Pasco Scientific OS-8537 User manual

012-06575A
3/98
©1998 PASCO scientific $10.00
EDUCATIONAL SPECTROPHOTOMETER
ACCESSORY KIT AND EDUCATIONAL
SPECTROPHOTOMETER SYSTEM
Instruction Manual and
Experiment Guide for the
PASCO scientific Model
OS-8537 and OS-8539
better
teach science
ways to
Phone [phone] • FAX [phone] • web: www.pasco.com
10101 Foothills Blvd. • Roseville, CA 95747-7100 USA
®
POLARIZER MOUNTPOLARIZER MOUNT
10
1
100
GAIN
LIGHT
SENSOR
CI-6604A
10
1
100
GAIN
LIGHT
SENSOR
CI-6604A

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012-06575A Educational Spectrophotometer
Table of Contents
Section Page
Copyright, Warranty, and Equipment Return .....................................................ii
Quick Start........................................................................................................1
Introduction ......................................................................................................3
Description .......................................................................................................4
Set Up
Mounting the Rotary Motion Sensor ...........................................................5
Mounting the Degree Plate and Light Sensor Arm .......................................6
More Information About the Degree Plate ...................................................6
Mounting the Aperture Bracket Light Sensor Mount and Light Sensor ........7
Mounting the Grating Mount.......................................................................8
Mounting the Spectrophotometer Base on the Optics Bench ........................8
Rod Stand Mounting Clamps ......................................................................8
Mounting the Collimating Slits and Lens.....................................................9
Positioning the Collimating Slits and Lens...................................................9
Mounting the Grating.................................................................................10
Mounting and Positioning the Focusing Lens .............................................10
Procedures
Turning the Degree Plate............................................................................11
Masking the Light Source or the Spectrophotometer...................................11
Using the ScienceWorkshop Program .........................................................11
General Information About the Light Sensor ..............................................12
General Information About Slit Widths ......................................................12
Scanning a Spectrum..................................................................................12
Calibrating the Grating ...............................................................................13
Other Information ......................................................................................13
Activities
Activity 1: Emission Spectrum ...................................................................15
Activity 2: Absorption Spectrum ................................................................19
Teacher’s Guide...............................................................................................23
Technical Support ......................................................................... Inside Back Cover

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Educational Spectrophotometer 012-06575A
Equipment Return
Should this product have to be returned to PASCO
scientific, for whatever reason, notify PASCO scientific
by letter or phone BEFORE returning the product. Upon
notification, the return authorization and shipping instruc-
tions will be promptly issued.
When returning equipment for repair, the units must be
packed properly. Carriers will not accept responsibility
for damage caused by improper packing. To be certain
the unit will not be damaged in shipment, observe the
following rules:
➀The carton must be strong enough for the item
shipped.
➁Make certain there is at least two inches of packing
material between any point on the apparatus and the
inside walls of the carton.
➂Make certain that the packing material can not shift in
the box, or become compressed, thus letting the instru-
ment come in contact with the edge of the box.
Address: PASCO scientific
10101 Foothills Blvd.
Roseville, CA 95747-7100
Phone: [phone]
FAX: [phone]
Copyright Notice
The PASCO scientific manual for the Model OS-8537
Educational Spectrophotometer Accessory Kit and OS-
8539 Educational Spectrophotometer System is copy-
righted and all rights reserved. However, permission is
granted to non-profit educational institutions for repro-
duction of any part of this manual providing the reproduc-
tions are used only for their laboratories and are not sold
for profit. Reproduction under any other circumstances,
without the written consent of PASCO scientific, is
prohibited.
Limited Warranty
PASCO scientific warrants this product to be free from
defects in materials and workmanship for a period of one
year from the date of shipment to the customer. PASCO
will repair or replace, at its option, any part of the product
which is deemed to be defective in material or workman-
ship. This warranty does not cover damage to the product
caused by abuse or improper use. Determination of
whether a product failure is the result of a manufacturing
defect or improper use by the customer shall be made
solely by PASCO scientific. Responsibility for the return
of equipment for warranty repair belongs to the customer.
Equipment must be properly packed to prevent damage
and shipped postage or freight prepaid. (Damage caused
by improper packing of the equipment for return ship-
ment will not be covered by the warranty.) Shipping costs
for returning the equipment, after repair, will be paid by
PASCO scientific.
Copyright, Warranty and Equipment Return
Please—Feel free to duplicate this manual
subject to the copyright restrictions below.
Credits
Edited by: Dave Griffith
➤NOTE:
NO EQUIPMENT WILL BE ACCEPTED FOR
RETURN WITHOUT AN AUTHORIZATION.

1
012-06575A Quick Start Educational Spectrophotometer
Quick Start
thumbscrew
three-step pulley
Rotary Motion Sensor
rod clamp
Quick Start 1: Prepare Rotary Motion Sensor
Remove the
Pinion
Rotate the
hinge.
Remove the
thumbscrews.
Spectrophotometer Base
Quick Start 2: Prepare the Hinge
Rotary Motion
Sensor
Use the thumbscrews to
attach the sensor.
Put the Pinion
on the shaft.
hinge
Spectrophotometer Base
Quick Start 3: Attach the Sensor and Pinion
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HIGHSENSITIVITY
LIGHTSENSOR
CI-6604
lock washer
Degree
Plate
Light
Sensor
Arm
Grating
Mount
Light Sensor Mount with
Aperture Disk and Screen
Light
Sensor
threaded
post
wing nut
Focusing
Lens
Quick Start 4: Degree Plate & Light Sensor Arm, Grating Mount,
Focusing Lens, Light Sensor Mount, and Light Sensor
The following pages give an overview of the Spectrophotometer equipment setup.
Step One: Prepare the Rotary Motion Sensor by
removing the thumbscrew, three-step pulley, and
rod clamp.
Step Two: Prepare the Spectrophotometer Base by
removng the two small thumbscrews and Pinion
and by rotating the hinge away from the Base.
Step Three: Attach the Rotary Motion Sensor to
the Base hinge with the two small thumbscrews and
attach the Pinion to the Rotary Motion Sensor shaft.
Step Four: Put the Degree Plate/Light Sensor
Arm on the Base. Attach the Grating Mount,
Light Sensor Mount, and Light Sensor. Position
the Focusing Lens.

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Educational Spectrophotometer Quick Start 012-06575A
Base
Optics Bench
thumbscrew
square nut
T-slot
hinge
Quick Start 5: Put Base onto Optics Bench
Step Five: Put the Spectrophotometer Base onto one
end of the Optics Bench.
Step Six: Mount the Collimating Slits and Collimating
Lens onto the Optics Bench. Set up a light source.
Adjust the Collimating Slits and Collimating Lens to
collimate the light beam.
GAIN
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1
Degree
Plate
light
source
Collimating
Slits
Collimating
Lens
light ray
path
Quick Start 6: Setup for Collimation
Step Seven: Attach the Grating to the mount so the
glass side of the Grating faces the light source.
CAUTION: Avoid touching the Grating surface.
Step Eight: Set up the experiment in the
ScienceWorkshop program.
1. Select the Light Sensor for Analog Channel A.
2. Select the Rotary Motion Sensor for Digital
Channels 1 and 2.
3. Set the Rotary Motion Sensor to high resolution
(1440 Divisions/Rotation).
4. Create a calculation for “Actual Angular Posi-
tion” based on the Angular Position data from the
Rotary Motion Sensor and the ratio of the radius
of the Degree Plate to the radius of the small post
on the Pinion (typically, a 60 to 1 ratio).
5. Select a Graph display. Set the vertical axis to
Light Intensity and the horizontal axis to your
calculation of “Actual Angular Position”.
6. Set the sampling rate to 20 Hz (20 measurements
per second).
Step Nine: Scan the Spectrum
1. Mask or hood the light source if necessary.
2. Move the Light Sensor Arm so the Light Sensor
is beyond the edge of the first order spectral
pattern.
3. Start recording data. Slowly and continuously
scan the spectrum. Scan the first order spectrum
on one side of the central ray, through the central
ray, and through the first order spectrum on the
other side.
Step Ten: Analyze Your Data
glass side faces light source
Quick Start 7: Attach the Grating
Grating
GAIN
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1
Scan slowly and
continuously in one
direction.
central ray
(“zeroth order”)
first order spectral lines
first order spectral lines
Grating
Quick Start 9: Scan the Spectrum

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012-06575A Educational Spectrophotometer
Introduction
About This Manual
This manual describes the PASCO OS-8537 Educational Spectrophotometer Accessory Kit and the PASCO OS-8539
Educational Spectrophotometer System. The OS-8537 Accessory Kit is designed to be mounted on the Optics Bench of
the OS-8515 Basic Optics System.
Components of the Kit
The OS-8537 Educational Spectrophotometer Accessory Kit (see Figure 1a) includes the following items:
Spectrophotometer Base Degree Plate with Light Sensor Arm
Grating Mount Grating (~600 lines per mm)
Focusing Lens Collimating Lens
Collimating Slits Cuvettes (2)
Rod Stand Mounting Brackets (2)
(*The pinion shown in Figure 1a can be mounted on a post on the Spectrophotometer Base when not in use.)
Recommended Equipment for use with the Spectrophotometer Accessory Kit:
Basic Optics System (OS-8515) High Sensitivity Light Sensor (CI-6604)
Aperture Bracket (OS-8534) Rotary Motion Sensor (CI-6538)
Grating Mount
Grating
Collimating Slits Collimating Lens Pinion* Cuvettes (2)
Spectrophotometer
Base
Degree Plate
Light Sensor Arm
Focusing Lens
Rod Stand Mounting
Clamps (2)
Figure 1a: Educational Spectrophotometer Accessory Kit

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Educational Spectrophotometer 012-06575A
Light Source
Collimating Slit
Collimating Lens Diffraction Grating
Focusing Lens
spectral line
θ
Figure 2: Grating Spectrometer
Components of the System
The OS-8539 Educational Spectrophotometer System includes the items in the Spectrophotometer Accessory Kit
plus the following:
Optics Bench (60 cm) Rotary Motion Sensor (CI-6538)
High Sensitivity Light Sensor (CI-6604) Aperture Bracket (OS-8534)
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LIGHT
SENSOR
CI-6604A
POLARIZERMOUNT
High Sensitivity Light SensorDIN-to-DIN cable Optics Bench (60 cm)
Rotary Motion Sensor
Aperture Bracket Holder
Aperture Bracket
Figure 1b: Additional Components of the Spectrophotometer System
Description
The Spectrophotometer allows you to view and measure the spectral pattern (spectrum) produced by a light source.
The Collimating Slits and Collimating Lens produce a narrow beam of parallel light rays. The Grating disperses
the beam of light into a spectrum with different colors at different angles but with all of the light of a given color
in a parallel beam. The Focusing Lens focuses these parallel beams of color into spectral lines (see Fig. 2). The
narrow slit on the Aperture Disk (part of the Aperture Bracket) allows light of a single color to enter the High Sen-
sitivity Light Sensor. The High Sensitivity Light Sensor (included with the Spectrophotometer System) measures
the intensity of the light while the Rotary Motion Sensor (included with the Spectrophotometer System) measures
the angle to which the light is diffracted by the
Grating.
You can find the wavelength of each color of
light using the measured angle and the Grating
spacing “d”.
mλ= d sin θ, m = 0, 1, 2…
where d is the distance between the rulings on
the Grating, m is the order of the particular
principal maximum, θis the angle of the
diffracted light, and λis the wavelength.
Recommended Equipment for use with both the Kit and the System:
Light Source (such as OS-9286 Mercury Light) Large Rod Stand (ME-8735) (2)
Rod, 45 cm (ME-8736) (2)

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012-06575A Educational Spectrophotometer
This part of the manual describes how to set up the
Spectrophotometer System (see Fig. 3).
Mounting the Rotary Motion Sensor
This describes how to mount the Rotary Motion
Sensor to the hinge on the side of the Spectrophotom-
eter Base.
The top of the Spectrophotometer Base has a short
threaded post for centering the circular Degree Plate
and for holding the Grating Mount. It also has a
magnetic pad for holding the Degree Plate, and a
triangular shaped index marker. One side of the base
has a post upon which the Pinion can be stored when it
is not in use. The other side has a spring-loaded hinge and
two small thumbscrews for mounting the Rotary Motion
Sensor (included in the Spectrophotometer System). On
both sides of the base are thumbscrews and square nuts used
for mounting the Spectrophotometer Base on the Optics
Bench (see Fig. 4).
The Rotary Motion Sensor has a three step pulley attached
to its shaft with a small thumbscrew. The sensor also has a
rod clamp attached at end end.
First, remove the small thumbscrew and three step pulley
from the Rotary Motion Sensor shaft. Then, remove the rod
clamp from the Rotary Motion Sensor (see Fig. 5).
hinge
Spectrophotometer Base
magnetic pad Pinion
index
small
thumbscrews
large
thumbscrew
Figure 4: Spectrophotometer Base (Top View)
threaded post
thumbscrew
three-step pulley
Rotary Motion Sensor
rod clamp
Figure 5: Prepare Rotary Motion Sensor
Set Up
The Grating disperses the beam of
light into a first order spectrum
and higher order spectra. The
higher order spectra are broader
and less bright than the first order
spectra, and may overlap.
The Grating is blazed, so one side
of the spectrum is much brighter
than the other.
Light Source
Collimating Lens
Optics Bench
Degree Plate
Grating Mount
Diffraction Grating
Light Sensor Arm
Focusing Lens
Aperture Disk
High Sensitivity Light Sensor
Rotary Motion Sensor Pinion
Figure 3: Spectrophotometer System (Top View)
Collimating Slit

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Educational Spectrophotometer 012-06575A
Remove the
Pinion
Rotate the
hinge.
Remove the
thumbscrews.
Spectrophotometer Base
Figure 6: Prepare the Hinge
Rotary Motion
Sensor
Use the thumbscrews to
attach the sensor.
Put the Pinion
on the shaft.
hinge
Spectrophotometer Base
Figure 7: Attach the Sensor and Pinion
Remove the two small thumbscrews from the threaded
storage holes on the side of the Spectrophotometer Base
and set them aside for the moment. Remove the Pinion
from the storage post on the opposite side of the Spectro-
photometer Base and set the Pinion aside for a moment (see
Fig. 6).
Rotate the hinge away from the side of the base until the
hinge is almost perpendicular to the base. Use the two
small thumbscrews to fasten the Rotary Motion Sensor to
the lower set of holes on the inside of the hinge.
Place the Pinion all the way onto the Rotary Motion Sensor
shaft and tighten the Pinion on the shaft by turning the
small thumbscrew on the side of the Pinion (see Fig. 7).
Connect the Rotary Motion Sensor plugs into the
ScienceWorkshop interface.
Mounting the Degree Plate and Light Sensor Arm
The Degree Plate and Light Sensor Arm are shipped as a
unit. The Light Sensor Arm is attached to the circular
Degree Plate with two small thumbscrews. The hole in
the center of the Degree Plate fits over the short threaded
post on the top of the Spectrophotometer Base.
Hold the Rotary Motion Sensor slightly away from the
base so the small diameter post on top of the Pinion is not
in the way of the edge of the Degree Plate. Position the
hole in the plate over the short threaded post on the top of
the base. Place the Degree Plate onto the Spectrophotom-
eter Base. Let the small diameter post on the top of the
Pinion rest against the edge of the Degree Plate (see Fig.
8).
More Information About the Degree Plate
The ratio between the radius of the Degree Plate and
the radius of the small post on the top of the Pinion is
designed to be 60 to 1. In other words, the Pinion
rotates 60 times for one rotation of the Degree Plate.
This assumed ratio of 60 to 1 is included in a calcula-
tion for the actual angular displacement of the Degree
Plate as it turns during the measurement of a spectrum
(see “Using the ScienceWorkshop Program” in the
Procedure section).
Using the exact ratio of the Degree Plate to the small
Pinion post can slightly improve the accuracy of
measurement. To determine the exact ratio of the
Degree Plate to the small Pinion post, do the following
to calibrate the Degree Plate:
Degree Plate
Light Sensor
Arm
Rotary Motion
Sensor
Pinion
Let the post on top of the
Pinion rest against the
edge of the Degree Plate.
Figure 8: Degree Plate onto Base

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012-06575A Educational Spectrophotometer
1. Remove the Light Sensor Arm from the Degree Plate by unscrewing the two small thumbscrews. (You can
store the thumbscrews in the empty threaded holes on the Light Sensor Arm.) Turn the Degree Plate so the zero
degree mark is exactly aligned with the index mark on the arm that extends from the Spectrophotometer Base.
2. Start the ScienceWorkshop program. (See the ScienceWorkshop User’s Guide for more information.)
3. In the ScienceWorkshop program, select the Rotary Motion Sensor to be connected to Digital Channels 1 and 2.
Set the resolution of the Rotary Motion Sensor to
1440 Divisions/Rotation.
4. In the program, use the built-in Calculator to create
a calculation. Base the calculation on the “Angular
Position” measurement from the Rotary Motion
Sensor. In the calculation, divide “Angular Posi-
tion” by 2π, where πis approximately 3.1416…
Label your calculation “Ratio of Radii” (Fig. 9).
5. In the program, select a Graph display and set it to
show the calculation “Ratio of Radii” on its
vertical axis.
6. Start recording data. Turn the Degree Plate in one
direction slowly and continuously for exactly one
complete rotation. Stop recording data.
7. In the Graph display, use the built-in
Statistics tools to find the maximum
value of the “Ratio of Radii” (i.e., the
maximum of y - see Fig. 10). This value
is the exact ratio of the Degree Plate
radius to the small Pinion post radius.
(Note: This value should be close to 60.)
Record the actual ratio.
Ratio of Radii = _______
8. Replace the Light Sensor Arm on the Degree Plate and fasten it to the plate with the two small thumbscrews.
Mounting the Aperture Bracket Light Sensor Mount and Light Sensor
The Aperture Bracket has two main parts: the Light Sensor Mount
and the Holder. (The Holder and thumbscrew are not used and can
be put aside.) An Aperture Disk and Aperture Screen are attached to
the front of the Light Sensor Mount.
The Light Sensor Mount has two holes: one hole in the center of the
mount and a second hole at the rear of the mount. The end of the
Light Sensor Arm has three holes: two holes along the centerline of
the arm and one hole to the side of the centerline. Line up the center
hole of the Light Sensor Mount with the centerline hole in the Light
Sensor Arm that is closest to the Degree Plate.
Line up the High Sensitivity Light Sensor so the threaded hole in its
base is above the center hole of the Light Sensor Mount. Use the
threaded post (included with the Aperture Bracket) to fasten the
High Sensitivity Light Sensor and Light Sensor Mount to the Light
Sensor Arm (Fig. 11).
Figure 10: Sample Degree Plate Calibration Data
NOTE: The Graph display
in your version of
ScienceWorkshop may
differ in appearance. Refer
to your User’s Guide.
maximum y value = Ratio of Radii
HIGH SENSITIVITY
LIGHT SENSOR
CI-6604
High Sensitivity
Light Sensor
Aperture Bracket
Light Sensor Mount
Light Sensor Arm
threaded post
Figure 11: Sensor and Aperture
Bracket onto Light Sensor Arm
Expression for the “Angular
Position” data from the Rotary
Motion Sensor 2π
label for the
calculation
Figure 9: Calculation for Ratio of Radii
NOTE: The Experiment
Calculator for your version
of ScienceWorkshop may
differ in appearance. Refer
to your User’s Guide.

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Educational Spectrophotometer 012-06575A
Rotate the Aperture Disk on the front of the Light Sensor Mount so that the narrowest slit is in line with the
opening to the sensor.
Connect one end of the DIN-to-DIN cable that is included with the High Sensitivity Light Sensor to the DIN
connector on the end of the sensor.
Mounting the Grating Mount
The threaded rod on the bottom of the Grating Mount has a lock washer and a wing nut. Remove the lock washer
and wing nut from the threaded rod, and screw the threaded rod into the short threaded post in the center of the
Degree Plate. Do not screw the Grating Mount all the way down onto the Light Sensor Arm. The Grating Mount
must be slightly above the Light Sensor
Arm so the Degree Plate can move.
Use the Light Sensor Arm to rotate the
Degree Plate until the zero line on the
Degree Plate is aligned with the index
mark on the Spectrophotometer Base.
Turn the Grating Mount so it is aligned
with the zero line on the Degree Plate and
the label side of the Grating Mount faces
away from the sensor on the Light Sensor
Arm.
Put the lock washer and wing nut back
onto the threaded rod and tighten the
wing nut until the Grating Mount remains
in place when the Degree Plate is rotated
in either direction (Fig. 12).
Mounting the Spectrophotometer Base
on the Optics Bench
You can mount the components of the
Spectrophotometer on the 1.2 meter Optics Bench that is part of the OS-8515 Basic Optics System, or the 0.6
meter (60 cm) Optics Bench that is included with the OS-8539 Spectrophotometer System. The Spectrophotom-
eter Base mounts into the T-slots on the sides of the Optics Bench and the Collimating Slits and Collimating Lens
snap into the center of the Optics Bench.
To mount the Spectrophotometer Base on the Optics
Bench, loosen the thumbscrew on each side of the
Base so the square nuts can slip into the T-slots on
the sides of the Optics Bench. Insert the square nuts
into the slots and slide the Base along the bench
until it is about 20 cm from the end (Fig 13).
Tighten the thumbscrews to hold the Base firmly on
the bench.
Rod Stand Mounting Clamps
You can adjust the height or angle of the Optics
Bench using the Rod Stand Mounting Clamps and
two rods and bases (not included). Each clamp has a
thumbscrew, a spacer (washer), and a square nut at
one end, and a second thumbscrew at the other end.
The thumbscrew with the square nut holds the
clamp onto the bench, and the other thumbscrew
Grating Mount
lock washer
wing nut
Screw the mount into
the threaded hole.
Fasten the mount
with the lock washer
and wing nut.
Figure 12: Grating Mount onto Rotating Table
Align the zero line on
the Degree Plate with
the index mark.
Line up the edge of
the Grating Mount
with the zero line.
zero line
Optics Bench
thumbscrew
square nut
T-slot
Spectrophotometer
Base hinge
Figure 13: Base Onto Optics Bench (End View)

9
012-06575A Educational Spectrophotometer
holds the clamp onto a rod.
Fixed Angle: To mount the clamp on the bench so it is parallel to the
bench (at a fixed angle), put the clamp on the bench with the spacer
on the opposite side of the clamp from the square nut. Tighten the
thumbscrew (Fig. 14).
Adjustable Angle: To mount the clamp on the bench so it can be
adjusted to any angle, move the spacer so it is next to the square nut.
Put the clamp on the bench with the square nut in the T-slot and the
spacer between the bench and the clamp. Adjust the clamp to the
angle you need and then tighten the thumbscrew (Fig 15).
Mounting and Adjusting the Collimating Slits and Lens
The Collimating Slits consist of two parts: the Collimating Slits Plate
and the Collimating Slits Holder. The slits are in a piece of metal that is
attached to a moveable slide. The slide is held on the Collimating Slits
Plate with a small thumbscrew and two permanently attached socket
screws. The Collimating Slits Plate is attached to the Collimating Slits
Holder with two brass thumbscrews. Loosen the small thumbcrew in the
Collimating Slits Plate in order to move the slits slide back and forth.
The narrow slot in the Collimating Slits Plate lets light through one slit
at a time. The top half of the Collimating Slits Plate helps to prevent
extra light from being measured.
Snap the Collimating Slits Holder into the Optics Bench near the end of
the bench that is closest to the light source you are using. To move the holder,
grasp the holder at the base and push in on the locking clip on one side of the
holder (Fig. 16). Slide the holder along the center section of the bench while
squeezing the clip. Release the clip to lock the holder firmly in position.
Snap the Collimating Lens Holder into the Optics Bench between the Collimat-
ing Slits Holder and the Spectrophotometer Base. Position the Collimating Lens
Holder about 10 cm from the Collimating Slits Holder.
Positioning the Collimating Slits and Lens
The focal length of the Collimating Lens is about 10 cm so the lens should be
positioned about 10 cm from the slits. Use the following procedure to position
the lens more precisely.
Set up a light source so that light from the source passes through one of the slits
on the Collimating Slits and then through the Collimating Lens. Rotate the
Light Sensor Arm so the Aperture Bracket and
Light Sensor are out of the way and the beam of
light can shine onto a distant vertical surface
such as a wall (Fig. 17).
Adjust the distance between the Collimating
Slits and the Collimating Lens so that the beam
of light is neither converging nor diverging (i.e.,
light rays are parallel). The beam of light should
stay about the same width all the way to the
distant vertical surface. Hold a piece of paper in
the light beam’s path at various distances along
square nut
spacer
thumbscrew
Optics Bench
clamp
Align the square nut
with the T-slot.
Figure 14: Mounting Clamp onto
Optics Bench - Fixed Angle
Optics Bench
square nut
Put the spacer
between the
bench and the
clamp. thumbscrew
clamp
Figure 15: Mounting Clamp onto
Optics Bench - Adjustable Angle
Degree Plate
GAIN
10
100
1
light sourceCollimating Slits
Collimating Lens
Light Sensor
Arm
light ray path
Figure 17: Collimation Setup
Collimating Slits
Optics Bench
locking clip
Figure 16: Locking Clip

10
Educational Spectrophotometer 012-06575A
the beam’s path. Check to see that the light beam’s width is about the same at each point along its path. Note that
the light may not be in focus during this process.
If the light beam is not perfectly vertical, loosen the small thumbscrew that holds the Collimating Slits slide and
adjust the slide, or loosen the brass thumbscrews that hold the Collimating Slits Plate onto the holder and adjust
the plate until the collimated beam is vertical. Remember to tighten the thumbscrews after you make the adjust-
ment.
The distances between the light source and the Collimating Slits and between the Collimating Slits and the rest of
the Spectrophotometer are not critical. However, the closer the light source, the brighter the spectrum.
Mounting the Grating
The Grating is mounted on one side of a rectangular glass plate.
There are two magnetic pads on the same side of the glass plate as the
Grating. These pads hold the Grating in place on the Grating Mount.
Once the light from the source is collimated, attach the Grating to the
Grating Mount so that the glass side of the Grating faces the light
source (Fig. 18).
Mounting and Positioning the Focusing Lens
The Degree Plate has markings on either side of the Light Sensor
Arm that indicate the appoximate position in which to place the
Focusing Lens. The Focusing Lens has two small magnets in its base
that hold it in place on top of the Light Sensor Arm. Place the Focus-
ing Lens on the Light Sensor Arm between the Grating Mount and
the High Sensitivity Light Sensor.
The Focusing Lens focal length is about 10 cm so the lens should be positioned on the Light Sensor Arm about 10
cm from the front of the Aperture Disk (Fig. 19).
Set up the light source, Collimating Slits, and
Collimating Lens so a beam of light shines through
the Grating and Focusing Lens. Darken the room so
you can see the spectral lines more clearly. Move the
Light Sensor Arm so the central ray of light (called
the “zeroth order”) is centered on the slit at the
bottom of the Aperture Disk. You should be able to
see the first order spectral lines on the Aperture
Screen on either side of the central ray of light.
Adjust the position of the Focusing Lens until the
spectral lines are sharply focused.
Note: Because the Grating is strongly blazed, the
spectral lines on one side of the central ray
(“zeroth order”) will be less bright than the
spectral lines on the other side.
10
1
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GAIN
HIGHSENSITIVITY
LIGHTSENSOR
CI-6604
Aperture Disk
Aperture Screen
Focusing Lens
Grating
Figure 19: Position Focusing Lens
Caution! Handle the Grating carefully. Avoid touching the Grating or the glass plate to which the
Grating is attached except by the edges of the glass plate.
Grating
Grating Mount
glass side faces light source
Figure 18: Grating Onto Mount

11
012-06575A Educational Spectrophotometer
Procedures
opaque cloth
light
source
binder clips
Figure 20: Mask the Light Source
CI-6604A
PASCO
scientific
HIGH SENSITIVITY
LIGHT SENSOR
opaque cloth
sunlight
binder clips
Collimating Slits
Figure 21: Mask the Spectrophotometer
Grounding
1. If you use an AC powered spectral light source, plug the power cord for the light source into a different outlet
than the outlet used for your ScienceWorkshop interface and computer.
2. For a very dim light source you may need to use the 100 GAIN setting on the High Sensitivity Light Sensor
and the 100x Sensitivity setting in the ScienceWorkshop program. If so, connect a wire from the Spectropho-
tometer Base to an earth ground in order to reduce electrical “noise”. You can use one of the small thumb-
screws from the Light Sensor Arm to connect a ground wire (not included) to the threaded hole on the side of
the Spectrophotometer Base opposite to the Rotary Motion Sensor.
Turning the Degree Plate
The spring in the hinge on the Spectrophotometer Base is strong enough to
keep the Pinion in contact with the edge of the Degree Plate as you move
the Light Sensor Arm to turn the plate. If the small diameter post on the
Pinion slips rather than turns, make sure that the thumbscrews that hold
the Rotary Motion Sensor onto the hinge are tight. You may need to
loosen the screws and then push the Rotary Motion Sensor so it is as close
to the Base as possible before re-tightening the screws.
Masking the Light Source or the Spectrophotometer
When using a bright spectral light source such as the PASCO Mercury
Vapor Light Source or the Low Pressure Sodium Light Source, cover the
source with an opaque cloth hood to block out ambient
light. Cover the light source opening with a mask that has
a 0.5 to 1.0 cm wide rectangular slot in it to reduce ghost
images. Use clothespins or binder clips to attach the edge
of the cloth hood to the plate on the Collimating Slits
(Fig. 20).
When measuring solar spectra, put an opaque cloth hood
over the entire Spectrophotometer so that the only open-
ing to the sunlight is the Collimating Slit. Use clothespins
or binder clips to attach the edge of the cloth hood to the
plate on the Collimating Slits. Use one hand to hold up
the center of the cloth hood (Fig. 21).
Using the ScienceWorkshop Program
Note: See the ScienceWorkshop User’s Guide for detailed information about using the ScienceWorkshop
program.
1. Start ScienceWorkshop. Select the Light Sensor to be connected to Analog Channel A and select the Rotary
Motion Sensor to be connected to Digital Channels 1 and 2.
2. In ScienceWorkshop, set the Rotary Motion Sensor so it can record 1440 divisions per rotation.
3. In the program, select a Graph display and set it to show “Light Intensity (% max)” on its vertical axis.
4. Use the Experiment Calculator in ScienceWorkshop to create a calculation of the actual angular position of the
Degree Plate. If the small post on the top of the Pinion is in contact with the edge of the Degree Plate, the
Angular Position of the Rotary Motion Sensor must be divided by the ratio of the radius of the Degree Plate

12
Educational Spectrophotometer 012-06575A
GAIN
10
100
1
Scan slowly and
continuously in one
direction.
High Sensitivity
Light Sensor
central ray
(“zeroth order”)
first order spectral lines
first order spectral lines
Diffraction
Grating
Figure 23: Scan the Spectrum
and the radius of the small post on the Pinion*.
The ratio is approximately 60 to 1. If the larger
diameter section at the bottom of the Pinion is
used, the Angular Position of the Rotary Motion
Sensor must be divided by 15* (Fig. 22).
5. Change the Graph display to show your calcula-
tion of Actual Angular Position on its horizontal
axis.
(*See “Calibrating the Degree Plate” earlier in the
Set Up section for more information on measuring
the ratio of the radius of the Degree Plate and the
radius of the Pinion.)
General Information About the Light Sensor
The High Sensivitiy Light Sensor has a GAIN (amplification) select switch on the top with three settings (1, 10
and 100). When you measure a spectrum, start with the lowest GAIN setting to measure the brightest lines. Then
switch to the next setting and re-scan the spectrum to measure the dimmer lines. Then re-scan again at the highest
GAIN setting to measure the dimmest lines.
It is also possible to amplify the signal from the Light Sensor using the ScienceWorkshop program. The normal
Sensitivity setting is “Low (1x)”. The other settings are “Medium (10x)” and “High (100x)”.
In general, you will record better data if you increase the GAIN setting on the Light Sensor before you increase
the Sensitivity setting in the ScienceWorkshop program.
General Information About Slit Widths
There are five slits on the Collimating Slits
slide and six slits on the Aperture Disk. You
can select wider slits in order to increase the
amount of light that passes through the
Grating and into the Light Sensor, but this will
make a wider spectral pattern and decrease the
accuracy of your measurements.
Scanning a Spectrum
To scan a spectrum, use the threaded post
under the Light Sensor to move the Light
Sensor Arm so the Light Sensor is beyond the
far end of the first order spectral lines, but not
in front of any of the spectral lines in the
second order.
In the ScienceWorkshop program, begin
recording data. Then, scan the spectrum
continuously but slowly in one direction by
pushing on the threaded post to rotate the Degree Plate. Scan all the way through the first order spectral lines on
one side of the central ray (“zeroth order”), through the central ray, and all the way through the first order spectral
lines on the other side of the central ray (Fig. 23).
The angle θof a particular line in the spectral pattern is one-half of the difference of the angle between the chosen
spectral line in the first order on one side of the central ray and the matching spectral line in the first order on the
Expression for the Angular Position
of the Rotary Motion Sensor Divide by 60 if the small post of the Pinion is used, or
put in the exact value of the
ratio of radii.
NOTE: The Experiment
Calculator for your version
of ScienceWorkshop may
differ in appearance. Refer
to your User’s Guide.
Figure 22: Create a Calculation

13
012-06575A Educational Spectrophotometer
Mercury spectrum
For example, measure
the difference in angle
between these two
lines. One-half of the
difference is the angle,
θ, to use for calculating
the wavelength, λ.
Figure 24: Measure the Angles for
Both First Order Spectral Patterns.
central ray
other side of the central ray. Use the built-in analysis tools in the ScienceWorkshop Graph display to find the angle
between the two matching spectral lines. The angle, θ, is one-half of the angle between the two lines. Use mλ= d
sin θ (and let the order, m, be 1) to calculate the wavelength of the chosen spectral line.
If a dim spectral line only appears on one side of the central ray (“zeroth order”), calculate where the central ray is
using a brighter spectral line that is visible on both sides of the central ray. Then determine the angle from the
central ray to the dim line to find the angle, θ, for that spectral line (Fig. 24).
Calibrating the Grating
The number of grating lines on the Grating is approximately 600 lines per millimeter. This translates to a Grating
line spacing of d = 1666 nm (1.666…x10-6 m).
To find the exact Grating line spacing, use a sodium lamp to calibrate the Grating. The average wavelength, λ, of
the yellow sodium doublet is 589.3 nm. Solving mλ= d sin θfor the line spacing, d, assuming m = 1 (for the first
order) gives
d = λ/sin θ
where λis the known wavelength of the sodium doublet. To determine the angle, θ, find the difference in angle
between the two first order yellow lines and divide by two.
Using the calibrated Grating line spacing, d, the wavelength of any spectral line in any other spectrum can be
more accurately determined using mλ= d sin θ where the order, m, is 0,1,2,…
Angular Resolution
When the Rotary Motion Sensor is fastened to the lower set of holes on the hinge on the Spectrophotometer Base
(as described earlier), the small diameter post of the Pinion will make contact with the edge of the Degree Plate.
The shaft of the Rotary Motion Sensor will rotate approximately 60 times for every rotation of the Degree Plate
(or 360˚). One rotation of the Rotary Motion Sensor shaft represents approximately 6˚ of angular displacement of
the Degree Plate. The maximum resolution of the Rotary Motion Sensor is 1440 divisions per rotation. Since one

14
Educational Spectrophotometer 012-06575A
rotation is 6˚, the angular resolution is 6˚ divided by 1440, or one quarter of a minute (0.25’) or fifteen seconds of
arc. This translates to a wavelength resolution of 2 nm, given a grating line spacing of approximately 1666 nm for
the Diffraction Grating included with the Spectrophotometer.
If the Rotary Motion Sensor is fastened to the upper set of holes on the hinge, the larger diameter part of the
Pinion will make contact with the edge of the Degree Plate. The shaft of the sensor will rotate 15 times for every
rotation of the Degree Plate. The maximum angular resolution is one minute or sixty seconds of arc. This trans-
lates to a wavelength resolution of 8 nm, given a grating line spacing of approximately 1666 nm.
Cuvettes
The Educational Spectrophotometer Accessory Kit includes two plastic cuvettes. These flat sided containers can
hold about five milliliters of liquid. You can use the Spectrophotometer and a cuvette to measure a substance’s
characteristic pattern of absorption and transmission.
To set up the Spectrophotometer and cuvette for measuring an absorption spectrum, do the following:
1. Unscrew the threaded post that holds the Light Sensor and Light
Sensor Mount onto the Light Sensor Arm.
2. Move the Light Sensor back so its threaded hole is lined up with
the rear centerline hole on the Light Sensor Mount. Use the
threaded post to reattach the Light Sensor and Light Sensor
Mount to the Light Sensor Arm.
3. Place the empty cuvette in front of the opening to the Light
Sensor between the sensor and the backside of the Aperture
Disk. Make sure that the cuvette is turned so that the smooth
sides are in line with the Light Sensor (Fig. 25).
4. Scan the spectrum from an incandescent light source (such as a
bulb powered by a regulated DC power supply).
5. Fill the cuvette with the liquid to be tested and then rescan the
spectrum of the incandescent light that is transmitted through the
liquid.
Other Information
The material on the front of the Aperture Disk may “fluoresce” under ultraviolet (UV) light. It may produce a
faint violet color when UV light shines on it. This faint violet color might be seen on the Aperture Disk when you
use a mercury light source, for example. The violet line of color appears to be a part of the spectral pattern when
the light falls on the disk, but disappears when the light falls only on the Aperture Screen. The High Sensitivity
Light Sensor cannot measure ultraviolet light.
The ScienceWorkshop program interprets the starting position of the Rotary Motion Sensor as the “zero” angular
(or linear) position. For some measurements it may be important to put a mark or stop on the edge of the Degree
Plate for reference so you can begin each trial of measurement from the same position. The Degree Plate has
several threaded holes near its outer edge. You can put one of the small thumbscrews that are stored on the Light
Sensor Arm into one of these threaded holes to use as a reference point for beginning or ending a scan.
CI-6604A
SENSOR
LIGHT
PASCO
HIGH SENSITIVITY
cuvette High Sensitivity
Light Sensor
Aperture Disk
threaded post
Light Sensor Arm
Figure 25: Cuvette with Light Sensor

15
012-06575A Educational Spectrophotometer
Activity 1: Emission (Bright Line) Spectrum
EQUIPMENT NEEDED
– Spectrophotometer System (OS-8539)
or
– Spectrophotometer Kit (OS-8537) – High Sensitivity Light Sensor (CI-6604)
– Rotary Motion Sensor (CI-6538) – Basic Optics Bench (part of OS-8515)
– Aperture Bracket (OS-8534)
and
– Mercury Vapor Light Source (OS-9286) – Large Rod Stand (ME-8735) (2)
– Rod, 45 cm (ME-8736) (2)
Introduction
The purpose of this activity is to determine the wavelengths of the colors in the spectrum of a mercury vapor
light.
Theory
An incandescent source such as a hot solid
metal filament produces a continuous spec-
trum of wavelengths. Light produced by an
electric discharge in a rarefied gas of a
single element contains a limited number of
discrete wavelengths - an emission or
“bright line” spectrum. The pattern of colors
in an emission spectrum is characteristic of
the element. The individual colors appear in
the shape of “bright lines” because the light
that is separated into the spectrum usually
passes through a narrow slit illuminated by
the light source.
A grating is a piece of transparent material on which has been ruled a large number of equally spaced parallel
lines. The distance between the lines is called the grating line spacing, d.
Light that strikes the transparent material is diffracted by the parallel lines. The diffracted light passes through
the grating at all angles relative to the original light path. If diffracted light rays from adjacent lines on the grat-
ing interfere and are in phase, an image of the light source can be formed. Light rays from adjacent lines will be
in phase if the rays differ in path length by an integral number of wavelengths of the light. The first place that an
image can be formed is where the path length between two adjacent light rays differs by one wavelength, λ.
However, the difference in path length for two adjacent light rays also depends on the grating line spacing, d,
and the angle, θ, at which the two light rays were diffracted by the grating.
The relationship between the wavelength of the light, λ, the grating line spacing, d, and diffraction angle, θ, is
as follows:
λ= d sin θ
In the diagram (Fig. 1.1), the path length for Ray A is one wavelength longer than the path length of Ray B.
Grating
d = grating line
spacing θ= angle of diffraction
path difference = λ = d sin θ
Ray A
Ray B
light rays
Figure 1.1: Ray diagram for first order diffraction pattern

16
Educational Spectrophotometer 012-06575A
Procedure
In this activity, the High Sensitivity Light Sensor measures the relative intensity of colors of light in an emission
spectrum produced by light from a mercury vapor light source passing through a grating. The Rotary Motion
Sensor measures the angle, θ, of each band or “bright line” of color.
The ScienceWorkshop program records and displays the light intensity and the angle. You can use the
program’s built-in data analysis tools to find the angle for each color, and then you can determine the wave-
length, λ, of each color.
Equipment Setup
1. Set up the Spectrophotometer next
to a mercury vapor light source as
shown (Fig. 1.2). If needed, use the
Rod Stand Mounting Clamps, two
rods, and two bases to raise the
Spectrophotometer to the same
level as the opening to the light
source. (Refer to the Introduction
for more information.)
2. If the light source has a large open-
ing, mask the opening so it trans-
mits a narrow (0.5 to 1.0 cm) beam
to the Collimating Slits. Put a cloth hood over the light source and attach the edge of the hood to the plate on the
Collimating Slits.
3. Turn on the light source. Once it is warmed up, adjust the light source, Collimating Slits, Collimating Lens, and
Focusing Lens so clear images of the central ray and the first order spectral lines appear on the Aperture Disk
and Aperture Screen in front of the High Sensitivity Light Sensor. Turn the Aperture Disk so the smallest slit on
the disk is in line with the central ray.
4. Connect the ScienceWorkshop interface to the computer, turn on the interface. Start Science Workshop.
5. Connect the High Sensitivity Light Sensor cable to Analog Channel A. Connect the Rotary Motion Sensor
cable to Digital Channels 1 and 2.
Experiment Setup
Select the Sensors, Set the Sample Rate, and Create a Calculation
• Refer to the User’s Guide for your version of ScienceWorkshop for detailed information on selecting sensors,
changing the sample rate, and creating a calculation.
1. In the ScienceWorkshop program, select the Rotary Motion Sensor and connect it to Digital Channels 1 and 2
and select the Light Sensor and connect it to Analog Channel A.
2. In the program, set up the Rotary Motion Sensor for high resolution (1440 Divisions per Rotation) and set the
sample rate to 20 Hz, or 20 measurements per second.
CI-6604A
PASCO
scientific
HIGH SENSITIVITY
LIGHT SENSOR
Light
Source
cloth
hood binder
clips
Collimating
Slits
Collimating
Lens
Grating
Rotary Motion
Sensor
Focusing Lens
High Sensitivity
Light Sensor
base
rod
Optics Bench
Figure 1.2: Equipment Setup