Questions in Ray Optics and Optical Instruments

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	The unit of focal power of a lens is
	A thin lens made of glass of refractive index $\mu = 1.5$ has a focal length equal to 12 cm in air. It is now immersed in water $\left( \mu \,=\,\frac{4}{3} \right)$. Its new focal length is
	Figure given below shows a beam of light converging at point P. When a convex lens of focal length 16 cm is introduced in the path of the beam at a place O shown by dotted line such that OP becomes the axis of the lens, the beam converges at a distance x from the lens. The value x will be equal to
	If two $+ 5 D$ lenses are mounted at some distance apart, the equivalent power will always be negative if the distance is
	A convex lens produces a real image m times the size of the object. What will be the distance of the object from the lens
	A convex lens is made up of three different materials as shown in the figure. For a point object placed on its axis, the number of images formed are
	An object is placed 12 cm to the left of a converging lens of focal length 8 cm. Another converging lens of 6 cm focal length is placed at a distance of 30 cm to the right of the first lens. The second lens will produce
	If convex lens of focal length $80cm$ and a concave lens of focal length $50 cm$ are combined together, what will be their resulting power
	A point object O is placed in front of a glass rod having spherical end of radius of curvature 30 cm. The image would be formed at
	The focal length of lens of refractive index 1.5 in air is 30 cm. When it is immersed in a liquid of refractive index $\frac{4}{3}$, then its focal length in liquid will be

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