How to find the focal length of a lens (Problem with a task)

Thread starter Sajo
Start date Feb 11, 2021
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Focal Focal length Length Lens

In summary, the focal length of a lens can be found using the lens equation or through a simple experiment. It is typically measured in millimeters or centimeters, but can also be measured in meters or inches. Any lens can be used to find the focal length as long as it has a measurable focal length and can form an image. The focal length of a convex lens is positive, while the focal length of a concave lens is negative. The curvature of a lens directly affects its focal length, with a greater curvature resulting in a shorter focal length and a flatter curvature resulting in a longer focal length. This is due to the curvature's role in bending light as it passes through the lens.

Feb 11, 2021

Sajo

Homework Statement: Determine the optical power of a biconvex lens, with a radius of curvature of both spherical surfaces of 20 cm each, which is made of glass with a refractive index of 1.83 in water. The refractive index for water is 1.33

Relevant Equations: Optical power=1/focal length of lens

Hello. I need formulas for the focal length of a lens when I have refractive indices of two centers and two radii of curvature of spherical surfaces or one radius of curvature of spherical surfaces. I search the internet but can't find it.

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Feb 11, 2021

berkeman

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Welcome to PhysicsForums.

Keywords are "Lensmaker Equation":

https://en.wikipedia.org/wiki/Lens#Lensmaker's_equation

1. What is the focal length of a lens?

The focal length of a lens is the distance between the lens and the point where the light rays converge to form a sharp image. It is typically measured in millimeters (mm) and is one of the key characteristics of a lens.

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

To find the focal length of a lens, you can use the thin lens equation: 1/f = 1/o + 1/i, where f is the focal length, o is the object distance, and i is the image distance. You can also measure the distance between the lens and the point where the image is formed using a ruler or measuring tape.

3. What is the difference between a positive and negative focal length?

A positive focal length means that the lens is a converging lens, which means it brings parallel light rays together to form an image. A negative focal length indicates a diverging lens, which spreads out parallel light rays and forms a virtual image.

4. Can I use any object to find the focal length of a lens?

Yes, you can use any object as long as it is placed at a distance from the lens that is significantly greater than the focal length. This will ensure that the image formed is sharp and the thin lens equation can be used accurately.

5. How does the focal length affect the image produced by a lens?

The focal length of a lens determines the magnification and field of view of the image produced. A shorter focal length will result in a wider field of view and smaller magnification, while a longer focal length will produce a narrower field of view and larger magnification.