Derivation of Lensmaker’s formula. Lens Maker’s formula is a formula that relates focal length, radii of curvature, and refractive index of the lens. Here µ is refractive index of lens material to the medium outside. The lens maker formula is utilized to create a lens with a defined focal length. Starting with an expression for refraction at a single spherical surface, obtain Lens Maker's Formula. MEDIUM. [Since it is a biconvex lens, f is positive, R 1 is positive and R 2 is negative. The radii of curvature here are measured according to the Cartesian sign convention.For a double convex lens the radius R 1 is positive since it is measured from the front surface and extends right to the center of curvature. You may substitute the same values for the focal length in air and the radii of curvature of the faces in the l ens maker’s equation and satisfy yourself that the refractive index of the lens is 1.5. A number of idealizations, simplifications and approximations are used to Before understanding the formula, let us look at some terminology you need to know. ... Derivation. A lens has two curved surfaces, but both are not exactly same. the lensmaker’s formula relates the index of refraction, the radii of curvature of the two surfaces of the lens, and the focal length of the lens. Consider two thin convex lenses L 1 and L 2 of focal length f 1 and F 2 placed coaxially in contact with each other. (a) 0.667 (b) 1.5 (c) 0.5 (d) zero (e) data insufficient. View Answer. The magnification of an object placed in front of a convex lens … So, focal length of a lens increases when it is immersed in water. Lensmaker’s Formula by C. Bond Lenses with the same shape and index of refraction will have the same focal length. Also, put the numerical values of R 1 and R 2 equal to f]. We assume a thin, converging lens and that the light rays we are dealing with are close to the principal axis and make very small angles with the principal axis ( angles of less than 10 o), resulting in very small angles of incidence. The formula giving the relation between the focal length (f) of the lens, the refractive index of the material of the lens (n) and the radii of curvature of its surface (R 1 & R 2) is known as Lens maker formula.. For a thin lens, the power is approximately the sum of the surface powers.. By using the lens maker’s formula you can determine the focal length of the specific lens if you know the parameters such as refractive index and radius of curvature. Prerequisites As different devices need lenses of different focal lengths, this formula helps lens manufacturers in finding the radii of curvature. Click hereto get an answer to your question ️ Derive lens maker's formula for a biconvex lens. The radius R 2 is negative since it extends left from the second surface. Lens-Maker's Formula. The manufacturers of the lenses use this relation to design the lens of a … This is lens maker’s formula. Combination of Thin Lenses.