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# how do v decide the sign of image dis nd object dis in case of lens whenever we get d sign of the image +ve how do v decide dat its on RHS or LHS OF D LENS.In case of mirror when object is some dis in front of it then image will b formed same dis at d back of it.is it same for object behind d mirror.how do v decide real and virtual object nd image in case of mirror

SAGAR SINGH - IIT DELHI
879 Points
10 years ago

Dear student,

Lens Formula

Lens formula: The expression which shows the relation between u, v and f is called lens formula.

1/f = 1/v – 1/u

1/f = (µ – 1) {1/R1 – 1/R2}

Magnification

The ratio of the size of the image to the size of object is called magnification.

(i)         Transverse magnification : m = 1/O = v/u = f/f+u = f–v/f (use sign convention while solving the problem)

(ii)        Longitudinal magnification : m = 1/O = v2–v1/u2–u1. For very small object

m = dv/du = (v/u)2 = (f/f+u)2 = (f–v/f)2

(iii)       Areal magnification : ms = Ai/Ao = m2 = (f/f+u)2

(Ai = Area of image, Ao = Area of object)

Gurwinder Kaur
65 Points
10 years ago

draw diagram.it will clear from that wht is sign of v. it will also clear frm dat diagram that the image is real or virtual.