A convex lens of focal length f produces a real image of size is 1 n times the size of the object. Find the position of the object.

According to the question, it is given that, Focal length of convex length = f And, magnification of lens, m = 1 n Image distance u , we have to calculate. Sine image is real ∴ m = v u = - 1 n Or, u = - n v .....................(i) Now from lens formula 1 f = 1 v - 1 u = 1 v - 1 - n v = 1 v + 1 n v ∴ n v = f n + 1 Substituting the value of n v , in (i) n u = - f n + 1 ∴ u = f n + 1

The dispersive powers of the material of the two lenses are in the ratio of 4 3 . If the focal length of this achromatic combination is 60 cm , find the focal length of the lenses.

For an achromatic combination of lenses, f 1 f 2 = - ω 1 ω 2 . . . i here: ω 1 ω 2 = 4 3 . . . ii From the equation i and ii So, f 1 f 2 = - 4 3 or f 1 f 2 = - 4 3 f 2 . Now the combined focal length of the lens is given by 1 F = 1 f 1 + 1 f 2 1 60 = - 3 4 f 2 + 1 f 2 ∵ F = 60 cm 1 60 = - 3 + 4 4 f 2 4 f 2 = 60 ∴ f 2 = 15 cm and f 1 = - 4 3 f 2 f 1 = - 4 3 × 15 f 1 = - 20 cm . Hence, the focal length of component lenses is + 15 cm and - 20 cm .

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Beta Question Bank for Medical: Physics>Chapter 30 - Ray Optics>BEGINNER'S BOX - 6>Q 5

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IMPORTANT

Earn 100

An object placed 20 cm in front of a convex lens has its image 40 cm behind the lens. Find the power of the lens.

Important Questions on Ray Optics

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Beta Question Bank for Medical: Physics>Chapter 30 - Ray Optics>BEGINNER'S BOX - 6>Q 6

A lens shown in figure is made of two different materials. A point object is placed on its axis. How many images will be formed.

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Beta Question Bank for Medical: Physics>Chapter 30 - Ray Optics>BEGINNER'S BOX - 6>Q 7

A convex lens of focal length f produces a real image of size is

\frac{1}{n}

times the size of the object. Find the position of the object.

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Beta Question Bank for Medical: Physics>Chapter 30 - Ray Optics>BEGINNER'S BOX - 6>Q 8

A ray of light strikes a glass plate at an angle of

60 °

. If the reflected and the refracted rays are perpendicular to each other, find the index of refraction of glass.

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Beta Question Bank for Medical: Physics>Chapter 30 - Ray Optics>BEGINNER'S BOX - 7>Q 1

In the displacement method, the distance between the object and the screen is

70 cm

and the focal length of the lens is

16 cm

, find the separation between the magnified and diminished image position of the lens.

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Beta Question Bank for Medical: Physics>Chapter 30 - Ray Optics>BEGINNER'S BOX - 7>Q 2

An achromatic doublet of focal length 90 cm si to be made of two lens. The material of one of the lenses has 1.5 times the dispersive power of the other. The doublet is converting type. Find the focal length of each lens.

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Beta Question Bank for Medical: Physics>Chapter 30 - Ray Optics>BEGINNER'S BOX - 7>Q 3

The dispersive power of material of a lens of focal length