PASCO h/e Apparatus Instruction Manual

Includes

Teacher's Notes

and

Typical

Experiment Results

Instruction Manual
and Experiment Guide

012-04049J

for the PASCO scientific
Model AP-9368 and AP-9369

h/e Apparatus

and

h/e Apparatus Accessory Kit

08/98

© 1989 PASCO scientific $5.00

012-04049J h/e Apparatus and h/e Apparatus Accessory Kit

Table of Contents

Section Page

Copyright, Warranty, and Equipment Return.................................................. ii

Introduction ..................................................................................................... 1

Background Theory ......................................................................................... 2

Equipment and Setup ....................................................................................... 3

Equipment List .......................................................................................... 3

Installing the Batteries ...............................................................................3

Battery Voltage Check............................................................................... 3

Equipment Setup ....................................................................................... 4

Using the Accessory Kit Filters ................................................................. 6

Experiments:

Experiment 1: Wave Model vs Quantum Model................................. 7

Experiment 2: The Relationship of Energy, Wavelength

and Frequency............................................................ 11

Technical Information .................................................................................... 13

Theory of Operation ................................................................................. 13

Schematic Diagram................................................................................... 14

Teacher’s Guide.............................................................................................. 15

Technical Support ................................................................. Inside Back Cover

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i

h/e Apparatus and h/e Apparatus Accessory Kit 012-04049J

Copyright, Warranty, and Equipment Return

Please—Feel free to duplicate this manual
subject to the copyright restrictions below.

Copyright Notice

The PASCO scientific 012-04049J h/e Apparatus and
h/e Apparatus Accessory Kit manual is copyrighted
and all rights reserved. However, permission is granted
to non-profit educational institutions for reproduction
of any part of the manual providing the reproductions
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 the 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 workmanship. The 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 shipment
will not be covered by the warranty.) Shipping costs
for returning the equipment after repair will be paid by
PASCO scientific.

Equipment Return

Should the product have to be returned to PASCO
scientific for any reason, notify PASCO scientific by
letter, phone, or fax BEFORE returning the product.
Upon notification, the return authorization and ship­ping instructions will be promptly issued.

➤➤

➤

NOTE: NO EQUIPMENT WILL BE

➤➤

ACCEPTED FOR RETURN WITHOUT AN
AUTHORIZATION FROM PASCO.

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:

➀ The packing carton must be strong enough for the

item shipped.

➁ Make certain there are at least two inches of pack-

ing material between any point on the apparatus and
the inside walls of the carton.

➂ Make certain that the packing material cannot shift

in the box or become compressed, allowing the
instrument come in contact with the packing carton.

Address: PASCO scientific

10101 Foothills Blvd.
Roseville, CA 95747-7100

Phone: [phone]
FAX: [phone]
email: [e-mail]
web: www.pasco.com

Credits

This manual edited by: Dave Griffith

Teacher’s guide written by: Eric Ayar

ii

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012-04049J h/e Apparatus and h/e Apparatus Accessory Kit

Introduction

The emission and absorption of light was an early subject
for investigation by German physicist Max Planck. As
Planck attempted to formulate a theory to explain the
spectral distribution of emitted light based on a classical
wave model, he ran into considerable difficulty. Classical
theory (Rayleigh-Jeans Law) predicted that the amount of
light emitted from a black body would increase dramati­cally as the wavelength decreased, whereas experiment
showed that it approached zero. This discrepancy became
known as the ultraviolet catastrophe.

Experimental data for the radiation of light by a hot,
glowing body showed that the maximum intensity of
emitted light also departed dramatically from the clas­sically predicted values (Wien's Law). In order to rec­oncile theory with laboratory results, Planck was
forced to develop a new model for light called the
quantum model. In this model, light is emitted in
small, discrete bundles or quanta.

The relationship between the classical and quantum theo­ries for the emission of light can be investigated using the
PASCO scientific h/e Apparatus. Using the Apparatus in
combination with the PASCO Mercury Vapor Light
Source (Model OS-9286) allows an accurate determina­tion of the h/e ratio and thus a determination of h,
Planck's constant.

Figure 1. The h/e Apparatus Shown With the Accessory Kit and Mercury Vapor Light Source

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h/e Apparatus and h/e Apparatus Accessory Kit 012-04049J

Background Theory

Planck's Quantum Theory

By the late 1800's many physicists thought they had ex­plained all the main principles of the universe and discov­ered all the natural laws. But as scientists continued work­ing, inconsistencies that couldn't easily be explained be­gan showing up in some areas of study.

In 1901 Planck published his law of radiation. In it he
stated that an oscillator, or any similar physical system,
has a discrete set of possible energy values or levels; en­ergies between these values never occur.

Planck went on to state that the emission and absorption
of radiation is associated with transitions or jumps be­tween two energy levels. The energy lost or gained by the
oscillator is emitted or absorbed as a quantum of radiant
energy, the magnitude of which is expressed by the equa­tion:

E = h

ν

where E equals the radiant energy, ν is the frequency of
the radiation, and h is a fundamental constant of nature.
The constant, h, became known as Planck's constant.

Planck's constant was found to have significance beyond
relating the frequency and energy of light, and became a
cornerstone of the quantum mechanical view of the suba­tomic world. In 1918, Planck was awarded a Nobel prize
for introducing the quantum theory of light.

The Photoelectric Effect

In photoelectric emission, light strikes a material, causing
electrons to be emitted. The classical wave model pre­dicted that as the intensity of incident light was increased,
the amplitude and thus the energy of the wave would in­crease. This would then cause more energetic photoelec­trons to be emitted. The new quantum model, however,
predicted that higher frequency light would produce
higher energy photoelectrons, independent of intensity,
while increased intensity would only increase the number
of electrons emitted (or photoelectric current). In the
early 1900s several investigators found that the kinetic
energy of the photoelectrons was dependent on the wave­length, or frequency, and independent of intensity, while
the magnitude of the photoelectric current, or number of
electrons was dependent on the intensity as predicted by
the quantum model. Einstein applied Planck's theory and
explained the photoelectric effect in terms of the quantum
model using his famous equation for which he received
the Nobel prize in 1921:

E = h

ν

= KE

max

+ W

O

where KE
ted photoelectrons, and W
move them from the surface of the material (the work

is the maximum kinetic energy of the emit-

max

is the energy needed to re-

O

function). E is the energy supplied by the quantum of
light known as a photon.

The h/e Experiment

A light photon with energy hν is incident upon an elec­tron in the cathode of a vacuum tube. The electron uses a
minimum WO of its energy to escape the cathode, leaving
it with a maximum energy of KE
energy. Normally the emitted electrons reach the anode of
the tube, and can be measured as a photoelectric current.
However, by applying a reverse potential V between the
anode and the cathode, the photoelectric current can be
stopped. KE

can be determined by measuring the mini-

max

mum reverse potential needed to stop the photoelectrons
and reduce the photoelectric current to zero.* Relating
kinetic energy to stopping potential gives the equation:

KE

max

Therefore, using Einstein's equation,

ν

= Ve + W

h

When solved for V, the equation becomes:

V = (h/e)

If we plot V vs ν for different frequencies of light, the
graph will look like Figure 2. The V intercept is equal to -

W

/e and the slope is h/e. Coupling our experimental de-

O

termination of the ratio h/e with the accepted value for
e, 1.602 x 10

-19

coulombs, we can determine Planck's

constant, h.

Stopping

Potential

V

Figure 2. The graph of V vs.

*NOTE: In experiments with the PASCO h/e Ap­paratus the stopping potential is measured directly,
rather than by monitoring the photoelectric current.
See the Theory of Operation in the Technical Infor­mation section of the manual for details.

in the form of kinetic

max

= Ve

O

ν

- (WO/e)

Slope
= h/e

Frequency ν

νν

ν

νν

2

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012-04049J h/e Apparatus and h/e Apparatus Accessory Kit

Equipment and Setup

Equipment Required:

Lens/Grating
Assembly

Filters

h/e Apparatus AP-9368

Mercury Vapor light

Source OS-9286

Light Aperture
Assembly

– Digital voltmeter (SE-9589)
– h/e Apparatus, (AP-9368*)
– h/e Apparatus Accessory Kit, (AP-9369*)
– Mercury Vapor Light Source, (OS- 9286*)

Installing the Batteries

The h/e Apparatus requires two 9-volt batteries (supplied
but not installed). The battery compartment is accessed by
loosening the thumbscrew on the rear end panel, and re­moving the cover plate.

➤➤

➤ NOTE: The h/e Apparatus can also be powered

➤➤

using a ±9 V dual power supply. Just remove the
batteries and connect +9 V to the "+6 V MIN" bat­tery test terminal and -9 V to the "-6 V MIN" bat­tery test terminal.

Battery Voltage Check

Although the h/e Apparatus draws only a small amount of
current and batteries normally last a long time, it's a good
idea to check the output voltage before each use. Battery
test points are located on the side panel of the Apparatus
near the ON/OFF switch. Batteries functioning below the
recommended minimum operating level of 6 volts may
cause erroneous results in your experiments.

Support Base Assembly

Light Block (for
Light Source)

Coupling Bar Assembly

h/e Apparatus Accessory Kit AP-9369

Figure 3. h/e Equipment Identification

*These items may be purchased separately from PASCO

scientific, or together as an AP-9370 h/e System.

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To check the batteries, use a voltmeter to measure be­tween the OUTPUT ground terminal and each
BATTERY TEST terminal (-6V MIN and +6V MIN).
If either battery tests below its minimum rating, it should
be replaced before running experiments.

Battery Test
Terminals

ON/OFF
Switch

Ground
Te rm i na l

Figure 4. Battery Test Points

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