PASCO OS-8459 User Manual

Instruction Manual with

Experiment Guide and

Teachers’ Notes

012-09655A

Beginning Optics System

OS-8459

Optics Bench

Basic Optics System Table of Contents

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

About the Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

About the Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Experiment 1: Color Addition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Experiment 2: Prism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Experiment 3: Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Experiment 4: Snell’s Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Experiment 5: Total Internal Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Experiment 6: Convex and Concave Lenses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Experiment 7: Hollow Lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Experiment 8: Lensmaker’s Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Experiment 9: Apparent Depth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Experiment 10: Focal Length and Magnification of a Thin Lens . . . . . . . . . . . . . . . . . . 27

Experiment 11: Telescope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Experiment 12: Microscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Experiment 13: Shadows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Telescope and Microscope Test Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Teacher’s Guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Beginning Optics System

OS-8459

Optics Bench

Included Equipment Part Number

1. 1.2 m Optics Bench OS-8508

2. Viewing Screen OS-8467

3. +100 mm Mounted Lens 003-07204

4. +200 mm Mounted Lens 003-07205

5. Light Source OS-8470

6. Ray Optics Kit with: OS-8516A a. Storage Box/Water Tank 740-177 b. Mirror 636-05100 c. Hollow Lens OS-8511 d. Convex Lens 636-05501 e. Concave Lens 636-05502 f. Acrylic Rhombus 636-05611

Introduction

The PASCO Beginning Optics System contains the optics components you will need for a variety of experiments and demonstrations. This manual includes student instructions and teacher’s notes for 13 typical experiments.

For an even greater variety, you can expand the system with any of the Beginning Optics kits and components available from PASCO, including lasers, polarizers, diffraction slits, and light sensors. See the PASCO Physics catalog or visit www.pasco.com for details.

Beginning Optics System About the Equipment

About the Equipment

For detailed information on the Light Source and Ray Optics Kit, see the instruction sheets included with those components.

Optics Bench Basic Optics components, such as mounted lenses and the adjustable lens holder, snap into the wide centra l channel of the optics bench. Place the base of the component on the bench and push down firmly to snap it in place. To move it, squeeze the tab on base and slide it along the bench.

Components that include a square bolt and a thumb screw are designed to be fasted to the T -slots on the sides and center of the bench. Slide the bolt into the T -slot, insert the thumb screw through the component’s mounting hold, thread the screw into the bolt and tighten it down.

Use the metric scale on the bench to measure the positions of components.

metric scale for measuring component positions

Light Source The included light source can be used on a tabletop or mounted on the bench. It functions as a bright point source, an illuminated crossed-arrow object, a primary-color source, and a ray box with up to five parallel rays.

Mounted Lenses The Beginning Optics System includes two lenses mounted in holders. Use them on the optics bench with the light source, viewing screen, and other Basic Optics components.

Viewing Screen Mount the screen on the bench to view real images formed by lenses.

Ray Optics Kit The ray optics kit is a set of optics components designed for use with the light source in ray-box mode. To make the rays easy to see and trace, use the ray optics components on a white sheet of paper on a flat table top. The transparent storage box doubles as a water tank for studying lenses under water.

About the Experiments

The experiment instructions on the following pages are arranged and categorized according to which components of the Beginning Optics System they use. See the table at the top of each experiment for a detailed list of required equipment. T eachers’ notes, including typical data and answers to questions, can be found starting on page 43.

T-slots

The experiments that call for the light source work best in a dimly lit room.

Ray Optics Kit Experiments These experiments use the Ray Optics Kit, the Light Source (in ray-box mode), and may require blank white paper, a ruler, protractor, and drawing compass.

1. Color Addition (p age 7): Explore the results of mixing colored ligh t and illumi-

nating colored ink with colored light.

2. Prism (page 9): Show how a prism separates white light into its component col-

ors and show that different colors are refracted at different angles through a prism.

3. Reflection (page 11): Show how rays are reflected from plane, concave, and con-

vex mirrors.

Model No. OS-8459 About the Experiments

4. Snell’s Law (page 13): Determine the index of refraction of acrylic by measuring

angles of incidence and refraction of a ray passing through the rhombus.

5. Total Internal Reflection (page 15): Determine the critical angle at which total

internal reflection occurs in the rhombus.

6. Convex and Concave Lenses (page 17): Use ray tracing to determine the focal

lengths of lenses.

7. Hollow Lens (page 19): Use the hollow lens and water to expl ore how the prop-

erties of a lens are related to its shape, its index of refraction, and the index of refraction of the surrounding medium.

8. Lensmaker’s Equation (page 21): Determine the focal length of a concave lens

by measuring its radius of curvature.

9. Apparent Depth (page 23): Measu re the apparent dep th of the rhombu s and

determine its index of refraction by comparing the apparent depth to the actual thickness.

Optics Bench Experiments These experiments use the Optics Bench, Mounted Lenses, and Viewing Screen. Experiments 10 and 13 also use the Light Source.

10. Focal Length and Magnification of a Thin Lens (page 27): Determine the

focal length of a converging lens by forming an image on the viewing screen.

11. Telescope (page 31): Construct a telescope and determine its magnification.

12. Microscope (page 35): Construct a microscope and determine its magnification.

13. Shadows (page 39): Show the um bra and the penum bra of a shadow.

Beginning Optics System About the Experiments

Model No. OS-8459 Experiment 1: Color Addition

Experiment 1: Color Addition

Required Equipment from Beginning Optics System

Light Source Convex Lens from Ray Optics Kit

Other Required Equipment

Red, blue, and black pens Blank white paper

Purpose

In Part 1 of this experiment, you will discover the results of

Light source

mixing red, green, and blue light in different combinations. In Part 2, you will compare the appearance of red, blue, and black ink illuminated by red and blue light.

Part 1: Addition of Colored Light Procedure

1. Turn the wheel on the light source to select the red,

green, and blue color bars. Fold a blank, white sheet of paper, as shown in Figure 1.1. Lay the paper on a flat surface and put the light source on it so that the colored rays are projected along the horizontal part of the paper and onto the vertical part.

2. Place the convex lens near the ray box so it focuses the rays and causes them to

cross at the vertical part of the paper.

Note: The lens has one flat edge. Place the flat edge on the paper so the lens stands stably without rocking.

3. What is the resulting color where the three

colors come together? Record your observation in Table 1.1.

4. Now block th e green ray with a pencil.

What color results from adding red and blue light? Record the result in Table 1.1.

red + blue + green red + blue red + green

Table 1.1: Results of Colored Light Addition

Colors Added Resulting Color

Convex lens

Folded paper

Red, green, and blue rays

Combined colors

Figure 1.1: Color addition

5. Block each color in succession to see the

green + blue

addition of the other two colors and complete Table 1.1.

Questions

1. Is mixing colored light the same as mixing colored paint? Explain.

2. White lig ht is said to be the mixture of all colors. In this experiment, did mixing

red, green, and blue light result in white? Explain.

Beginning Optics System Experiment 1: Color Addition

Part 2: Observing Colored Ink Under Colored Light Procedure

1. While you lo ok away, have your partner draw two lines—one red and one

black—on a sheet of white paper. One of the lines should be labeled A, and the other B, but you should not know which is which.

Before you look at the paper, have your partner turn off the room lights and cover the red and green bars so the paper is illuminated only with blue light.

Now look. What colors do the two lines appear to be? Do they appear to be different colors? Record your observations in Table 1.2.

Finally, observe the lines under white light and record their actual colors in Table

1.2.

2. Repeat step 1, but this time have your partner draw lines using blue and black ink

(labeled C and D), and observe them under red light.

3. For Trial 2, switch roles and repeat steps 1 and 2 with the your partner observing

lines that you have drawn. Record the results in Table 1.2. (For this trial, you may try to trick your partner by drawing both lines the same color—both red or both black, for instance.)

Table 1.2: Colored Ink Observed Under Colored Light

Trial 1: Name of observer: ______________________________________

Color of Light Line Apparent Color of Ink Do they look different? Actual Color of Ink

Blue Light

Red Light

Trial 2: Name of observer: ______________________________________

Color of Light Line Apparent Color of Ink Do they look different? Actual Color of Ink

Blue Light

Red Light

A B C D

4. Look a red line and black lines under red light. Which line is easier to see?

_________________________

Questions

1. What makes red ink appear red? When red ink is illumined by blue light, is most

of the light absorbed or reflected?

2. When illum ined with red light, why is red ink on white paper more difficult to

see than black ink?

Model No. OS-8459 Experiment 2: Prism

Experiment 2: Prism

Required Equipment from Beginning Optics System

Light Source Rhombus from Ray Optics Kit Blank white paper

Purpose

Incident ray

The purpose of this experiment is to show how a prism separates white light into its component colors and to show that different colors are refracted at different angles through a prism.

Theory

When a monochromatic light ray crosses from one medium (such as air) to another (such as acrylic), it is refracted. According to Snell’s Law,

sin θ1 = n2sin θ

Figure 2.1: Refraction of Light

the angle of refraction (θ2) depends on the angle of incidence (θ1) and the indices of refraction of both media (n

and n2), as shown in Figure 2.1. Because the index of

refraction for light varies with the frequency of the light, white light that enters the material (at an angle other than 0°) will separate into its component colors as each frequency is bent a different amount.

The rhombus is made of acrylic which has an index of refraction of 1.497 for light of wavelength 486 nm in a vacuum (blue light), 1.491 for wavelength 589 nm (yellow), and 1.489 for wavelength 651 nm (red). In general for visible light, index of refraction increases with increasing frequency.

Normal to surface

Surface

Refracted ray

> n

)

Procedure

1. Place the light source in ray-box mode on a sheet of blank white paper. Turn the

wheel to select a single white ray.

Color

spectrum

Single white ray

Normal to surface

Figure 2.2

2. Position the rhombus as shown in Figure 2.2. The acute-angled end of the rhom-

bus is used as a prism in this experiment. Keep the ray near the point of the rhombus for maximum transmission of the light.

Beginning Optics System Experiment 2: Prism

3. Rotate the rhombus until the angle (θ) of the emerging ray is as large as possible

and the ray separates into colors.

(a) What colors do you see? In what order are they?

(b) Which color is refracted at the largest angle?

dependence of the index of refraction for acrylic, which color is predicted to refract at the largest angle?

4. Without repositioning the light source, turn the wheel to select the three primary

color rays. The colored rays should enter rhombus at the same angle that the white ray did. Do the colored rays emerge from the rhombus parallel to each other? Why or why not?

Model No. OS-8459 Experiment 3: Reflection

Experiment 3: Reflection

Required Equipment from Beginning Optics System

Light Source Mirror from Ray Optics Kit

Other Required Equipment

Drawing compass Protractor Metric ruler White paper

Purpose

In this experiment, you will study how rays are reflected from different types of mirrors. You will measure the focal length and determine the radius of curvature of a concave mirror and a convex mirror.

Part 1: Plane Mirror Procedure

1. Place the light source in ray-box mode on a blank sheet of

white paper. Turn the wheel to select a single ray.

2. Place the mirror on the paper. Position the plane (flat) surface

of the mirror in the path of the incident ray at an angle that allows you to clearly see the incident and reflected rays.

3. On the paper, trace and label the surface of the plane mirror

and the incident and reflected rays. Indicate the incoming and the outgoing rays with arrows in the appropriate directions.

4. Remove the light source and mirror from the paper. On the

paper, draw the normal to the surface (as in Figure 3.1).

5. Measure the angle of incidence and the angle of reflection. Measure these angles

from the normal. Record the angles in the first row Table 3.1.

6. Repeat steps 1–5 with a different angle of incidence. Repeat the procedure again

to complete Table 3.1 with three different angles of incidence.

Table 3.1: Plane Mirror Results

Normal to

surface

Incident ray

Reflected ray

Figure 3.1

Angle of Incidence Angle of Reflection

7. Turn the wheel on the light source to select the three primary color rays. Shine

the colored rays at an angle to the plane mirror. Mark the position of the surface of the plane mirror and trace the incident and reflected rays. Indicate the colors of

Beginning Optics System Experiment 3: Reflection

the incoming and the outgoing rays and mark them with arrows in the appropriate directions.

Questions

1. What is the relationship between the angles of incidence and reflection?

2. Are the three colored rays reversed left-to-right by the plane mirror?

Part 2: Cylindrical Mirrors Theory

mirror

A concave cylindrical mirror focuses incoming parallel rays at its focal point. The focal length ( f) is the distance from the focal point to the center of the mirror surface. The radius of curvature (R) of the mirror is twice the focal length. See Figure 3.2.

focal point

Procedure

1. Turn the wheel on the light source to select five parallel rays. Shine

the rays straight into the concave mirror so that the light is reflected back toward the ray box (see Figure 3.3). Trace the surface of the mirror and the incident and reflected rays. Indicate the incoming and the outgoing rays with arrows in the appropriate directions. (You can now remove the light source and mirror from the paper.)

2. The place where the five reflected rays cross each other is the focal

point of the mirror. Mark the focal point.

Incident rays

3. Measure the focal length from the center of the concave mirror sur-

face (where the middle ray hit the mirror) to the focal point. Record the result in Table 3.2.

4. Use a compass to draw a circle that matches the curvature of the

mirror (you will have to make several tries with the compass set to different widths before you find the right one). Measure the radius of curvature and record it in Table 3.2.

5. Repeat steps 1–4 for the convex mirror. Note that in step 3, the reflected rays will

diverge, and they will not cross. Use a ruler to extend the reflected rays back behind the mirror’s surface. The focal point is where these extended rays cross.

Table 3.2: Cylindrical Mirror Results

Figure 3.2

Figure 3.3

Concave Mirror Convex Mirror

Focal Length Radius of Curvature

(determined using compass)

Questions

1. What is the relationship between the focal length of a cylindrical mirror and its

radius of curvature? Do your results confirm your answer?

2. What is the radius of curvature of a plane mirror?

Model No. OS-8459 Experiment 4: Snell’s Law

Experiment 4: Snell’s Law

Required Equipment from Beginning Optics System

Light Source Rhombus from Ray Optics Kit

Other Required Equipment

Protractor White paper

Purpose

The purpose of this experiment is to determine the index of refraction of the acrylic rhombus. For rays entering the rhombus, you will measure the angles of incidence and refraction and use Snell’s Law to calculate the index of refraction.

Theory

For light crossing the boundary between two transparent materials, Snell’s Law states

sin θ1 = n2sin θ

where θ1 is the angle of incidence, θ2 is the angle of refraction, and n

and n2 are the respective indices of

refraction of the materials (see Figure 4.1).

Procedure

1. Place the light source in ray-box mode on a sheet of

white paper. Turn the wheel to select a single ray.

2. Place the rhombus on the paper and position it so

the ray passes through the parallel sides as shown in Figure 4.2.

Incident ray

Figure 4.1

Normal to surface

Surface

Refracted ray

> n

)

3. Mark the position of the parallel surfaces of the

Figure 4.2

rhombus and trace the incident and transmitted rays. Indicate the incoming and the outgoing rays with arrows in the appropriate directions. Carefully mark where the rays enter and leave the rhombus.

4. Remove the rhombus and draw a line on the paper connecting the points where

the rays entered and left the rhombus. This line represents the ray inside the rhombus.

5. Choose either the point where the ray enters the rhombus or the point where the

ray leaves the rhombus. At this point, draw the normal to the surface.

6. Measure the angle of incidence (θ

) and the angle of refraction with a protractor.

Both of these angles should be measured from the normal. Record the angles in the first row of Table 4.1.

Beginning Optics System Experiment 4: Snell’s Law

7. On a new sheet of paper, repeat steps 2–6 with a different angle of incidence.

Repeat these steps again with a third angle of incidence. The first two columns of Table 4.1 should now be filled.

Table 4.1: Data and Results

Angle of Incidence Angle of Refraction Calculated index of refraction of

acrylic

Average:

Analysis

1. For each row of Table 4.1, use Snell’s Law to calculate the index of refraction,

assuming the index of refraction of air is 1.0.

2. Average the three values of the index of refraction. Compare the average to the

accepted value (n = 1.5) by calculating the percent difference.

Question

What is the angle of the ray that leaves the rhombus relative to the ray that enters it?

Model No. OS-8459 Experiment 5: Total Internal Reflection

Experiment 5: Total Internal Reflection

Required Equipment from Beginning Optics System

Light Source Rhombus from Ray Optics Kit

Other Required Equipment

Protractor White paper

Purpose

In this experiment, you will determine the critical angle at which total internal reflection occurs in the acrylic rhombus and confirm your result using Snell’s Law.

Theory

For light crossing the boundary between two transparent materials, Snell’s Law states

sin θ1 = n2sin θ

where θ1 is the angle of incidence, θ2 is the angle of refraction, and n

and n2 are the respective indices of

refraction of the materials (see Figure 5.1).

In this experiment, you will study a ray as it passes out of the rhombus, from acrylic (n =1.5) to air (n

If the incident angle (θ angle (θ

), there is no refracted ray and total internal

reflection occurs. If θ

) is 90°, as in Figure 5.2.

ray (θ

) is greater than the critical

= θc, the angle of the refracted

In this case, Snell’s Law states:

n sin θc = 1 sin 90°

Solving for the sine of critical angle gives:

sin θ

-- -=

air

=1).

Incident ray

= 1

air

Figure 5.1

90°

Reflected ray

Surface

Refracted ray

> n

Reflected ray

Refracted ray

)

Figure 5.2

Beginning Optics System Experiment 5: Total Internal Reflection

point

Re po

Procedure

1. Place the light source in ray-box mode on a sheet of white paper. Turn the

wheel to select a single ray.

2. Position the rhombus as shown in Figure 5.3, with the ray entering the

rhombus at least 2 cm from the tip.

3. Rotate

the rhombus until the emerging ray just barely disappears. Just as

it disappears, the ray separates into colors. The rhombus is correctly positioned if the red has just disappeared.

4. Mark the surfaces of the rhombus. Mark exactly the point on the surface

where the ray is internally reflected. Also mark the entrance point of the incident ray and the exit point of the reflected ray.

5. Remove the rhombus and draw the rays that are incident upon and

reflected from the inside surface of the rhombus. See Figure 5.4. Measure the angle between these rays using a protractor. (Extend these rays to make the protractor easier to use.) Note that this angle is twice the critical angle because the angle of incidence equals the angle of reflection. Record the critical angle here:

= _______ (experimental)

Reflected

ray

Incident

ray

Exit point

Entrance point

Figure 5.3

Refracted Ray

Reflection point

6. Calculate the critical angle using Snell’s Law and the given index of

refraction for Acrylic (n = 1.5). Record the theoretical value here:

= _______ (theoretical)

7. Calculate the percent difference between the measured and theoretical values:

% difference = _______

Questions

1. How does the brightness of the internally reflected ray change when the incident

angle changes from less than θ

2. Is the critical angle greater for red light or violet light? What does this tell you

about the index of refraction?

to greater than θc?

Figure 5.4

+ 35 hidden pages