# Two lenses: find Di through second lens

• tensor0910
In summary, the problem involves an object placed 20.0 cm to the left of a lens with a focal length of 10.0 cm. A second lens with a focal length of 36.0 cm is placed 44.0 cm to the right of the first lens. The goal is to calculate the distance of the image formed. Using the equation 1/f = 1/di + 1/do and the fact that the image is twice the size of the object, it is determined that the image is real, inverted, and located 82.28 cm to the right of the second lens. However, this answer is incorrect and upon further analysis, it is determined that the first image is a real image to
tensor0910
Gold Member

## Homework Statement

A 1.60 cm tall object is 20.0 cm to the left of a lens with a focal length of 10.0 cm . A second lens with a focal length of 36.0 cm is 44.0 cm to the right of the first lens.

## Homework Equations

1/f = 1/di + 1/do , hi/ho = di/do

## The Attempt at a Solution

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calculate distance of image

1/f = 1/di + 1/do
1/10cm - 1/20cm = 1/di

20cm = di

with a image twice the length of the object, it must be a converging lens. its inverted and real.
image of first lens becomes object of second lens.

do = 20 +44 = 64cm

f = 36cm

1/36 - 1/64 = 1/di

82.28cm = di

But MP says its wrong...?

The only thing I can think of is that the signs are wrong somewhere, but the image is real so it should be positive... Any and all help is appreciated!

tensor0910 said:
image of first lens becomes object of second lens.

do = 20 +44 = 64cm

!

Your first image is a real image to the right of the first lens so how far is it from the second lens?

tensor0910
Cutter Ketch said:
Your first image is a real image to the right of the first lens so how far is it from the second lens?

yup that makes sense. Thanks for the help Cutter!

tensor0910 said:
yup that makes sense. Thanks for the help Cutter!
You're welcome

## 1. How do I find the focal length of the second lens?

The focal length of a lens can be found by using the lens maker's equation: 1/f = (n-1)(1/R1 + 1/R2), where f is the focal length, n is the refractive index of the lens material, and R1 and R2 are the radii of curvature of the lens surfaces. You can also measure the focal length by using a lens bench or by performing an experiment with known distances.

## 2. What is the relationship between the focal length of the first and second lens?

The focal length of the second lens affects the overall magnification and image formation. The relationship between the focal lengths of the two lenses is given by the thin lens equation: 1/f1 + 1/f2 = 1/d, where f1 and f2 are the focal lengths of the two lenses and d is the distance between them. This equation shows that a shorter focal length for the second lens will result in a larger overall magnification.

## 3. Can I use any type of lens for the second lens?

The type of lens used for the second lens will depend on the specific setup and experiment. However, in general, the second lens should have a focal length that is larger than the first lens in order to produce a real image. Convex lenses are commonly used for the second lens as they have a positive focal length and can produce real images.

## 4. How does the distance between the two lenses affect the image produced?

The distance between the two lenses, known as the lens separation, plays a crucial role in determining the overall magnification and image formation. As the lens separation increases, the overall magnification decreases, and the image formed becomes smaller. However, there is a limit to how far apart the two lenses can be before the image becomes distorted and loses clarity.

## 5. What factors can affect the accuracy of finding Di through the second lens?

Factors that can affect the accuracy of finding the image distance (Di) through the second lens include the accuracy of measuring the focal lengths of the lenses, the alignment of the lenses, and the precision of the experimental setup. It is important to minimize any sources of error and to perform multiple trials in order to obtain a more accurate result.

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