About the Lens Formula Calculator
What is the Lens Formula Calculator?
The lens formula relates the object distance, image distance and focal length of a thin lens. This calculator uses the New Cartesian sign convention taught in NCERT and CBSE physics.
It tells you where the image forms, how large it is, whether it is real or virtual and the lens power in dioptres.
How to use the Lens Formula Calculator
- Lens (sample: Convex (converging))
- Focal Length (cm, magnitude) (sample: 10)
- Object Distance from the Lens (cm) (sample: 15)
- Object Height (cm) (sample: 2)
- Press Find the Image (results also refresh as you type). The result card shows the Image Distance (v), along with Magnification (m = v ÷ u), Image height, Nature of image and Image forms.
Formula used
1/v − 1/u = 1/f; m = v ÷ u
- Sign convention = u is negative (object on the left); f is + for convex and − for concave
- Power = P = 100 ÷ f (cm), in dioptres
A positive v means a real image on the far side; a negative v means a virtual image on the same side.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Lens | Convex (converging) |
| Focal Length (cm, magnitude) | 10 |
| Object Distance from the Lens (cm) | 15 |
| Object Height (cm) | 2 |
| Result | Value |
|---|---|
| Image Distance (v) | 30 cm |
| Magnification (m = v ÷ u) | -2 |
| Image height | -4 cm |
| Nature of image | Real, inverted, magnified |
| Image forms | On the opposite side of the lens |
| Lens power | 10 D |
Tips for using the Lens Formula Calculator
- An object inside the focal length of a convex lens gives a magnified virtual image – how a magnifying glass works.
- Concave lenses always form virtual, erect, diminished images.