Applicable for both the convex and concave lenses, the lens formula is given as: 1/v - 1/u = 1/f Where, v = Distance of image formed from the optical center 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. Combination of Thin Lenses. Note that the formula is true for a concave lens also. Lens maker's Formula: It is a relation that connects the focal length of a lens to radii of curvature of the two surfaces of the lens and the refractive index of the material of the lens. Using lens formula the equation for magnification can also be obtained as . Q1. Place a thin lens (which is made of one convex surface and one concave surface) between two refractive indices. A 4cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20cm. In that case R 1 is negative, R 2 positive and therefore, f is negative. following assumption are considered while deriving lens maker's formula for concave lens a) only point object is taken b) the aperature of the lens is small Derivation of lens Makers Formula from AB INITIO CONCAVE LENS - Physics - Ray Optics And Optical Instruments This is lens maker’s formula. In other words, the edges of the lens are thicker than the middle. Consider an object O placed on the principal axis of the thin lens. Also find its magnification. Here µ is refractive index of lens material to the medium outside. Equation (5) is known as Lens Maker’s Formula. Let n a be the refractive index of one medium and and n b be the refractive index of second medium. As per optical physics, lens formula relates the distance of an object (u), the distance of an image (v), and the focal length (f) of the lens. In the case of a concave lens, it is always positive. Concave Lens: A concave lens is any lens that has an inward curve in the middle. Lens maker’s formula - Equation 1. m = h 2 /h 1 = v//u = (f-v)/f = f/(f+u) This equation is valid for both convex and concave lenses and for real and virtual images. So, focal length of a lens increases when it is immersed in water. Lens maker s formula and lens formula . This causes light that enters the lens to spread out, or diverge. It is useful to design lenses of desired focal length using surfaces of suitable radii of curvature. 3. If the distance of the object is 30cm from the lens, find the position, nature and size of the image. 2. Of a convex lens of focal length 20cm formula is true for concave! That case R 1 is negative, R 2 lens maker formula for concave lens and therefore, is! Second medium, focal length using surfaces of suitable radii of curvature two refractive indices the edges of image. 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