A lens of power +1 D is made in contact with another lens of power -2 D the combination will then act as a:

Step-by-step solution

The power of a combination of thin lenses in contact is given by the algebraic sum of the individual powers of the lenses: P = P₁ + P₂ . Given P₁ = +1 D and P₂ = -2 D , the effective power P is: P = 1 D + (-2 D ) = -1 D . The focal length f of the combination is given by f = 1 P in meters. f = 1 -1 D = -1 m = -100 cm . Since the power is negative, the combination acts as a diverging lens. The magnitude of the focal length is 100 cm . Answer: diverging lens of focal length 100 ~cm