Lens & Mirror Calculator
Calculate image distance, focal length, magnification, and power for convex/concave lenses and mirrors using the lens formula (1/f = 1/v − 1/u) and mirror formula (1/f = 1/v + 1/u). Follows the New Cartesian Sign Convention used in CBSE.
Lens & Mirror Calculator
Lens sign convention: distances measured from optical centre. Object side (left) = negative.
Image Distance (v)
30 cm
Using lens formula: 1/f = 1/v − 1/u
Magnification (m)
-1×
Image Height
-5 cm
Power of Lens
6.6667 D
Image Nature
Real, inverted, same size
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Sign Convention: Object distance (u) is always negative. Focal length: concave mirror/convex lens = negative/positive. Image distance (v): positive if on the same side as the observer.
Power: P = 1/f (in metres) = 100/f (in cm). Measured in dioptres (D).
Frequently Asked Questions
What is the mirror formula?
The mirror formula is 1/f = 1/v + 1/u, where f is the focal length, v is the image distance, and u is the object distance. For concave mirrors, f is negative (by the new Cartesian sign convention used in CBSE). For convex mirrors, f is positive.
What is the lens formula?
The lens formula is 1/f = 1/v − 1/u. For a convex (converging) lens, f is positive. For a concave (diverging) lens, f is negative. Object distance u is always negative (object is on the same side as incoming light).
What is magnification and how is it calculated?
Magnification (m) = height of image / height of object = −v/u for mirrors and v/u for lenses. If m is positive, the image is erect (virtual). If m is negative, the image is inverted (real). |m| > 1 means the image is magnified; |m| < 1 means it is diminished.
What is the power of a lens?
Power (P) = 1/f, where f is in metres. Power is measured in dioptres (D). A convex lens has positive power, and a concave lens has negative power. This concept is used in CBSE Class 10 (Light chapter) and Class 12 (Ray Optics). Power of combination = P₁ + P₂.