Where, as the light travels from left to right: R is positive for a convex surface. The lens formula is applicable to both types of lenses - convex and concave. Draw the ray diagram and find the position, size and nature of the image formed. Thick lens (−) (−) n 1 = refractive index outside of the lens. However, if the equation provides a negative focal length, then the lens is a diverging, not converging. Figure 1. n 2 = refractive index of the lens itself (inside the lens). The refraction at a spherical surface. These lenses have negligible thickness. other sign conventions are sometimes used in the literature. Equation (10) is the familiar thin lens formula. It can also be used to calculate image distance for both real and virtual images. Refraction by a thick lens The general problem of refraction by a thick lens is solved by applying the equation for the refraction at one surface to each surface in turn. Convex lenses and the lens equation. Test Your Understanding and Answer These Questions: Define lens formula. Only valid if the focal length is much greater than the thickness of the lens. If the equation provides a negative image distance, then the image formed is virtual and on the same side as the object. Lens 2 Lab Report Magnetic Fields Lab Report Electromagnetic fields 2 Lab Report Preview text Experiment 7: Lens March 24, 2016 Callais 2 I. Lens formula is applicable for convex as well as concave lenses. R is negative for a concave surface. The Lens Equation An image formed by a convex lens is described by the lens equation 1 u + 1 v = 1 f where uis the distance of the object from the lens; vis the distance of the image from the lens and fis the focal length, i.e., the distance of the focus from the lens. Convex lenses and the lens equation; Examples using lens equation; Concave lenses ; Feedback. An object 5 cm high is held 25 cm away from a converging lens of focal length 20 cm. V is the vertex. The ray transfer equation thus becomes: ) = (), ... f = focal length of lens where f > 0 for convex/positive (converging) lens. F u f v object image N.B. The lens formula is applicable both in convex lenses and concave lenses. R 1 = Radius of curvature of First surface. Consider a convex lens with an optical center O. Though we derived it for a real image formed by a convex lens, the formula is valid for both convex as well as concave lenses and for both real and virtual images. Is lens formula applicable only for convex lens? In an exam, the lens equation may be used in a whole host of questions. Let F be the principle focus and f be the focal length. We can use the lens equation that we have previously seen to find the principal focal point. The formula is as follows: $$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$$ Lens Formula Derivation. PURPOSE The purpose of the experiment is to validate the lens equation by measuring the image distance from a fixed focal length and the object distance from the thin lenses for both a single and double lens combination.