How to measure the focal length of a convex lens? What else is a convex lens called?

A convex lens is a common lens that is thick in the middle and thin at the edges. At least one surface is made into a spherical surface, or both surfaces can be made into spherical surfaces. It plays a magnifying role. How to measure the focal length of a convex lens? I guess many friends have not studied this aspect, let's take a look!

Contents of this article

1. How to measure the focal length of a convex lens

2. What else is a convex lens called?

3. Which convex lens is more focused, a large or small diameter lens?

How to measure the focal length of a convex lens

The focal length measurement methods of convex lenses include the formula method, conjugate method, parallel light focusing method, and distant object imaging method.

Use an optical bench to conduct an experiment on how a convex lens forms a real image. Measure and record the object distance u and image distance v during imaging. Calculate the focal length f of the lens based on the lens imaging formula and take the average value after multiple measurements.

Use the optical bench to fix the positions of the light source and the screen, and measure the distance L between them. Place the convex lens of the focal length to be measured between them, and move the convex lens along the main axis so that the inverted image of the light source appears twice on the screen. Record the position of the lens during the two imagings, and then calculate the distance d that the lens moves during the two imaging processes. According to the formula, the focal length f of the convex lens can be calculated. This method is called the conjugate method. This is one of the commonly used methods for measuring the focal length of convex lenses in laboratories.

According to the characteristics of convex lens, let parallel light (such as sunlight) incident on the convex lens along the main axis direction, place a light screen parallel to the lens on the other side, and adjust the position of the light screen to make the light spot on the light screen smallest and brightest. At this time, the distance between the lens and the light screen is the focal length of the convex lens. This is a simple method to roughly measure the focal length of the convex lens.

In the laboratory, the distant object imaging method can be used instead of the parallel light focusing method to estimate the focal length of a convex lens. The method is similar to the parallel light method. Adjust the position of the light screen so that distant objects (such as the window of a classroom or objects outside the window) are imaged on the light screen. The distance between the light screen and the lens is approximately the focal length of the lens.

What is a convex lens called?

Convex lens is also called converging lens, because it can converge light. Convex lens is made according to the principle of light refraction. Convex lens is thicker in the center and thinner at the edge. Convex lens can be divided into double convex, plano-convex and concave-convex. Thicker convex lens can have telescopic and converging effects, which is related to the thickness of the lens. Hyperopia glasses are convex lenses. Convex lens has magnifying effect. Convex lens has double focal length, small and large, and single focal length, real, virtual, positive and inverted.

Which convex lens is more focused, a large one or a small one?

The diameter of a convex lens has nothing to do with its focusing ability, but from the convex lenses seen in physics laboratories, those with larger diameters have longer focal lengths, that is, poor focusing ability; those with smaller diameters have shorter focal lengths, that is, strong focusing ability.

Convex lens is a common lens, which is thick in the middle and thin at the edges. At least one surface is made into a spherical surface, or both surfaces can be made into spherical surfaces. It plays a magnifying role. The multiples vary. Convex lens has a magnifying effect. Convex lens has two focal lengths, large and small, and one focal length, real and virtual, positive and inverted. In fact, neither convex lens nor concave lens has a certain focus. Only light rays that are parallel to the main optical axis and at the same distance from the main optical axis will completely intersect on the main optical axis. The reason why we see that many light rays that are parallel to the main optical axis but at unequal distances from the main optical axis passing through the convex lens have a focus is because the radius of curvature of the convex lens is large, and the difference in the degree of light deflection is not obvious. For ease of use, we take the intersection of two light rays that are equal in distance from the main optical axis and the top of the convex lens as the focus of the convex lens.