## Question

You are given two identical plano-convex lenses. When you place an object 20 cm to the left of a single plano-convex lens, the image appears 40 cm to the right of the lens. You then arrange the two plano-convex lenses back to back to form a double convex lens. If the object is 20 cm to the left of this new lens, what is the approximate location of the image?

### Solution

10 cm to the right of the lens

Focal length for the combination,

*v* = 10 cm (to the right)

#### SIMILAR QUESTIONS

An achromatic convergent lens combination is made by keeping in contact a convex lens of focal length 20 cm and a concave lens of focal length 30 cm. Dispersive power of the material of convex lens is 0.18. Find the dispersive power of the material of the concave lens, and the focal length of the combination.

The dispersive powers of crown and flint glasses are 0.02 and 0.04 respectively. Find the focal length of the convex lens of crown glass which forms achromatic doublet with a concave lens of flint glass of focal length 80 cm.

For an achromatic combination of lenses, the ratio of dispersive powers of materials used in lenses is 2:3. One lens has focal length equal to 10 cm. Find focal length, power and nature of second lens.

An achromatic objective lens of a telescope is made of two lenses of crown and flint glasses. If the dispersive powers of crown and flint glasses are 0.02 and 0.03, and the focal length of the lens made from crown glass is 16.0 cm, find the focal length of the lens made of flint glass. Also find the focal length of the combination.

The focal length of an achromatic combination of two lenses is 60 cm. If the ratio of the dispersive powers of the two lenses is 5/3, then find out the focal length of the two lenses.

An achromatic combination of objective lens of a telescope is made of crown and flint glasses. Focal length of the combination is 0.25 meter. If the dispersive powers of crown and flint glasses are 0.02 and 0.03 respectively, then find the power of each lens of the combination.

A beam of light passes from medium 1 to medium 2 to medium 3 as shown in fig. What may be concluded about the three indices of refraction,*n*_{1}, *n*_{2} and *n*_{3}?

A ray of light in incident on a medium with angle of incidence *i* and refracted into a second medium with angle of refraction *r*. the graph of sin(*i*) vs sin (*r*) is shown in fig. Then, the velocity of light in the first medium in *n* times the velocity of light in the second medium. What should be the value of *n*?

A beam of light propagates through a medium 1 and falls onto another medium 2, at an angle α_{1} as shown in fig. After that, in propagates in medium 2 at to an angle α_{2} as shown. The light’s wavelength in medium 1 is λ_{1}. What is the wavelength of light in medium 2?

Light from a denser medium 1 passes to a rarer medium 2. When the angle of incidence is θ the partially reflected and refracted rays are mutually perpendicular. The critical angle will be