# A convex lens of power 3 D is held in contact with a concave lens of power -1D.A parallel beam of light is made to fall on the combination. At what di

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A convex lens of power 3 D is held in contact with a concave lens of power -1D.A parallel beam of light is made to fall on the combination. At what distance from the combination will the beam get focussed?

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Here, P_1=3D,P_2= -1D, F=?
P=P_1 +P_2=(3-1)=2D
F=100/P = 100/2= 50cm
:. The beam will get focussed at a distance of 50cm from the combination of lenses.