12/26/2023 0 Comments Regular reflection definition physics![]() Rules for the formation of images by Convex Lens: (ii) Second Focal Length (F2): The distance of second principal focus (F2) of the lens from the optical centre ‘O’ of the lens is called second focal length of concave lens. (i) First Focal Length (f1): The distance of first principal focus (F1) of the lens from optical centre ‘O’ of the lens is called first focal length of concave lens. Since a concave lens has two principal foci, so it has two focal lengths, known as : first focal length (f1) and second focal length (f2). It is usually denoted by the letter ‘f ‘. The distance of the principal focus (F1 or F2) from the optical centre ‘O’ of a lens is called its focal length. It is generally denoted by the letter (F2), as shown in the figure (b). (ii) Second Principal Focus (F2): The second principal focus (F2) of a concave lens is the position of image point on the principal axis of the lens, when the object is situated at infinity. It is usually denoted by the letter ‘F1’, as shown in the figure (a) (i) First Principal Focus (F1) : The first principal focus (F1) of a concave lens is the virtual position of a point object on the principal axis of the lens, for which the image formed by the concave lens is at infinity. Since the light rays do not actually pass through the focus (or foci) of a concave lens, therefore, a concave lens has a virtual focus. The two foci of a lens are at equal distances from the optical centre, one an either side of the lens. However a concave lens has two spherical surfaces and hence it has two principal foci or two focal points which are usually denoted by the letters ‘F1’ and ‘F2’ and are known as the first principal focus ‘F1’ and the second principal focus ‘F2’. It is usually represented by the letter ‘F’. The principal focus of a concave lens is a point on its principal axis from which light rays parallel to the principal axis, appear to diverge after refraction by the lens. Since there are two centres of curvature, we may represent them as C1 and C2.Īn imaginary straight line passing through the two centres of curvature of a lens is called its principal axis. The centre of curvature of a lens is usually represented by the letter C. ![]() The centres of these spheres are called centres of curvature of the lens. Each of these surfaces form a part of a sphere. In the figure (a), (b) ‘AB’ is the diameter of the circular outline of the lens which represents aperture of the lens or we can say that aperture is the actual refracting surface of the lens.Ī lens, either a convex lens or concave lens, has two spherical surfaces. The effective diameter of the circular outline at a spherical lens is called its aperture. A ray of light passing through the optical centre at a lens goes undeviated. It is usually represented by the letter O. The centre point of a lens is known as its optical centre. SOME IMPORTANT TERMS ASSOCIATED WITH SPHERICAL LENSES The angle between the reflected ray and normal to the surface is called the angle of reflection. The angle of reflection is the angle made by the reflected ray with the normal at the point of incidence. In this case only the surface is visible and not the image. Laws of reflection are not valid in irregular reflection. Such a reflection is known as irregular reflection or diffused reflection or scattering of light. When the reflecting surface is rough, the parallel rays falling on it are reflected in different directions as shown in the figure. It is the regular reflection that makes the object visible. The laws of reflection are valid only in regular reflection. Then it is known as a regular reflection. the reflected light goes in one particular direction as shown in the figure. mirror, the parallel rays falling on it are reflected parallel to one another i.e. ![]() ![]() When the reflecting surface is smooth and well polished, e.g. ![]()
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