Calculating Focal Length of a Converging Lens Using Object and Image Distances

In summary, the focal length of the converging lens can be found using the equation 1/f = 1/do + 1/di, where f is the focal length, do is the object distance, and di is the image distance. In this case, a 3.0 cm tall object placed 20 cm in front of the lens forms a real image 10 cm from the lens, resulting in a focal length of 6.667 cm. For a visual representation, refer to the provided links on ray diagrams.
  • #1
whitehorsey
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Lens -- find the focal length

1. An object 3.0 cm tall is placed 20 cm in front of a converging lens. A real image is formed 10 cm from the lens. What is the focal length of the lens?



2. 1/f = 1/do + 1/di



3. 1/f = 1/do + 1/di
1/f = 1/20 + 1/10
f = 6.667 cm

I'm not sure if this is right and if you can can you show me how the diagram would look like. Thank You!
 
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  • #4


Thank You!
 

1. What is the focal length of a lens?

The focal length of a lens is the distance between the lens and its focal point when the lens is focused on an object at infinity. It is usually measured in millimeters (mm) and determines the magnification and field of view of the lens.

2. How do you find the focal length of a lens?

The focal length of a lens can be found by using the lens formula, which is 1/f = 1/u + 1/v, where f is the focal length, u is the distance between the object and the lens, and v is the distance between the lens and the image. You can also find the focal length by measuring the distance between the lens and its focal point.

3. What is the relationship between focal length and magnification?

The focal length of a lens is directly proportional to its magnification. This means that the longer the focal length, the higher the magnification and the narrower the field of view. On the other hand, a shorter focal length will result in a lower magnification and a wider field of view.

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

Yes, the focal length of a lens can be changed by adjusting the distance between the lens and the sensor or film in a camera. This is usually done by moving the lens closer or further away from the camera body using the focusing ring. Some lenses also have a zoom function that allows you to change the focal length to achieve different magnifications.

5. How does the focal length affect depth of field?

The focal length of a lens is one factor that affects depth of field, which is the range of distance that appears in focus in an image. A longer focal length will result in a shallower depth of field, while a shorter focal length will result in a deeper depth of field. This means that a longer focal length is ideal for portraits or close-up shots, while a shorter focal length is better for landscapes or group photos.

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