Assertion:A convex lens and a concave lens are kept in contact. If the thickness of a lens is negligible in comparison to the radius of curvature, it is a thin lens.

Reason: Power of a concave lens is always less than the power of a convex lens, as power of concave lens is negative whereas power of convex lens is positive. Combination of Thin Lenses. The lens has a focal length of 15.2 cm. The lens maker's formula can be derived for a concave lens in the same way. Queries asked on Sunday & after 7pm from Monday to Saturday will be answered after 12pm the next working day. Here µ is refractive index of lens material to the medium outside. But from the ray diagram we see that OC = AB, From equation (1) and equation (2), we get. Similarly a concave lens can be made convergent. The two formulas given above are together referred to as the thin lens formula. Numericals based on concave/convex lens and power ... Q1. For a concave lens, R1 is negative and R2 is positive. (a) Lens Maker’s Formula: Suppose L is a thin lens. Define lens formula. Calculate the position of the images formed by the fol-lowing concave lenses. A student performs an experiment to find the radius (R) of an equi-convex thin lens and refractive index μ (> 1) of a liquid. A 4 cm tall candle is placed in front of a double convex lens. The magnification (\(M\)) of the image formed can be calculated using the following formula. P24.85), the lens maker’s formula has a slightly different form: This relation always gives a negative focal length f as expected for a double concave lens (because it … This video introduces lenses and gives the lens makers formula. (viii) represents Lens maker formula. Verify your number to create your account, Sign up with different email address/mobile number, NEWSLETTER : Get latest updates in your inbox, Need assistance? The refractive index of the material of lens is n 2 and it is placed in a medium of refractive index n 1.The optical centre of lens is C and X ' X is principal axis. The following typical equation is used to determine a relation between the focal length of the lens, the distance of the object, and the distance of the image. Solve application questions using a thin lens formula by joining other students here at BYJU’S. The refractive index of lens is 1.5. Derivation of Lens Maker Formula for a Concave Lens. For a Concave (diverging) Lens; R1 = negative. This video explains the types of curved mirrors and few of their uses. Let O be a point object lying in the rarer medium on the principal axis of the refracting surface X 1 P 1 Y 1. Contact us on below numbers. Required fields are marked *, Thin Lens Formula For Concave And Convex Lenses. Be careful with the sign of the focal length in the lens formula! A concave lens of focal length 15 cm forms an image 10 cm from the lens. If ‘\(i\)’ is positive, the image is upright and if ‘\(i\)’ is negative, the image is inverted. The radii of curvature of the surfaces of the lens are R 1 and R 2 and their poles are P 1 and P 2.The thickness of lens is t, which is very small. Lens maker’s formula for a double concave lens. Kindly Sign up for a personalized experience. = (μ − 1) × (R1. (a)For an object with u= 12cmif the focal length is 4cm From this, we can come to the conclusion that a convex lens doesn’t necessarily have to be converging and concave diverging. The Lensmaker's formula works with this convention, although you can modify the formula and define your reference system accordingly. Derivation of Lens Formula for concave lens: Let AB represent an object placed at right angles to the principal axis at a distance greater than the focal length f of the convex lens. For a double convex lens the radius R1 is positive since it is measured from the front surface and extends right to the center of curvature. Please post different questions as separate queries. OF 1 = Focal length … The object has been placed 45.7 cm from the vertex. derive lens formula for convex lens when virtual image is formed. An object 5 cm high is held 25 cm away from a converging lens of focal length 20 cm. First, what is a thin lens? If the distance of the object is 30cm from the lens, find the position, nature and size of the image. R2 = positive. 1 / (-20.0) = 1 / (12.0) + 1 / d i. For a double concave lens (Fig. 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. All rights reserved. If the image distance is calculated to be negative, it implies that the image formed is virtual and on the same side as the object. So, focal length of a lens increases when it is immersed in water. Exercise 2. They will behave as a diverging lens if focal length of convex lens is more. f = negative. The image A1B1 is formed between O and F1 on the same side as the object is kept and the image is erect and virtual. Ans: Image distance = 22.8 cm; Image Height = -1.99 cm. Want a call from us give your mobile number below, For any content/service related issues please contact on this number. If the focal length is negative, it implies that the lens is concave (diverging), while if positive it implies that the lens is convex (converging lenses). If the focal length is negative, it implies that the lens is concave (diverging), while if positive it implies that the lens is convex (converging lenses). Let a concave lens have two spherical surfaces X 1 P 1 Y 1 and X 2 P 2 Y 2 having radius of curvature as R 1 and R 2 respectively. The image A 1 B 1 is formed between O and F 1 on the same side as the object is kept and the image is erect and virtual. Where will the image be formed and what will its size be? The lens maker formula for concave lens is given by, 1 f = - (μ1 μ2 − 1) (1 R1 + 1 R2) For a convex lens, R1 is positive and R2is negative. If the focal length is positive, then the lens is said to be converging, and if the focal length is negative, then it is said to be diverging. 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