PHY385 Module 6

                                                                    Student Guide

 

Concepts of this module

External reflection. Spherical mirror equation.

Total internal reflection.

Colors formation.

Quiz

 

    

 

Activity 1 - External reflection. Spherical mirror equation.

 

EQUIPMENT NEEDED:

- Optics Bench

- Light Source

- Component Holder (3)

- 50 mm F. L. Spherical Mirror

- Viewing Screen

- Crossed Arrow Target.

Parallel rays can be brought to a focus by a reflective paraboloid of revolution. For rays close to the optical axis, a paraboloid of revolution can be approximated by a spherical surface. In this activity, you will investigate an image created by a concave spherical mirror and verify the mirror equation.

 

 

 

 

 

 

 

 

 

 

 

a)      Set up the equipment as shown in Fig.1, with the concave side of the mirror facing the Light Source. The Viewing Screen should cover only half the hole in the Component Holder so that light from the filament reaches the mirror.

b)      Adjust the position of the mirror until there is a well focused image of the crossed arrow target on the viewing screen.

c)      Make measurements of so and si for four or five values of so. Show the table of measured values.

d)      Plot 1/so versus 1/ si and find the best fit line.

e)      Using the fitter, calculate the focal length of the spherical mirror.

f)        Rearrange the experiment by removing the Viewing Screen and observing the image on the surface of the crossed Arrow Target. Find the focal length of the mirror from this measurement.

g)      Compare the two experiment results and the given value for f . Which method of measurement is more accurate? Why?

h)      From this, what do you expect is the radius of curvature of this mirror?

Activity 2 - Total internal reflection.

 

EQUIPMENT NEEDED:

-Optics Bench

-Light Source

-Ray Table and Ray Table Base

-Component Holder

-Slit Plate

-Slit Mask

-Cylindrical Lens

-Ray Table Component Holder

-Viewing Screen.

 

Set up equipment as shown in Fig. 2, so a single light ray is incident on the curved surface of the cylindrical lens.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


a)      Set the Ray Table so the angle of incidence of the ray striking the flat surface of the lens (from inside the lens) is zero-degrees. Adjust the Ray Table Component Holder so the refracted ray is visible on the Viewing Screen.

b)      Slowly increase the angle of incidence on the interface acrylic/air. As you do, watch the refracted ray on the Viewing Screen. Notice that not all of the light in the incident ray is refracted. Part of the light is also reflected. From which surface of the lens does reflection primarily occur?

c)      Are the angles of the reflected ray consistent with the law of reflection?

d)      How does the intensity of the reflected and refracted rays vary with increasing the angle of incidence?

e)      At what angle of incidence is all light reflected?

f)        Measure and calculate the critical angle for the total internal reflection.

g)      What happens with the incident ray if you continue increasing the incident angle?

h)      Does the internally reflected ray obey the law of reflection?

 

    

 

Activity 3 - Colors formation

 

Early investigators assumed that light, in its purest, simplest form is white; and that refractive materials alter the characteristics of the white light to create the various colors. Sir Isaac Newton was the first to show that light, in its simplest form, is colored; and that refractive materials merely separate the various colors which are the natural constituents of white light. He used this idea to help explain the colors of objects.

 

EQUIPMENT NEEDED:

- Same as in Activity 3

- Three Colored Filters

To perform the experiment, use the setup depicted at Fig. 2. The single ray of light should pass through the centre of the Ray Table.

a)      Slowly rotate the Ray Table to increase the angle of incidence of the light ray.

b)      Examine the refracted ray on the Viewing Screen.

c)      Notice the colour separation at large angles of refraction and record the angle of incidence at which the color separation is a maximum. Write the order the colors appear in the refracted beam starting with the color that experienced the smallest deflection.

d)      Use your observations to confirm Newton's theory of light colours.

 

To continue the experiment, arrange the Cylindrical Lens so that the three central light rays (the red, the green and the blue) intersect at precisely the same point on the Ray Table (see Fig. 3).

 

 


What color of light results when red, green, and blue light are mixed? How does this support Newton's theory?

To study the formation of colors of objects, set up equipment as in Fig. 4.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a)      Observe the light rays that are transmitted through the Green Filter. What color are the transmitted rays?

b)      Observe the light rays reflected from the Green Filter. What color are the reflected rays?

c)      Combine the red filter and the green filter so the light passes first through the Green Filter and then through the Red Filter. Look into the Green Filter. What color rays are reflected from the front surface of the Green Filter? Which rays are reflected from the front surface of the Red Filter?

d)      Place the Blue Filter over the Light Source aperture so the incident rays are blue. Let these rays pass through the Green Filter only. What colors are the reflected rays now?

e)      Based on your observations, conclude on what makes the Green Filter appear green.

f)        What makes a green leaf appear green?

 

 

 

This Student Guide was created by Natalia Krasnopolskaia in October 2014.