Two coaxial convex lenses are placed at a distance of 45 cm from each other. A beam of light parallel to the principal axis is incident on the first lens and emerges from the second lens also parallel to the principal axis. If the optical power of the first lens is +4 D , the optical power of the second lens is :

Step-by-step solution

The focal length of the first lens is given by f₁ = 100 P₁ = 100 4 = 25 cm . For a beam of light parallel to the principal axis to emerge parallel after passing through both lenses, the second principal focus of the first lens must coincide with the first principal focus of the second lens. This forms an afocal system. The distance between the two lenses is d = f₁ + f₂ . Substituting the given values: 45 = 25 + f₂ f₂ = 20 cm The optical power of the second lens is P₂ = 100 f₂ = 100 20 = +5 D . Answer: +5 D