Questions in Ray Optics and Optical Instruments

Select	Question
	An achromatic combination of lenses is formed by joining
	A plano convex lens $(f=20cm)$is silvered at plane surface. Now $f$ will be
	If the central portion of a convex lens is wrapped in black paper as shown in the figure
	A diminished image of an object is to be obtained on a screen 1.0 m from it. This can be achieved by appropriately placing
	The focal length of convex lens is 30 cm and the size of image is quarter of the object, then the object distance is
	A convex lens forms a real image of a point object placed on its principal axis. If the upper half of the lens is painted black, the image will
	In the figure, an air lens of radii of curvature 10 cm (${{R}_{1}}$ = ${{R}_{2}}$ = 10 cm) is cut in a cylinder of glass$(\mu =1.5)$. The focal length and the nature of the lens is
	A lens (focal length 50 cm) forms the image of a distant object which subtends an angle of 1 milliradian at the lens. What is the size of the image
	A convex lens of focal length 12 cm is made of glass of $\mu =\frac{3}{2}$. What will be its focal length when immersed in liquid of $\mu =\frac{5}{4}$
	Two thin lenses of focal lengths ${{f}_{1}}$ and ${{f}_{2}}$ are in contact and coaxial. The combination is equivalent to a single lens of power