal length for concave lens is negative.

2. Distances or heights h or h' of objects and images which are erect (+Y direction) are positive. Inverted lengths h' or h in -y direction are negative.

Substitute +ve or negative sign along with numerical values.

One good thing, you can do, call U, V, F, H, H' to be always positive and equal to |u|, | v | ,....

Then for a concave lens, u = - U, v = - V, f = -F. h = H, h' = H'

For a convex lens for real image, h = H, h' = -H' f = F, u = -U, v = -V.

Make a table of all signs for all virtual and real images for all lenses. Then you will understand it.

1/v - 1/u = 1/f

magnification is m = v/u = h'/h

Sign convention:

1. Distances u , v , f measured against the direction of rays from object are negative. If object on the left, lens on the right side, then u is negative. Focal length for convex lens is +ve. Focal length for concave lens is negative.

2. Distances or heights h or h' of objects and images which are erect (+Y direction) are positive. Inverted lengths h' or h in -y direction are negative.

Substitute +ve or negative sign along with numerical values.

One good thing, you can do, call U, V, F, H, H' to be always positive and equal to |u|, | v | ,....

Then for a concave lens, u = - U, v = - V, f = -F. h = H, h' = H'

For a convex lens for real image, h = H, h' = -H' f = F, u = -U, v = -V.

Make a table of all signs for all virtual and real images for all lenses. Then you will understand it.