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Notes ch 15, , What is light?, → It is a natural agent which stimulates sight and makes things visible., → It travels in a straight line., → It is a form of energy., What is an image?, → It is an impression of the object created by the light on the mirror., → Distance between image and mirror and, the object and mirror is always, same., Types of image, (i) Erect image: When the image is formed the same side up as that the, object., (ii) Inverted image: When image is formed upside-down compared to object., → If we increase or decrease the distance between the object and the mirror, then the distance between the image and the mirror are also increase or, decrease., Left-right inversion of image, Image formed by the mirror is always left-right inverted which means the right, side of the object appears as the left side of image and the left side of the, object appears at the right side of the image.
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Reflection of light, (i) Incident ray: The ray which falls on the reflecting surface is called an, incident ray., (ii) Reflected ray: The ray that gets reflected back from the reflecting surface is, called reflected ray., ., , Laws of reflection, •, , •, •, , The ray of light that strikes a reflecting surface is called as the, incident ray and the ray that gets reflected back is called the, reflected ray, The imaginary line that is perpendicular to the reflecting surface at, the point of incidence is called the normal, Angle of incidence ∠i is the angle between the incident ray and the, normal. Angle of reflection ∠r is the angle between the reflected ray, and the normal.
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Law of Reflection states that the angle of incidence ∠i is always, equal to the Angle of reflection ∠r (∠i=∠r). The angle of incidence,, angle of reflection and the normal all lie on the same plane, Plane Mirror, •, , Characteristics of the image formed by a plane mirror:, •, •, •, •, , The image formed by a plane mirror is always virtual and erect., The image undergoes lateral inversion., The size of the image formed by a plane mirror is the same as that of the object., The distance of the object from the mirror is equal to the distance of the image from, the mirror, that is, image distance is equal to object distance., , Spherical Mirrors:, Unlike plane mirrors that are flats, spherical mirrors have curved surfaces. Spherical Mirrors, are of two kinds:, •, •, , Concave mirror, Convex mirror, , Concave mirror: A concave mirror is a spherical mirror whose reflecting surface is on the, inner side. It is also known as a converging mirror, as a parallel beam of light after reflection, from a concave mirror converges at a point., , Uses of Concave Mirrors, •, •, •, , To see the large image of teeth of a patient, concave mirrors are used by the, dentist., In torches, headlights of vehicles and searchlights to get a strong, straight, beam of light, etc., concave mirrors are used as reflectors., To see a large image of the face, then concave mirrors are used as shaving, mirrors.
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Convex mirror: A convex mirror is a spherical mirror whose reflecting surface is on the, outer side. It is also known as a diverging mirror, as the parallel beam of light after reflection, from a convex mirror diverges., , Uses of Convex Mirrors, •, , •, , To see the traffic at the rear side or backside on the road, convex mirrors are, used as rear view mirrors or side view mirrors in vehicles such as cars,, scooters, buses, etc., Big convex mirrors are used as shop security mirrors. By installing a convex, mirror in the shop, the shop owner can keep an eye on the customers., , Image Formed by Lenses, Since a lens is a piece of transparent glass bound by the two spherical surfaces., Lenses are transparent so that light can pass through lenses. Lenses are of two, types:, •, •, , Convex lens, Concave lens, , Convex Lens (Converging Lens), The convex lens is the lens which is thicker in the middle than at the edges. A beam of
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parallel rays of light falls on a convex lens from the left side. After passing through the, convex lens, the beam of parallel rays of light converges at a point as shown in the figure, given below. Hence, a convex lens is a converging lens., , Uses of Convex Lenses, •, •, , Convex lenses are used as a magnifying glass., In the manufacturing of spectacles, camera, microscope, telescope and, binoculars, convex lenses are used., , Concave Lens (Diverging Lens), A concave lens is a lens which is thinner in the middle than at the edge. A parallel beam of, light falls on a concave lens as shown in the figure. After passing through the concave lens,, the rays of light are diverging (or spreading out)., , Uses of Concave Lenses, •, •, , In order to see the image of the person standing outside, concave lenses are, used in the peepholes in the door of hotel rooms., Concave lenses are used in making spectacles, Dispersion of Light, In the year 1665, Newton discovered by his experiments with glass prisms that, white light (like sunlight) consists of a mixture of lights of seven colours., Newton found that if a beam of white light is passed through a glass prism,
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then the white light splits to form a band of seven colours on a white screen., The band of seven colours formed on a white screen, when a beam of white, light is passed through a glass prism, is known as a spectrum of white light., The seven colours of the spectrum are Red, Orange, Yellow, Green, Blue, Indigo, and Violet.
