PHYSICS XII roblems For Practice 1 A convex lens of focal
Last updated: 6/7/2023
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PHYSICS XII roblems For Practice 1 A convex lens of focal length 25 cm is placed coaxially in contact with a concave lens of focal length 20 cm Determine the power of the combination Will the system be converging or diverging in nature CBSE D 13 Ans ID diverging 2 A conves lens of focal length 20 cm is placed coaxially in contact with a concave lens of focal length 25 cm Determine the power of the combination Will the system be converging or diverging in nature CBSE D 13 Ans ID converging 3 The radius of curvature of each surface of a convex lens of refractive index 1 5 is 40 cm Calculate its power Ans 2 5 DI 4 Two lenses of powers 10 D and 5D are placed in contact Calculate the power of the new lens Where should an object be held from the lens so as to obtain a virtual image of magnification 27 CBSE OD 08 Ans 5D 10 cm Find the focal length and power of a convex lens which when placed in contact with a concave lens of focal length 25 cm forms a real image 5 times the size of the object placed 20 can from the combination Ans 10 cm 10 D 6 The power of a thin convex lens of glass is 5 D When it is immersed in a liquid of refractive index s it behaves like a divergent lens of focal length 1 m Calculate u of liquid if u of glass 3 2 Am 5 3 7 A compound lens is made of two lenses having powers 15 5D and 55D An object of 3 cm height is placed at a distance of 30 cm from this compound lens Find the size of the image Aru 1 5cm 8 Rays coming from an object situated at infinity fall on a convex lens and an image is formed at a distance of 16 cm from the lens When a concave lens is kept in contact with the convex lens the image is formed at a distance of 20 cm from the lens combination Calculate the focal length of the concave lens Ans 80 cm An equiconvex lens with radii of curvature of magnitude 20 cm each is put over a liquid layer poured on top of a plane mirror A small needle with its tip on the principal axis of the lens is moved along the axis until its inverted real image coincides with the needle itself The distance of the needle from the lens is measured to be 30 cm On removing the liquid layer and repeating the experiment the distance is measured to be 20 cm HINTS LP R 6 Given that the two values of the distance measured represent the focal length values in the two ce calculate the refractive index of the liquid Ans 133 CBSE D 0SC 100 100 25 20 As the power of the combination is negative the system will be diverging in nature 2 Power of convex lensu 100 20 Power of concave lens P Power of the combination P R ID As the power Pis positive the combination will be converging in nature 3 Here 15 40 cm 0 40 m R 40cm 0 40 m P 7 2 15 1 Now 1 1 0 40 0 40 4 P R P 10 5 5D or De 100 cm cm 1 ii m 20 cm As m 20 20 5 Here m 5 20 cm As 2 M 4 5 1D 5 6 01 5 1 H or 20 1 1 1 3 1 50 or 100 25 2 5 D 50 u 10 cm 5D com 4D 1 3 2 1 25 50 10 100 10 cm and P 10 10 D