/Width 71 In general, the lenses come in two shapes: convex (curved outward) and concave (curved inward). The power of a lens is specified as the inverse of the focal length in meters, or D =\[\frac{1}{F}\], where D is the power in dioptres. endobj In other words, a lens of small focal length is said to have greater power. A lens formula may be defined as the formula which gives the relationship between the distance of image (v), distance of object (u), and the focal length (f) of the lens. /ColorSpace/DeviceRGB New Cartesian Sign Conventions for refraction of light, Rules for Obtaining Images by Spherical Lenses. /Filter/FlateDecode << Draw the ray diagram. An object 5 cm high is held 25 cm away from a converging lens of focal length 20 cm. Is lens formula applicable only for convex lens? >> %���� endobj power of +3.00 Lens surface power can be found with the index of refraction and radius of curvature. >> Define lens formula. The formula for surface power is Ds = (u-1)/r, where u is the index of refraction and r the radius of curvature in meters. /OP true /Length 2355 /Subtype/Image A concave lens of focal length 15 cm forms an image 10 cm from the lens. The dioptre is the unit for a measure of the refractive index of a lens. << Draw the ray diagram and find the position, size and nature of the image formed. /Type/XObject Power of Lens … Test Your Understanding and Answer These Questions: A lens formula may be defined as the formula which gives the relationship between the distance of image (v), distance of object (u), and the focal length (f) of the lens. 2 0 obj Dioptre formula is used to calculate the optical power of a lens or curved mirror. For example, if the focal length of a lens is 20 cm, converting this to meters, we get 0.2 m To find the power of this lens, take the reciprocal of 0.2, and we get 5. Is lens formula applicable only for convex lens? >> %PDF-1.4 /Height 46 A lens is said to be of greater power if it diverges or converges a beam of light more strongly by focusing them closer to the optical centre. /BitsPerComponent 8 So for example, if a lens has a focal length = 100 cm = 1 m Power would be= 1 D X�ݙ�WSI���9g��M� ;��[�A��M�idIBd �]HXe�ЄfiY�ɞ0��h@@�"3���8������ｷ�n�0GKh#�L}�Lk��9Qł6Y͞�bNV0&*�匉J��^+Y���� �&���B�H�͎�b�&^[��/-|������O�^��3h��9��2��r�2���f6��zNR��l��Q�An����{�M�\6�ͥu�}�ѷ��y¸����A�->�~����l�h���/.fb3�=��$�.�����E|>��sI�2>K9=�A���VEI/�Kt�qz''Ť��J����-&��"���$�T�S����M��jm卟��D���[���4���3!��b�)��(a��Z���s�!P%9��8T��A-tS. Lens Formula and Magnification - Lens Power Lenses, both converging and diverging, are the marvels of optical physics that use the ability of these media to refract, reflect, or bend light rays. A concave lens of focal length 15 cm forms an image 10 cm from the lens. /OP false 1 0 obj 3 0 obj An object 5 cm high is held 25 cm away from a converging lens of focal length 20 cm. << /Type/ExtGState /OPM 1 How far is the object placed from the lens? The lens formula is applicable both in convex lenses and concave lenses. /Type/ExtGState stream Draw the ray diagram and find the position, size and nature of the image formed. Therefore, the power of this particular lens if 5D. The power of a lens is defined as the ability of the lens to converge or diverge a beam of light falling on it. It may be written as: Where, v = Distance of image from optical centre of lens u = Distance of object from optical centre of lens and f = Focal length of lens. Formula of power of a lens is : Here P(Power) is expressed in ‘D’(Dioptre) and Focal length is expressed in ‘m’(meter).
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