Mirror Module: Light, Reflection, Refraction | PDF

**CHAPTER 1: LIGHT RAYS** ***WHAT IS LIGHT?*** - The study of light probably began before the dawn of history. However, ***the earliest surviving records are from the ancient Greeks dating back to the 5^th^ and 6^th^ century B.C.E.*** It is not surprising that light and vision were t...

**CHAPTER 1: LIGHT RAYS** ***WHAT IS LIGHT?*** - The study of light probably began before the dawn of history. However, ***the earliest surviving records are from the ancient Greeks dating back to the 5^th^ and 6^th^ century B.C.E.*** It is not surprising that light and vision were tied closely together in these early theories. - ***Socrates and Plato*** theorized that light traveled from person's eyes to the objects one saw while the followers of ***Pythagoras*** believed that light was made up of particles emitted from the objects rather than from the eyes. - The Greek philosopher ***Aristotle*** (4^th^ B.C.E)) put forth the theory that light moved as a wave, like water ripples on water. Much later, around 1500, ***Leonardo da Vinci*** noted similarities between the behavior of sound and light. He too attributed a wave nature to light. - In the 17^th^ and 18^th^ centuries, the particle-wave debate became more heated. Most scientists accepted a theory put forth by ***Isaac Newton***. Postulating that light moved as a stream of particles, Newton devised a theory which accounted for most of the known behaviors of light, including refraction, reflection and color. - Refusing to accept Newton's, Dutch scientist ***Christian Huygens*** showed that a wave theory could also account for Newton's observations. In addition, the wave model explained small number of experiments which indicated that, like sound waves, light exhibit refraction. However, the particles theory prevailed well into the 19^th^ century. - In 1801, ***Thomas Young*** provided the first clear evidence that light exhibited interference. A short time later the French physicist ***Augustin Fresnel*** proposed a comprehensive mathematical wave theory. Supported by a number of detailed experiments, Fresnel's theory successfully accounted for all the observed behaviors of light. By the middle of 19^th^ century, opinion had swung towards support of the wave theory of light. - Possibly the most important development in the wave theory of light was the work of ***James Clerk Maxwell***. Maxwell believed that light was a wave produced when electric forces accelerated charged particles within atoms. This kind of wave, and the energy it carried, was termed electromagnetic radiation. The entire range of electromagnetic radiation is called electromagnetic spectrum. - ***Scientist now agree that neither a wave model nor a particle model can explain all properties and behaviors of light.*** **TRANSMISSION OF LIGHT** - The currently accepted value for the speed of light in a vacuum is: ***3 x 10^8^ m/s.*** - A ***ray***, in physics, is the path taken by light energy. It is often represented by a solid line with an arrow indicating the direction of travel of the light energy. A ***beam of light*** is a stream of light rays, and it is represented by a number of rays. The rays may be converging, diverging or parallel. - The amount of light energy that radiates per second per unit area is called ***illumination***. ***The unit for illumination, E, is lux.*** ***Characteristics of an image:*** 1. Orientation (erect or inverted) 2. Size (larger, smaller or same size) 3. Type (real or virtual) ***Two Kinds of Image Formed on a screen*** 1. ***Virtual image***- an image formed not by the actual rays or light but by the extensions of the reflected rays. 2. ***Real image***- an image formed by the actual convergence of light rays upon a screen. - Light travels in a straight line until it strikes an object. If the object is ***opaque***, like a piece of wood, the transmission is interrupted. If the object is ***transparent***, like a piece of glass, light passes through. Terms used when describing the reflection of light: - ***Incident ray***- the ray approaching the mirror. - ***Reflected ray***- the ray reflected by the mirror. - ***Point of incidence***- the point where the incident ray strikes the mirror. - ***Normal line***- the construction line drawn at right angles to the mirror at the point of incidence. - ***Angle of incidence***- the angle between the incident ray and the normal line - ***Angle of reflection***- the angle between the reflected ray and the normal line **CHAPTER 2: REFLECTION AND MIRRORS** **IMAGE IN A PLANE MIRROR** Characteristics of an image in a plane mirror 1. It is the same size as the object. 2. It is vertically erect. 3. It is virtual. 4. Reversed along the normal in the mirror. 5. Located at the same perpendicular distance behind the mirror as the object in front of it. ***LAWS OF REFLECTION*** - The incident ray, the reflected ray and the normal all lie in the same plane. - The angle of incidence and the angle of reflection are equal. Applications: 1. Plane mirrors in cameras -- used in the viewfinders of many cameras. 2. Periscope -- a simple periscope consists of 2 plane mirrors facing each other, mounted at an angle of 45^0^ to the horizontal and vertical planes. 3. Theatrical effects -- for illusion. 4. See-Through mirrors **IMAGE IN A CURVE OR SPHERICAL MIRRORS** ***Two Kinds of Spherical/Curved Mirror:*** 1. ***Concave Mirror***- if the reflecting surface is the inner one. Also known as a converging mirror. Can also form a real and virtual image. 2. ***Convex Mirror***- if the reflecting surface is the outer one. Also known as diverging mirror. Never form a real image, instead it forms virtual, erect and reduced in size and the image is located at behind the mirror. ***Features/Parts of a Spherical Mirror:*** 1. ***center of curvature (C)***- the center of a space of which the mirror is a part. 2. ***aperture***- the diameter of a mirror. 3. ***Vertex (V)*** -the center of the mirror. 4. ***Principal axis*** - the line drawn through the center of curvature of the vertex. 5. ***Secondary axis***- any other drawn through the center of curvature. 6. ***Focus (F)*** - the point between the center of curvature and the vertex. The point where the light rays meet. 7. ***Focal length (f)*** - the distance from the vertex to the focus. It is ½ of the distance from the vertex of curvature to the focus.  **IMAGE FORMATION BY CURVED MIRRORS:** To create an image formed by a concave mirror, we may place a ray diagram. 1. The incident ray parallel to the principal axis is reflected through the focus. 2. The incident ray that passes through the focal point is reflected parallel to the principal axis. 3. The ray that passes through the center of curvature passes back along the same path. - The intersection of the reflected rays indicates the location of the image. **CHAPTER 3 REFRACTION OF LIGHT** Terms commonly used in refraction of light rays: - ***Incident ray*** - ***Angle of incidence*** - ***Angle of refraction*** -- the angle between the refracted ray and the normal.  ***LAWS OF REFRACTION*** 1. The incident ray and the refracted ray are on opposite sides of the normal ray at the point of incidence, and all three are in the same plane. 2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant (also known as Snell's Law by Willebrod Snell). - ***The speed of light is greatly affected by the medium's optical density***. When light passes from a less dense to a denser medium, it slows down. The ray bends towards the normal line. - Light is refracted only when it strikes a boundary at an angle from the normal. ***When light strikes a boundary at right angles, it does not refract.*** - Sometimes, light cannot get out of the boundary between two transparent media. This leads to an interesting phenomenon known as total internal refraction. Example: sparkling of diamond. **LENSES** - Lenses are smoothly curved transparent materials usually made of glass or plastic. It has one or two curved surfaces which form a common boundary between an optically dense medium and a less dense one. Two kinds of lenses 1. ***Convex or converging lens*** -- the parallel rays are refracted upon passing through the lens towards the thicker part and converge on the other side. 2. ***Concave or diverging lens*** -- the parallel rays are refracted towards the thicker part of the lens but since the thicker part of this type is at its edges, the rays spread out or diverge.  Terminologies associated with the lens: - ***Principal axis*** -- imaginary line passing through the center of the lens and at right angle. - ***Lens axis*** -- other imaginary line which bisects the symmetrical lens into two. - Lenses with two symmetrical curved faces like biconvex and biconcave lenses have two focal points.  ***LOCATING THE IMAGE GRAPHICALLY*** At least two rays can be used to locate the image. These rays are the following: 1. The ray from the object parallel to the principal axis of the lens. This ray passes through the focus after refraction in the case of convex lens. In the case of concave lens, the refracted ray seems to come from the focus. 2. The ray passing through the center of the lens. This ray is not refracted. It goes straight. This is true to both concave and convex lenses. **VISION DEFECTS AND CORRECTIVE LENSES**  1. ***Nearsightedness and Correction*** - The inability of the eye to focus on distant objects is known as nearsightedness or myopia. The nearsighted eye has no difficulty viewing nearby objects, but its problem to view distant objects. - To correct a nearsighted eye, a diverging lens is needed. A diverging lens will serve to educe the total refracting power of eye lens. 2. ***Farsightedness and Correction*** - The eye's inability to focus on nearby objects is known as farsightedness or hyperopia. The farsighted eye has no difficulty viewing distant objects. But the ability to view nearby objects requires a lens shape which will the farsighted eye is unable to assume. - The correction for the farsighted eye centers on assisting the eye lens in refracting the light. This is done by using a converging or convex meniscus lens.