A convex lens of focal length 40cm is held at a distance 12cm coaxially above a concave mirror of focale length 18cm. Q. If the convex lens is replaced by a glass plate of thickness 6cm, refractive index `mu=(3)/(2)` and gives rise to an image coincident with itself, then the value of d is equal to A. 20cmB. 30cmC. 40cmD. 60cm

A convex lens of focal length 40cm is held at a distance 12cm coaxiall

1.	A convex lens of focal length 40cm is held at a distance 12cm coaxially above a concave mirror of focale length 18cm. Q. If the convex lens is replaced by a glass plate of thickness 6cm, refractive index `mu=(3)/(2)` and gives rise to an image coincident with itself, then the value of d is equal to A. 20cmB. 30cmC. 40cmD. 60cm
Answer» Correct Answer - a. Shift produced by the glass plate `Deltax=(1-(1)/(mu))t=(1-(2)/(3))6=2cm` For the mirror, the object is placed at a distance `[12+6+d-Deltax]=(16+d)` The image is coincident with the object itself if `(16+d)=36cmrArrd=20cm`

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