The Focal Length of a Lens?

In summary, an object located 26.0cm from a certain lens forms a real image that is twice as high as the object. The first lens has a focal length of 5.77cm, but the sign convention needs to be taken into account. In part 2, a new diverging lens with the same focal points as the first lens is used and an object 5.00cm high is located 26.0cm from the lens. The height of the image formed by the new lens can be found using the formula m = -i/o and taking into account the sign convention.
  • #1
thurrucane
1
0

Homework Statement



An object is located 26.0cm from a certain lens. The lens forms a real image that is twice as high as the object.

(i) What is the focal length of this lens?

(ii) Now replace the lens used in Part 1 with another lens. The new lens is a diverging lens whose focal points are at the same distance from the lens as the focal points of the first lens. If the object is 5.00cm high, what is the height of the image formed by the new lens? The object is still located 26.0cm from the lens.

Homework Equations



Since the image is real and 2X as large, the magnification m = -2. The formula
m = -i/o
1/o + 1/i = 1/f

The Attempt at a Solution



After attempting part 1 i got 5.77cm which is incorrect.
 
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  • #2
You got to take care of the sign convention.
 

1. What is the definition of focal length?

The focal length of a lens is the distance between the lens and the point where light rays converge to form a sharp image on the film or sensor.

2. How is focal length measured?

Focal length is typically measured in millimeters (mm) and can be found on the lens itself. It is the distance from the center of the lens to the point of convergence of light rays.

3. What is the difference between a longer and shorter focal length?

A shorter focal length means a wider field of view, allowing you to capture more of the scene in your photo. A longer focal length results in a narrower field of view, making distant objects appear closer and larger in your photo.

4. How does focal length affect image quality?

Focal length does not have a direct effect on image quality. However, different focal lengths may have different optical properties that can affect the sharpness, distortion, and depth of field in your photos.

5. Can the focal length of a lens be changed?

Yes, the focal length of a lens can be changed by using a zoom lens or by physically changing the lens to one with a different focal length. Some lenses also have the ability to change their focal length through adjustable elements within the lens itself.

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