Negative focal lengthreal or virtual

Finding the focal length of a negative lens is important because it allows us to understand the properties of the lens and how it will affect the image formation. It also helps in determining the appropriate distance between the lens and the object for a clear and sharp image.

Focal lengthof convex mirror is positive ornegative

CAUTION: IT IS EXTREMELY IMPORTANT THAT EVERYONE WEARS SAFETY GOGGLES WITH THIS DEMO. Be sure to have extra people to ensure everyone (including volunteers!) wears safety goggles and does not touch anything that has been melted.

Yes, the focal length of a negative lens can be calculated without another lens. This can be done by using the lens equation, which relates the focal length to the distance between the lens and the object, and the distance between the lens and the image.

Focal length

A Fresnel lens replaces a traditional curved lens by adding concentric grooves to the surface of the lens, as seen below left. These grooves act as individual refracting surfaces that turn a light source into parallel rays that can be seen for very long distances, as in the case of the lighthouse. In our demo we take the light in the opposite direction. We face those grooves toward the sun, and its incoming parallel rays, to concentrate the light down to a single point. Fresnel lenses are mostly used for light gathering power not for precision imaging.

To find the focal length of a negative lens without another lens, you will need to measure the distance between the lens and the object (u) and the distance between the lens and the image (v). Then, plug these values into the lens equation (1/f = 1/u + 1/v) and solve for f. This will give you the focal length of the negative lens.

Overview: A Fresnel lens can be looked at as many layers of lenses cut and stacked on top of each other. Creating a lens in this manner provides great collecting or great dispersion power. Lighthouses use Fresnel lenses to project light miles out into the ocean. In this demo, we turn that same lens around to collect and focus sun light into a spot that is so powerful that it will melt rocks. While Fresnel lenses can collect a lot of light in a compact lightweight package, they do not have very good resolution

The lens equation is a mathematical formula that relates the focal length of a lens to the distance between the lens and the object (u) and the distance between the lens and the image (v). It is written as 1/f = 1/u + 1/v, where f is the focal length of the lens.

Negative focal lengthmirror

Objectives: Learn more about a type of lens structure that can be lightweight, for its size, yet very powerful at the same time for the way it collects light.