Questions in Ray Optics and Optical Instruments

Select	Question
	The focal length of a combination of lenses formed with lenses having powers of + 2.50 D and – 3.75 D will be
	Focal length of a converging lens in air is R. If it is dipped in water of refractive index 1.33, then its focal length will be around (Refractive index of lens material is 1.5)
	Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens when immersed in a liquid of refractive index of 1.25 will be
	The focal length of a convex lens depends upon
	If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power
	${{f}_{v}}$and ${{f}_{r}}$ are the focal lengths of a convex lens for violet and red light respectively and ${{F}_{v}}$ and ${{F}_{r}}$are the focal lengths of a concave lens for violet and red light respectively, then
	If a lens is cut into two pieces perpendicular to the principal axis and only one part is used, the intensity of the image
	A convex lens of focal length $f$ produces an image $\frac{1}{n}$ times than that of the size of the object. The distance of the object from the lens is
	Two thin lenses whose powers are +2D and –4D respectively combine, then the power of combination is
	A substance is behaving as convex lens in air and concave in water, then its refractive index is