Reflection of Light PDF - Physics Revision Notes
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This document covers essential concepts of light reflection, ideal for students studying physics. It explains the laws of reflection, various reflection types, and the principles behind plane mirrors and lateral inversion, enhancing understanding of optical phenomena.
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Okay, here's the conversion of the image into a structured markdown format: ### Reflection of Light We see objects around us because light is absorbed and re-emitted from them. In some objects, such as surfaces of metal, almost all the light is re-emitted; therefore, they appear shiny, and our ref...
Okay, here's the conversion of the image into a structured markdown format: ### Reflection of Light We see objects around us because light is absorbed and re-emitted from them. In some objects, such as surfaces of metal, almost all the light is re-emitted; therefore, they appear shiny, and our reflection can be seen on them. Mirrors re-emits the maximum light falling on it, so we see ourselves very clearly in a mirror. When light falls on any opaque surface, the light is absorbed and partially re-emitted back to the same medium. Since only part of the light is re-emitted, we do not see our reflection on opaque, dull surfaces. The bouncing back of light from opaque objects is known as the reflection of light. **Laws of Reflection** When a ray of light falls on the mirror, the light ray gets reflected. The incident light on the mirror is called the incident ray and the reflected light is called the reflected ray. The line drawn perpendicular to the plane mirror at the point of incidence is called the normal. The angle measured between the incident ray and the normal is called the angle of incidence and the angle measured between the reflected ray and the normal is called the angle of reflection. **First law of reflection:** The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane. **Second law of reflection:** The angle of incidence is equal to the angle of reflection **Diagram Description:** An illustration shows a ray of light hitting a reflective surface. The incident ray, reflected ray, and normal are labelled. The angles of incidence (i) and reflection (r) are equal and shown. It is the "Reflection of light" and there are labels for: source of light, incident ray, angle of incidence, normal, surface mirror reflecting plane, angle of reflection, reflected ray, eye. *i* = *r*. **Regular and Diffused Reflections** There are two types of reflection-regular and diffused reflections. When a parallel beam of light falls on a smooth, shiny surface, the light gets reflected into the same medium. The reflected rays, after reflection, are all parallel to each other. This type of reflection is called regular or clear reflection. When a parallel beam of light falls on a rough surface, the light gets reflected into the same medium. The reflected rays, after reflection, scatter in different directions. This type of reflection is called diffused reflection. **Diagram Description:** *Figure 15.2 (a):* depicts parallel incident rays hitting a smooth reflecting surface and reflecting as parallel rays. Labelled: Incident rays, Reflected rays. *Figure 15.2 (b):* shows parallel incident rays hitting a rough surface and scattering in different directions. Labelled: Incident rays, Reflected rays. --- It is important to note that in both clear and diffused reflections, the laws of reflection hold true. **Reflection on a Plane Mirror** Suppose we place a small object in front of a plane mirror, as shown in Figure 15.3. Rays of light falling on the object is reflected in different directions. When some of these rays fall on the plane mirror, they get reflected, depending on the angle of incidence. When we look at the reflected ray, they seem to diverge from a point behind the mirror. (Note that the light rays do not come from this point, they only appear to come from this point. Therefore, the rays are indicated by the dotted lines.) This is the point where the image of the object is formed. Like this for every point on the object, there is an image point formed behind the mirror. All these points form the image of the object behind the mirror. One can also notice that the size of the image is equal to the size of the object, and that the distance of the object in front of the mirror is equal to the distance of the image formed behind the mirror. **Diagram Description:** *Figure 15.3:* illustrates image formation by a plane mirror with virtual image and object shown. Labels: Object, Virtual image, Plane mirror *Figure 15.4:* Depicts Lateral inversion **Lateral Inversion** Consider a man standing in front of a plane mirror. You will notice that if he pretends to shake his right hand in front of the mirror, then its image in the mirror appears as if he is shaking his left hand. This left-right inversion of the object is known as lateral inversion. You must have noticed that the word 'AMBULANCE' in front of an ambulance is written laterally inverted. This is done so that the driver of the vehicle in front of the ambulance can easily read the correct word on his rear-view mirror and give way to the ambulance. **Real World - Polished Surfaces** The picture shows how polishing can increase the reflectivity of a metal surface. When we buy a new steel vessel or a new steel plate, we are able to see our reflection in it very clearly. This is because a new steel plate is polished. However, after repeated usage, the surface becomes dull and rough. The reflection now becomes diffused. **Multiple Reflection** Have you seen mirrors placed parallel to each other in the trial rooms of a clothes showroom or in a hair salon? We see infinite multiple images of oneself. When two or more mirrors are placed in such a way that light from an object undergoes multiple reflection in them, we can observe multiple images of the object. **Kaleidoscope** The kaleidoscope is a simple device that uses the principle of multiple reflection to create beautiful and colourful patterns the construction of a kaleidoscope is simple. Three plane mirrors are stuck together with tape so as to form a triangular shaped prism. is When colour beads are enclosed at the end a transparent sheet and seen through the eyepiece at the other end, --- A periscope is a device that is used to see objects located at a higher level. In periscope, two mirrors are placed parallel to each other, each being at an angle 45° to the corners. It is commonly-used in submarines and by the military for spying. Here's the completed table. | | | | | :---- | :------------- | :---------- | | 1\. | opaque | no | | 2\. | reflected | same | | 3\. | same | plane | | 4\. | diffused | | | 5\. | seven | | **REFRACTION OF LIGHT** Figure 15.9 shows a pencil in a cup of water. The pencil appears to be broken. Why does this happen? This happens because of refraction. The phenomenon in which light passing from one optical medium to another deviates from its path or changes its direction is called refraction. It is found that when light passes from air into water, it bends towards normal and when it passes from glass to air, it bends away from the normal. This is because light slows down nan optically denser medium. When light passes from an optically rarer redium (air) to an optically denser medium (glass), it bends towards the nomal. When it passes from an optically denser medium (glass) to an optically rarer medium (air), it bends away from the normal. Therefore, refraction is defined as a phenomenon in which a light ray, passing obliquely from one optical medium to another optical medium, deviates from its path Figure 15.11 Formation of a rainbow due to dispersion of light **Dispersion** Most of us have seen rainbows in the sky. A rainbow is formed when the white light from the sun gets split up into its seven constituent colours This splitting up of white light into its constituent colours is known as dispersion. Dispersion of white light can be obtained by using a prism. This was demonstrated by Sir Isaac Newton and was published in his book 'Opticks' in the year 1704. **Figure 15.10** *(a)* Incident ray, Refracted ray. Glass Air: *If = 30° r = 19.5°* *(b)* Incident ray, Refracted ray. Air Glass: *If = 30° r = 19.5°* --- **The Human Eye** The most remarkable optical instrument is considered to be the human eye. The light from the object that we see enters the eye and is interpreted by the brain. Here, light energy is converted to electrical impulses that is sent from the eye to the brain to interpret the image of the object seen. The human eye consists of many parts as shown in Figure 15.12. The foremost part of the eye, through which light enters the eye, is a transparent cover called the **cornea**. The cornea protects the eye and about 70% of the focus of light falling on the eye is done by the cornea The cornea is shaped by a fluid called the **aqueous humor.** Diagram describing all of the parts of the human eye including: ciliary muscles, cornea, iris, pupil, lens, aqueous humour, retina, macula, blind spot, salpingiony ligaments, optic nerve, vitreous humour. The light then enters an opening called the pupil. The size of the pupil is controlled by the *iris*. By controlling the size of the opening, the amount of light entering the eye is controlled. The iris also gives the colour to the eye. The light then passes through the *lens*. The lens focuses the light onto the *retina.* The retina is the screen at the back of the eye on which the focused image of the object is formed. The retina has cells called rods and cones (named because of the shape of the cells). The rods detect the intensity of light, while the cones detect the colour There are many animals that have only rods and no cones in their retina. Therefore, they see the world in black and white. The retina detects the light and sends the signal to the brain through the *optic nerve*. There is a jelly-like fluid that fills the eye and gives shape to the eye. This is the *vitreous humour.* **Real World**- Persistence of vision: The phenomenon by which there is a retention of a visual image of an object by the brain even after the source of light is removed from the eye is known as *persistence of vision*. The brain retains the image for one sixteenth of a second. A simple example is a flip book, where if the pages are flipped fast enough, it gives the illusion of a smooth motion. That persistence of vision is utilized in motion picture, where the number of frames per second is more than 16 frames per second. At this frame rate, the eye sees the images as an illusion of smooth motion. Today's motion pictures flash the images at a rate of 24 to 30 frames per second. **DEFECTS OF THE EYE** If we do not take proper care of our eyes, there can arise some defects in our normal vision. A normal eye can see from a distance of 25 cm to infinity. However, with improper reading habits, watching television up-close or reading books by keeping it close to our eyes, we strain our eyes and this can lead to defects. The common eye defects are *myopia* or *short-sightedness* and *hypermetropia* or *long-sightedness.* **Myopia:** In this defect, a person can see nearby objects, but cannot see distant objects clearly. This defect can be corrected by using concave lens of appropriate power. **Hypermetropia:** In this defect, a person cannot see nearby objects clearly, but can see faraway objects. This defect can be corrected by using convex lens of appropriate power **Figure 15.13 (a): Myopia** Shows a short-sighted eye where image focuses in front of the retina. **Figure 15.13 (b): Myopia corrected by concave lens** Shows image focusing on the retina. **Figure 15.14 (a): Hypermetropia** Shows an eye where focus is past the retina. **Figure 15.14 (b): Hypermetropia corrected by convex lens** Shows an image focusing on the retina