If the equation shows a negative image distance, then the image is a virtual image on the same side of the lens as the object. Also find its magnification. (c) Height of image A'B': 0.7 × 5 = 3.5 cm, i.e., image is smaller than the object. The distance of the object from the lens is 15 cm. Here, Object size, h = + 7.0 cmObject distance, u = - 27 cmFocal length, f = - 18 cm Image distance, v = ? These types of lenses can converge a beam of light coming from outside and focus it to a point on the other side. BO = – u, DI = +v, we get .....(10) Equation (10) is the familiar thin lens formula. Download the PDF Question Papers Free for off line practice and view the Solutions online. However, if one of the surfaces is flat and the other convex, then it is called a plano-convex lens. Hi I am Girish Chandra.Welcome to my youtube channel Chandra Mathematics. If this equation shows a negative focal length, then the lens is a diverging lens rather than the converging lens. (vi) Draw a line A'B', perpendicular to principal axis from B'. This lens is thicker at the centre and gets thinner as we move towards the edges. Converging lens means a convex lens. NCERT Books. So the most common use of the lens is that it helps us to see. Find the position of the image, its nature and size. The lens in the human eyes is the prime example. This lens is thinner at the centre and gets thicker as we move towards the edges. When an object is placed in front of it at a distance shorter than the focal length of the lens, it produces a magnified and erect image of the object on the same side as the object itself. 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. Focal length, f = - 15 cm    [f is - ve for a concave lens], Image distance, v = - 10 cm [Concave lens forms virtual image on same side as the object, so v is - ve]. NCERT Books for Class 5; NCERT Books Class 6; NCERT Books for Class 7; NCERT Books for Class 8; NCERT Books for Class … © It is used in cameras because it focuses light and produces a clear and crisp image. A concave lens of focal length 15 cm forms an image 10 cm from the lens. Class 1 - 3; Class 4 - 5; Class 6 - 10; Class 11 - 12; CBSE. Focal length, f = - 15 cm    [f is - ve for a concave lens]Image distance, v = - 10 cm [Concave lens forms virtual image on same side as the object, so v is - ve]As,                                                          Object distance, u = -30 cm. More generally these are often used in compound lenses used in various instruments such as magnifying devices like microscopes, telescopes and camera lenses. (vi) Draw a line from A to C (centre of the lens), which goes straight without deviation. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. A virtual and erect image of height 2.2 cm is formed behind the mirror (because v is positive) at a distance of 8.6 cm from the mirror. Draw the ray diagram and find the position, size and the nature of the image formed. Lens formula: The lens formula is a mathematical relation between the object distance u, image distance v and focal length f of a spherical lens. It will be found to be equal to 6 cm.Thus, object is placed at a distance of 6 cm × 5 = 30 cm from the lens. A concave lens will always produce diminished, upright and virtual image of the object in front of it. convex lens can converge a beam of parallel rays to a point on the other side of the lens. The major differences between concave and convex lens two are: These are used for a variety of purposes in our day-to-day lives. It is used to correct Hypermetropia or long-sightedness. Magnification, m = -vu= h'h Therefore,  Image size, h' = -vhu                          = -8.6 × 5-20                         = 2.15 ≃ 2.2 cm. BOOK FREE CLASS ; COMPETITIVE EXAMS. We are given a convex mirror. How far is the object placed from the lens? This lens formula is applicable to both the concave and convex lens. This relation is: 1v-1u = 1f In words, we can say that 1Image distance - 1Object distance =1Focal length This formula is applicable to both convex and concave lenses. It is found that CB' = 3.3 cm and A'B' = 0.7 cm. The image is real, inverted and enlarged in size. View Answer NCERT Question 9 - One-half of a convex lens is covered with a black paper. It can form both real and virtual images depending on where the light is coming from. Read about the convex lens along with its use and difference between the concave and convex lens. Draw the ray diagram. But the nature of the image produced by a these lenses depends upon the position of the object. (xi) Thus the final position, nature and size of the image A'B' are:         (a) Position of image A'B' = 3.3 cm × 5 = 16.5 cm from the lens on opposite side. Image size, h' = ? (ii) Draw a convex lens, keeping principal centre (C) on the principal axis. Ans. https://www.zigya.com/share/U0NFTjEwMDUyNjMy. 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