REFLECTION OF LIGHT

Reflection is when light bounces off an object. If the surface is smooth and shiny, like glass, water or polished metal, the light will reflect at the same angle as it hit the surface. This is called specular reflection.

R E F L E C T I O N O F L I G H T

Light rays are basically wave motions and they are capable of being reflected by an interface in between two mediums. Such interfaces are called Light Reflectors.

The most common Light reflector is the one we use many times a day, which is nothing but a plane mirror. But it is not only a plane mirror reflects light. Even a curved mirror does that though the nature of reflection of light by curved mirrors is different.

Objects can be seen by the light they emit, or, more often, by the light they reflect. Reflected light obeys the law of reflection, that the angle of reflection equals the angle of incidence.
For objects such as mirrors, with surfaces so smooth that any hills or valleys on the surface are smaller than the wavelength of light, the law of reflection applies on a large scale.
All the light travelling in one direction and reflecting from the mirror is reflected in one direction; reflection from such objects is known as specular reflection.
Most objects exhibit diffuse reflection, with light being reflected in all directions. All objects obey the law of reflection on a microscopic level, but if the irregularities on the surface of an object are larger than the wavelength of light, which is usually the case, the light reflects off in all directions.

L A W O F R E F L E C T I O N

The law of reflection states that the angle of incidence is equal to the angle of reflection, or, stated mathematically.

The laws of reflection determine the reflection of incident light rays on reflecting surfaces, like mirrors, smooth metal surfaces, and clear water. Let’s consider a plane mirror as shown in the figure above. The law of reflection states that

The incident ray, the reflected ray and the normal all lie in the same plane
The angle of incidence = angle of reflection

ANGLE OF INCIDENT RAY

is the angle made by the ray incident on the surface from the line which is normal to the plane at the point of incidence.

ANGLE OF REFLECTION

is the angular reflection formed by a reflected ray and a perpendicular to the surface at the point of reflection.

F O R M U L A :

The Angle of incidence always equals the angle of reflection and the distance of image always equals the distance of object are called Angle of reflection formula.

if θi and are the angle of incidence and angle of reflection respectively, then

sin θi = sin θr

θi = θr

When light falls on a surface which is plane, the angle with which the light falls on the surface is equal to the angle with which the light reflects back and the incident ray, reflected ray and the normal ray lies in the same plane.

T Y P E S O F R E F L E C T I O N

There are primarily two types of reflection.

Specular reflection – When light hits the smooth surface, reflected light rays travel in the same direction. For example, in case of mountains covered by lakes, we often see pictures of mountain appearing in lake. This is because lakes have smooth surface that reflects light in same direction and as such perfect image of the mountains is formed.

The angle at which light hits a reflecting surface is called the angle of incidence, and the angle at which light bounces off a reflecting surface is called the angle of reflection.

Diffused Reflection a reflective surface other than mirrors in general have a very rough finish. This may be due to wear and tear such as scratches and dents or dirt on the surface. Sometimes even the material of which the surface is made of matters. All this leads to a loss of both the brightness and the quality of the reflection. In case of such rough surfaces, the angle of reflection when compared between points is completely haphazard. For rough surfaces, the rays incident at slightly different points on the surface are reflected in completely different directions. This type of reflection is called diffused reflection, and is what enables us to see non-shiny objects.

REFLECTION O F LIGHT O N CONCAVE MIRROR ( PLAIN MIRROR)

Concave mirrors are used in certain types of astronomical telescopes called reflecting telescopes. The mirrors condense lots of light from faint sources in space onto a much smaller viewing area and allow the viewer to see far away objects and events in space that would be invisible to the naked eye.

When parallel light rays hit a concave mirror they reflect inwards towards a focal point (F). Each individual ray is still reflecting at the same angle as it hits that small part of the surface

The inside curve of a spoon is an example of a concave mirro
Light rays travel towards the mirror in a straight line and are reflected inwards to meet at a point called the focal point.
Concave mirrors are useful for make-up mirrors because they can make things seem larger. This concave shape is also useful for car headlights and satellite dishes.

The line passing through the center of the sphere and attaching to the mirror in the exact center of the mirror is the principal axis.
The point in the center of the sphere from which the mirror was sliced is known as the center of curvature and is denoted by the letter C. Sometimes a figure of 2F is used at this point.
The point on the mirror’s surface where the principal axis meets the mirror is known as the vertex – V. The vertex is the geometric center of the mirror.
Midway between the vertex and the center of curvature is a point known as the focal point or principal focus ; the focal point is denoted by the letter F.

The following facts are used to construct ray diagrams:

The distance from the vertex to the centre of curvature is called the radius of curvature (represented by R). The radius of curvature is the radius of the sphere from which the mirror was cut.
The distance from the vertex to the focal point is known as the focal length – f. As the focal point is the midpoint of the line joining the vertex and the center of curvature, the focal length is one-half the radius of curvature.

concave1 — any ray travelling parallel to the principal axis on its way to the mirror will pass through the focal point upon reflection.

Curved reflectors are used to make parallel rays of energy emerge from them.

Any ray that passes through the centre of curvature of the mirror will reflect back along its own path because the radius of a circle always hits the edge of the circle at 90 degrees – it hits it normally so the angle of incidence and reflection will both be zero.

To summary the Concave Mirror:

Any incident ray traveling parallel to the principal axis on the way to a concave mirror will pass through the focal point upon reflection.
Any incident ray passing through the focal point on the way to a concave mirror will travel parallel to the principal axis upon reflection.

REFLECTION OF LIGHT ON CONVEX MIRROR (CURVED MIRROR)

When parallel light rays hit a convex mirror they reflect outwards and travel directly away from an imaginary focal point (F). Each individual ray is still reflecting at the same angle as it hits that small part of the surface.

Convex mirrors curve outwards, like the outside of a balloon.
Parallel rays of light strike the mirror and are reflected outwards. If imaginary lines are traced back, they appear to come from a focal point behind the mirror.
Convex mirrors are useful for shop security and rear-view mirrors on vehicles because they give a wider field of vision.

A Convex Mirror was described as a portion of a sphere that had been sliced away. If the outside of the sphere is silvered such that it can reflect light, then the mirror is said to be convex.

The center of that original sphere is known as the center of curvature (C) and the line that passes from the mirror’s surface through the sphere’s center is known as the principal axis. The mirror has a focal point (F) that is located along the principal axis, midway between the mirror’s surface and the center of curvature. Note that the center of curvature and the focal point are located on the side of the mirror opposite the object – behind the mirror. Since the focal point is located behind the convex mirror, such a mirror is said to have a negative focal length value.

A Convex Mirror is sometimes referred to as a diverging mirror due to the fact that incident light originating from the same point and will reflect off the mirror surface and diverge. The diagram at the right shows four incident rays originating from a point and incident towards a convex mirror.

These four rays will each reflect according to the law of reflection. After reflection, the light rays diverge; subsequently they will never intersect on the object side of the mirror. For this reason, convex mirrors produce virtual images that are located somewhere behind the mirror.

The Formation of Images

An image is the location in space where it appears that light diverges from. Any observer from any position who is sighting along a line at the image location will view the object as a result of reflected light. Each observer sees the image in the same location regardless of the observer’s location. As the observer sights along a line, a ray of light is reflecting off the mirror to the observer’s eye.

Light rays originating at the object location are shown approaching and subsequently reflecting from the mirror surface. Each observer must sight along the line of a reflected ray to view the image of the object. Each ray is extended backwards to a point of intersection – this point of intersection of all extended reflected rays is the image location of the object.

On the image above it is a virtual image. Light does not actually pass through the image location. It only appears to observers as though all the reflected light from each part of the object is diverging from this virtual image location. The fact that all the reflected light from the object appears to diverge from this location in space means that any observer would view a replica or reproduction when sighting along a line at this location.

To summary the Convex Mirror:

Any incident ray traveling parallel to the principal axis on the way to a convex mirror will reflect in such a manner that its extension will pass through the focal point.
Any incident ray traveling towards a convex mirror such that its extension passes through the focal point will reflect and travel parallel to the principal axis.

T H E N A T U R E A N D S P E E D O F L I G H T

Light is a transverse, electromagnetic wave that can be seen by humans. The wave nature of light was first illustrated through experiments on diffraction and interference. Like all electromagnetic waves, light can travel through a vacuum. The transverse nature of light can be demonstrated through polarization.

In 1678, Christiaan Huygens (1629–1695) published Traité de la Lumiere, where he argued in favor of the wave nature of light. Huygens stated that an expanding sphere of light behaves as if each point on the wave front were a new source of radiation of the same frequency and phase.
Thomas Young (1773–1829) and Augustin-Jean Fresnel (1788–1827) disproved Newton’s corpuscular theory.

Light is produced by one of two methods

Incandescence is the emission of light from “hot” matter (T ≳ 800 K).
Luminescence is the emission of light when excited electrons fall to lower energy levels
(in matter that may or may not be “hot”).

S P E E D

“In fact I have tried the experiment only at a short distance, less than a mile, from which I have not been able to ascertain with certainty whether the appearance of the opposite light was instantaneous or not; but if not instantaneous it is extraordinarily rapid” – Galileo Galilei, 1638

The speed of light in a vacuum is a universal constant in all reference frames.

The speed of light in a vacuum is fixed at 299,792,458 m/s by the current definition of the meter.
The speed of light in a medium is always slower the speed of light in a vacuum.
The speed of light depends upon the medium through which it travels.The speed of anything with mass is always less than the speed of light in a vacuum.

H O W D O Y O U L E A R N E D T H EM?

In order to learn them our teacher gave us an activity where in you will draw the diagram of rays of : a. Concave Mirror b. Convex Mirror . Where in we don’t have the same places of object. The places of objects are ; Beyond C, At C, Between C and F, At F, and Between F and V (Vertex). At first we didn’t on how to draw the rays because we don’t have the same places of objects but in order to us to understand we helped each other problems. In some part we argue very much because somebody says that is the correct and some say it is wrong. So we gone through our notes where in our teacher discuss about on placing the rays. So at the end of it we learned on how to draw the rays eventhough we don’t have the samw places of objects. In every group activity we will always need your groupmates opinio in irder to learn from them the knowledge that they have.