RAY OPTICS

Kristine Angela R. Revilla

HUB31

Date Submitted: September 21, 2010

Date Performed: September 14, 2010

OBJECTIVE

I. To be able to observe the straight-line propagation of light and to use ray tracing to locate an object

MATERIALS

Optics bench Light source Ray table and base Component holder Slit plate Ray table component holder Viewing screen

BACKGROOUND

A ray is an idealized narrow beam of light. Rays are used to model the propagation of light through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of ray tracing.[1] This allows even very complex optical systems to be analyzed mathematically or simulated by computer. Ray tracing uses approximate solutions to Maxwell's equations that are valid as long as the light waves propagate through and around objects whose dimensions are much greater than the light's wavelength. Ray theory does not describe phenomena such as interference and diffraction, which require wave theory (involving the phase of the wave).

A light ray is a line or curve that is perpendicular to the light's wavefronts (and is therefore collinear with the wave vector). Light rays bend at the interface between two dissimilar media and may be curved in a medium in which the refractive index changes. Geometric optics describes how rays propagate through an optical system.

An incident ray is a ray of light that strikes a surface. The angle between this ray and the

perpendicular or normal to the surface is the angle of incidence.

The reflected ray corresponding to a given incident ray, is the ray that represents the light

reflected by the surface. The angle between the surface normal and the reflected ray is known as

the angle of reflection. The Law of Reflection says that for a specular (non-scattering) surface, the

angle of reflection always equals the angle of incidence.

The refracted ray or transmitted ray corresponding to a given incident ray represents the light that

is transmitted through the surface. The angle between this ray and the normal is known as the angle

of refraction, and it is given by Snell's Law. Conservation of energy requires that the power in the

incident ray must equal the sum of the power in the transmitted ray, the power in the reflected ray,

and any power absorbed at the surface.

If the material is birefringent, the refracted ray may split into ordinary and extraordinary rays,

which experience different indexes of refraction when passing through the birefringent material.

RESULTS AND OBSERVATIONS

Figure 1 shows the results gathered during the experiment. The rays oriented by the light source and slit plate created a triangular pattern in the paper. The point of intersection of the rays was traced and the length or distance from the point of intersection and the middle point of the ray table was measured

Figure 1 Result and Observation Gathered

36cm. the distance of the light source up to the middle of the ray table was also measured to be 36cm, having the percent error of 0.

Ray diagram is very useful in determining the distance or location of the image. The image will be located at the place where the rays intersect.

Practically all objects reflect a certain portion of the light falling on them. The light that is reflected off an object is the color that the eyes see. If a ray of light hits a flat, shiny surface, than it reflects off at the same angle. This means the ray that hits the surface, called the incident ray, which has an angle of incidence  from the normal (an imaginary line perpendicular to the surface at the point where the incident ray encounters it) bounces off as the reflected ray, which has an equal angle of reflection  from the normal.

This is leads to the law of reflection which follows: 

The incident ray, the reflected ray, and the normal to the surface all lie in the same plan, and the angle of reflection,  , equals the angle of incidence,  .

There are two types of reflection. Specular reflection is when parallel light rays strike a smooth, plane surface, such as in the figure below, and reflect off parallel. This is important in determining the properties of mirrors because it shows how much the mirror reflects without distortion. The other type of reflection, diffuse reflection, is when parallel rays strike a rough surface, causing them to reflect in all directions, causing distortion.

In the experiment, Huygen’s principle is evident which states that “Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light. The new wave-front is the tangential surface to all of these secondary wavelets”.

According to Huygens' principle, a plane light wave propagates though free space at the speed of

light,  . The light rays associated with this wave-front propagate in straight-lines. It is also fairly straightforward to account for the laws of reflection and refraction using Huygens' principle.

CONCLUSION

Ray tracing is used to locate the image by tracing the rays produced by the light source. The point of intersection is then the location of the image. This is supported by Huygen’s principle which states that the plane light wave is propagated in a straight manner, thus, continuing the light ray (traces), at some point, they would intersect producing the image.

GUIDE QUESTIONS

1. State and explain the Huygen’s Principle Huygen’s principle states that:

“Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light. The new wave-front is the tangential surface to all of these secondary wavelets”

It recognizes that each point of an advancing wave front is in fact the center of a fresh disturbance and the source of a new train of waves; additionally, the advancing wave as a whole may be regarded as the sum of all the secondary waves arising from points in the medium already traversed. This view of wave propagation helps better understand a variety of wave phenomena, such as diffraction

2. What accounts the percent error between D1 and D2? Explain your answer. On the experiment conducted, the percent error was 0. It is possible to have a 0 percent

error because all of the materials used has a certain measurement, meaning, the angles produced will be equal with each other, thus, the distances of both the image and the light source is the same.