Moving an object and screen to find the focal length of a lens

In summary, a convex lens with a magnification of m1 is used to project the image of an object on a screen. When the object is moved along the optical axis by a distance Δs and the screen is moved to locate the image again, the new magnification is m2. The focal length can be calculated using the equation Δs/(1/m2-1/m1).
  • #1
nofootcanman
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Homework Statement


A convex lens is used to project the image of an object on a screen with a magnification m1 . Leaving the lens fixed, the object is moved along the optical axis
by a distance Δs and the screen is moved until the image is located again. If the new
value of the magnification is m2 , Show that the focal lenghth [itex]\frac{Δs}{\frac{1}{m_{2}}-\frac{1}{m_{2}}}[/itex]


Homework Equations


s'/s=m
1/s+1/s'=1/f
Where s is the position of the object and s' is that of the image/screen

The Attempt at a Solution


I used s1=s2+Δs and attempted to rearrange but got nowhere really.. any suggestions?
 
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  • #2
nofootcanman said:
I used s1=s2+Δs and attempted to rearrange but got nowhere really.. any suggestions?
Please show your work then, so we can see what went wrong.
 

1. What is the purpose of moving an object and screen to find the focal length of a lens?

The purpose of moving an object and screen is to determine the focal length of a lens. This is an important measurement in optics, as it tells us how much the lens can bend light and how far away the image will be focused.

2. How do you set up the experiment to find the focal length of a lens?

To set up the experiment, place the lens on a flat surface and place the object (such as a candle or a ruler) at a distance from the lens. Then, move the screen (such as a piece of paper) behind the lens until a clear and focused image of the object is formed.

3. What is the relationship between the distance of the object and the screen in finding the focal length of a lens?

The relationship between the distance of the object and the screen is known as the thin lens equation: 1/f = 1/o + 1/i, where f is the focal length, o is the distance of the object from the lens, and i is the distance of the image from the lens. By varying the distance of the object and the screen, we can solve for the focal length of the lens.

4. How many trials should be conducted to find the most accurate focal length of a lens?

It is recommended to conduct at least three trials to find the most accurate focal length of a lens. This will allow for any errors or inconsistencies to be identified and for an average to be taken, resulting in a more precise measurement.

5. Can this experiment be done with any type of lens?

Yes, this experiment can be done with any type of lens as long as it is a convex lens (thicker in the middle and thinner at the edges). Concave lenses are not suitable for this experiment as they disperse light instead of focusing it.

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