explain me the three parts of convex lens which is responsible for its reflection
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The Anatomy of a LensRefraction by LensesImage Formation RevisitedConverging Lenses - Ray DiagramsConverging Lenses - Object-Image RelationsDiverging Lenses - Ray DiagramsDiverging Lenses - Object-Image RelationsThe Mathematics of Lenses
If a piece of glass or other transparent material takes on the appropriate shape, it is possible that parallel incident rays would either converge to a point or appear to be diverging from a point. A piece of glass that has such a shape is referred to as a lens.
A lens is merely a carefully ground or molded piece of transparent material that refracts light rays in such as way as to form an image. Lenses can be thought of as a series of tiny refracting prisms, each of which refracts light to produce their own image. When these prisms act together, they produce a bright image focused at a point.
If a piece of glass or other transparent material takes on the appropriate shape, it is possible that parallel incident rays would either converge to a point or appear to be diverging from a point. A piece of glass that has such a shape is referred to as a lens.
A lens is merely a carefully ground or molded piece of transparent material that refracts light rays in such as way as to form an image. Lenses can be thought of as a series of tiny refracting prisms, each of which refracts light to produce their own image. When these prisms act together, they produce a bright image focused at a point.
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10.1 REFLECTION OF LIGHT
A highly polished surface, such as a mirror, reflects most of the light falling on it. You are already familiar with the laws of reflection of light.
Let us recall these laws –
The angle of incidence is equal to the angle of reflection, andThe incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.Activity 1Take a large shining spoon. Try to view your face in its curved surface.Do you get the image? Is it smaller or larger?Move the spoon slowly away from your face. Observe the image. How does it change?Reverse the spoon and repeat the Activity. How does the image look like now?Compare the characteristics of the image on the two surfaces.
The curved surface of a shining spoon could be considered as a curved mirror. The most commonly used type of curved mirror is the spherical mirror. The reflecting surface of such mirrors can be considered to form a part of the surface of a sphere. Such mirrors, whose reflecting surfaces are spherical, are called spherical mirrors. We shall now study about spherical mirrors in some detail.
10.2 SPHERICAL MIRRORS
The reflecting surface of a spherical mirror may be curved inwards or outwards. A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of the sphere, is called a concave mirror. A spherical mirror whose reflecting surface is curved outwards, is called a convex mirror. The schematic representation of these mirrors is shown in Fig. 10.1. You may note in these diagrams that the back of the mirror is shaded.
You may now understand that the surface of the spoon curved inwards can be approximated to a concave mirror and the surface of the spoon bulged outwards can be approximated to a convex mirror.
Before we move further on spherical mirrors, we need to recognise and understand the meaning of a few terms. These terms are commonly used in discussions about spherical mirrors. The centre of the reflecting surface of a spherical mirror is a point called the pole. It lies on the surface of the mirror. The pole is usually represented by the letter P.
Fig.1 Schematic representation of spherical mirrors; the shaded side is non-reflecting.
The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre. This point is called the centre of curvature of the spherical mirror. It is represented by the letter C. Please note that the centre of curvature is not a part of the mirror. It lies outside its reflecting surface. The centre of curvature of a concave mirror lies in front of it. However, it lies behind the mirror in case of a convex mirror. You may note this in Fig.2 (a) and (b). The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the radius of curvature of the mirror. It is represented by the letter R. You may note that the distance PC is equal to the radius of curvature. Imagine a straight line passing through the pole and the centre of curvature of a spherical mirror.
Activity 2CAUTION: Do not look at the Sun directly or even into a mirror reflecting sunlight. It may damage your eyes.Hold a concave mirror in your hand and direct its reflecting surface towards the Sun.Direct the light reflected by the mirror on to a sheet of paper held close to the mirror.Move the sheet of paper back and forth gradually until you find on the paper sheet a bright, sharp spot of light.Hold the mirror and the paper in the same position for a few minutes. What do you observe? Why?
The paper at first begins to burn producing smoke. Eventually it may even catch fire. Why does it burn? The light from the Sun is converged at a point, as a sharp, bright spot by the mirror. In fact, this spot of light is the image of the Sun on the sheet of paper. This point is the focus of the concave mirror. The heat produced due to the concentration of sunlight ignites the paper. The distance of this image from the position of the mirror gives the approximate value of focal length of the mirror.
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Fig.2 (a) Concave mirror
(b) Convex mirror
The reflecting surface of a spherical mirror is by and large spherical. The surface, then, has a circular outline. The diameter of the reflecting surface of spherical mirror is called its aperture. In Fig.10.2, distance MN represents the aperture. We shall consider in our discussion only such spherical mirrors whose aperture is much smaller than its radius of curvature.
Is there a relationship between the radius of curvature R, and focal length f, of a spherical mirror? For spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length. We put this as R = 2f . This implies that the principal focus of a spherical mirror lies midway between the pole and centre of curvature.
A highly polished surface, such as a mirror, reflects most of the light falling on it. You are already familiar with the laws of reflection of light.
Let us recall these laws –
The angle of incidence is equal to the angle of reflection, andThe incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.Activity 1Take a large shining spoon. Try to view your face in its curved surface.Do you get the image? Is it smaller or larger?Move the spoon slowly away from your face. Observe the image. How does it change?Reverse the spoon and repeat the Activity. How does the image look like now?Compare the characteristics of the image on the two surfaces.
The curved surface of a shining spoon could be considered as a curved mirror. The most commonly used type of curved mirror is the spherical mirror. The reflecting surface of such mirrors can be considered to form a part of the surface of a sphere. Such mirrors, whose reflecting surfaces are spherical, are called spherical mirrors. We shall now study about spherical mirrors in some detail.
10.2 SPHERICAL MIRRORS
The reflecting surface of a spherical mirror may be curved inwards or outwards. A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of the sphere, is called a concave mirror. A spherical mirror whose reflecting surface is curved outwards, is called a convex mirror. The schematic representation of these mirrors is shown in Fig. 10.1. You may note in these diagrams that the back of the mirror is shaded.
You may now understand that the surface of the spoon curved inwards can be approximated to a concave mirror and the surface of the spoon bulged outwards can be approximated to a convex mirror.
Before we move further on spherical mirrors, we need to recognise and understand the meaning of a few terms. These terms are commonly used in discussions about spherical mirrors. The centre of the reflecting surface of a spherical mirror is a point called the pole. It lies on the surface of the mirror. The pole is usually represented by the letter P.
Fig.1 Schematic representation of spherical mirrors; the shaded side is non-reflecting.
The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre. This point is called the centre of curvature of the spherical mirror. It is represented by the letter C. Please note that the centre of curvature is not a part of the mirror. It lies outside its reflecting surface. The centre of curvature of a concave mirror lies in front of it. However, it lies behind the mirror in case of a convex mirror. You may note this in Fig.2 (a) and (b). The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the radius of curvature of the mirror. It is represented by the letter R. You may note that the distance PC is equal to the radius of curvature. Imagine a straight line passing through the pole and the centre of curvature of a spherical mirror.
Activity 2CAUTION: Do not look at the Sun directly or even into a mirror reflecting sunlight. It may damage your eyes.Hold a concave mirror in your hand and direct its reflecting surface towards the Sun.Direct the light reflected by the mirror on to a sheet of paper held close to the mirror.Move the sheet of paper back and forth gradually until you find on the paper sheet a bright, sharp spot of light.Hold the mirror and the paper in the same position for a few minutes. What do you observe? Why?
The paper at first begins to burn producing smoke. Eventually it may even catch fire. Why does it burn? The light from the Sun is converged at a point, as a sharp, bright spot by the mirror. In fact, this spot of light is the image of the Sun on the sheet of paper. This point is the focus of the concave mirror. The heat produced due to the concentration of sunlight ignites the paper. The distance of this image from the position of the mirror gives the approximate value of focal length of the mirror.
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Fig.2 (a) Concave mirror
(b) Convex mirror
The reflecting surface of a spherical mirror is by and large spherical. The surface, then, has a circular outline. The diameter of the reflecting surface of spherical mirror is called its aperture. In Fig.10.2, distance MN represents the aperture. We shall consider in our discussion only such spherical mirrors whose aperture is much smaller than its radius of curvature.
Is there a relationship between the radius of curvature R, and focal length f, of a spherical mirror? For spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length. We put this as R = 2f . This implies that the principal focus of a spherical mirror lies midway between the pole and centre of curvature.
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