Simulation · Physics · Class 12
Two thin lenses
From the lesson Power of a lens and combinations of thin lenses in Ray Optics and Optical Instruments. Change the values and watch what happens.
Two thin lensesPhysics · Class 12
The idea behind it
NCERT § "Power of a Lens"
- The power of a lens is the reciprocal of its focal length in metres, P = 1/f. Its SI unit is the dioptre (D), 1 D = 1 m⁻¹.
- A converging lens has positive power; a diverging lens has negative power.
- Two thin lenses in contact behave as one lens with 1/f = 1/f₁ + 1/f₂, so powers add: P = P₁ + P₂ + ….
- The total magnification of a combination is the product of the individual magnifications: m = m₁m₂m₃….
- Lenses are combined in instruments to raise magnification and to reduce certain aberrations; a combination also lets designers make lenses of the required power.
- For lenses separated by a distance, find the image formed by the first lens and use it as the object (real or virtual) for the next lens, measuring each distance from that lens.