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CLASS 8 LIGHT PPT.pptx

This document discusses the properties of light reflection. It defines reflection as light bouncing back from a smooth, polished surface. The key points made are: 1) Reflection follows two laws - the angle of incidence equals the angle of reflection, and the incident, normal, and reflected rays all lie in the same plane. 2) Plane mirrors form virtual, laterally inverted images that are the same size and distance from the mirror as the object. 3) Multiple reflections using two or more mirrors can form multiple images, as seen in periscopes and kaleidoscopes.

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CLASS 8 LS 16 LIGHT Deepa Unnikrishnan 1
Deepa Unnikrishnan 2
Mirror & Reflection of light • A mirror is a glass having a shiny or polished surface. • When light falls on a mirror it is reflected back. • Mirror changes the direction of light that falls upon it. 3
REFLECTION • Reflection- The process of bouncing back of light from a smooth and polished surface. NORMAL- THE POINT OF INCIDENCE Deepa Unnikrishnan 4
Incident ray - The ray of light that falls on the surface. Reflected ray - The ray of the light that gets reflected back from the surface. • Normal - It is an imaginary line that is drawn perpendicular to the reflecting surface at the point where the incident ray strikes the surface. (The point of incidence.) • The angle of incidence - The angle that the incident ray makes with the normal. • The angle of reflection - The angle that the reflected ray makes with the normal. Deepa Unnikrishnan 5
TYPES OF REFLECTION Deepa Unnikrishnan 6
LAWS OF REFLECTION • First Law of Reflection The angle of incidence and the angle of reflection are always equal to each other. • The Second Law of Reflection The incident ray, the reflected ray and normal all lie in the same plane. Deepa Unnikrishnan 7
What could happen if I threw the light on the mirror along the normal? • If light is incident on the mirror along the normal, then the angle of reflection and angle of incidence will be same, and they will be equal to zero degree. • The angle of incidence is incident normal to the plane, so light is reflected along the same path. Deepa Unnikrishnan 8
Deepa Unnikrishnan 9
Characteristics of the image by a plane mirror • It has the same height as that of the object. • The distance between the image and the mirror and the object and the mirror is always equal. • The image is erect. (upright). • The image is laterally inverted. • It is a virtual image because it is formed by the apparent intersection of diverging rays. Deepa Unnikrishnan 10
LATERAL INVERSION • When an image is formed in a mirror the, the left side of the object appears at the right side of the image and vice versa. This is called a lateral inversion. Deepa Unnikrishnan 11
LUMINOUS & ILLUMINATED OBJECTS • Illuminated objects - Objects that do not produce light on their own but reflect light. • Luminous objects - Objects which can produce light on their own. Deepa Unnikrishnan 12
MULTIPLE REFLECTION • If more than one mirrors are placed at certain angles to each other, reflection of light happens multiple times between the reflecting surfaces and produce many images. Deepa Unnikrishnan 13
Applications of Multiple reflections in daily- life PERISCOPE KALEIDOSCOPE Deepa Unnikrishnan 14
PERISCOPE- • A Periscope is an instrument that is used to look at objects that are not in the line of sight of the observer. It works on the phenomena of multiple reflection. There are two mirrors that are inclined at an angle 450. It is used in submarines, tanks and bunkers by the soldiers Deepa Unnikrishnan 15
Kaleidoscope- • It is a device that works on the phenomena of multiple reflections with the help of three plane mirrors inside it. We can look into the Kaleidoscope from one end and the light enters into the Kaleidoscope from the other end. When the light falls upon these objects in the Kaleidoscope, multiple reflections of these objects are created in the three Mirrors. This results in the formation of beautiful and colourful patterns. Deepa Unnikrishnan 16
DISPERSION OF LIGHT • The sunlight is white in colour however this white light • The white light consists of seven colours namely VIBGYOR (violet, indigo, blue, green, yellow, orange and red). • This arrangement of seven colours of a white light is called as Spectrum. • However, due to the reflection of light, the seven colours can split and be seen as separate colours rather than a single white light. • This phenomenon of the splitting of light into its constituents is called Dispersion of light. Deepa Unnikrishnan 17
Examples of dispersion of light: • Formation of rainbow due to the dispersion of white light through the water droplets. • Passing of Sunlight through a prism • Dispersion of light through the soap Bubbles • Dispersion of light on the CDs Deepa Unnikrishnan 18
THE HUMAN EYE • PUPIL- Small opening in the iris. The size of the pupil is controlled by the iris. • CONVEX LENS- Behind the pupil there is a lens which focuses light on the retina. • RETINA- Back layer contains several nerve cells. There are two kinds of cells– • (i) cones, which are sensitive to bright light and (ii) rods, which are sensitive to dim light. Cones sense colour. • OPTIC NERVE- Sensations felt by the nerve cells are then transmitted to the brain. • BLIND SPOT - At the junction of the optic nerve and the retina, there are no sensory cells, so no vision is possible at that spot. This is called the blind spot. CORNEA- Transparent front part of the eye. IRIS- A dark muscular structure called located behind the cornea. It gives distinctive colour to the eye and also controls the amount of light entering into the eye. It reduces the size of the pupil when there is exposure of bright light and increases the size of the pupil when there is dim light. Deepa Unnikrishnan 19