Download Solids and Light instructional units in one PDF fi PDF

TitleSolids and Light instructional units in one PDF fi
File Size762.1 KB
Total Pages82
Table of Contents
                            01Exploring LEDs Lamps
	Homework Question
02Exploring Light Patterns
	Light Patterns Emitted by Gas Lamps
	Light Emitted by the Clear Incandescent Lamp
	Homework Questions
03Intro Energy Diagrams
	Observations of Light
	Changing Energies — Transitions
	An Energy Model for the Atom
	Application Question
04Understanding the Spectra
	Homework Problem
05Applying Spectra-Diagrams
06Using Spectra to Search
07Using Gas Lamps
08Applying Energy Bands
09Energy Level - Model LEDs
10Applying Energy Level Mod
11Can Ohm's Law Explain
12 Meas Planck's Constant
Document Text Contents
Page 1



Exploring LEDs and Lamps

In this activity, you will explore the effect of changing the energy supplied
to incandescent lamps and light emitting diodes, then look for similarities
and differences among the different light sources.

Matter emits light through various processes that transform other forms of energy into
light. For example, a flame from a candle or fireplace during the burning process emits
light. The incandescent lamp — a light bulb — is a standard light source that is recogniz-
able by its characteristic shape and appearance. The light bulb contains a solid tungsten
filament that emits light when energy is provided by an external energy source such as a
battery or electrical power plant.

? Examine the incandescent lamp that you have been provided. Draw the location
of the filament and wires inside the lamp.

Voltage is a measure of energy being supplied to an electrical device like an incandescent
lamp. Although household incandescent lamps typically require a high voltage to oper-
ate, incandescent lamps such as the one that you have been supplied operate with low
voltages from a battery.

Another modern light source that requires low voltages is the light emitting diode (LED).
LEDs are typically used as on/off indicator lights in electrical appliances such as televi-
sions, VCR’s, video cameras, computers, and stereos. They are also used to display
numbers in some alarm clocks, radios, and microwave ovens. Another use is very large
video displays at sporting events and concerts. For example, the music group U2 during
its 1997 POPMART tour was using a 56 feet x 170 feet video screen consisting of LEDs. In
the 1997 movie, Batman & Robin, the Mr. Freeze costume worn by Arnold
Schwarzenegger consisted of 3,800 blue LEDs to illuminate his appearance. The low
voltage requirements needed to operate LEDs as well as their small size and mass make
them an attractive light source to use for these applications.

Name: Class:

LIGHT & Visual Quantum MechanicsVisual Quantum MechanicsVisual Quantum MechanicsVisual Quantum MechanicsVisual Quantum Mechanics

Kansas State University

@2001, Physics Education Research Group, Kansas State University. Visual Quantum Mechanics is
supported by the National Science Foundation under grants ESI 945782 and DUE 965288. Opinions
expressed are those of the authors and not necessarily of the Foundation.

Page 2


Examine the LEDs that you have been provided. Notice that the two connecting wires
have different lengths. These connecting wires are connected to the chip by very thin
wires inside the LED.

In this first activity, we will connect lamps and LEDs individually to an electrical energy
source and investigate the effects of changing the amount of electrical energy supplied
to them. The apparatus uses a small battery as an energy source. The amount of energy
reaching the lamp or LED is controlled by a potentiometer — a small rectangular device
with a screw on one end. Turning this screw changes the energy going to the lamp or
LED in the sockets. The apparatus used for these measurements are shown below.

Check the apparatus by inserting the incandescent lamp in its socket and connect the
battery to the battery clips. Adjust the meter in the circuit so that it will have a range of
about 0 - 9 Volts, and it will measure voltage. The incandescent lamp should come on
and the meter displays the voltage. If not, turn the screw on the potentiometer in the
counterclockwise direction until the light comes on. If the lamp still does not emit light,
check the connections or ask the instructor to help.

A diagram of the inside of an LED is shown in Figure 1-1. The chip at the heart of the
LED consists of two different solid materials that have been joined together. It is sur-
rounded by a transparent, hard plastic that protects the LED from vibration and shock.
The LED is constructed in such a way that the light emitted by the chip is reflected off
the base it sits on and is focused through the top of the LED. Thus, the light is bright-
est at the top of LEDs.

Figure 1-1: Schematic Diagram of an LED

Page 41



Using Spectra to Search for an Earth-like Planet

Now that we can explain why gas lamps emit their characteristic spectra
and how absorption spectra are related to emission, we will apply our
knowledge in a science fiction type scenario. The purpose will be to
identify the gases present on a mythical planet and determine whether
conditions similar to earth exist there.

To continue the study of spectra imagine we are a group of scientists in a star ship. Our
job is to look for planets that might be hospitable for humans. These plants are called
Class M on Star Trek. Lots of planets exist around other stars so it is a big job. If we
were to take the time needed to travel to each one – even at warp speed – and transport
down, we might never finish the job. In fact, we would not want to transport down until
we knew something about the atmosphere. So we need to investigate the gases in the
atmosphere from afar.

Fortunately, we have the perfect tool for learning about the atmosphere without needing
to get close to the planet. We can look at the light that passes through the atmosphere of
the planet and see what energy photons are absorbed by it. The basic arrangement is
shown in Figure 6-1.

@2001, Physics Education Research Group, Kansas State University. Visual Quantum Mechanics is
supported by the National Science Foundation under grants ESI 945782 and DUE 965288. Opinions
expressed are those of the authors and not necessarily of the Foundation.

Kansas State University

Figure 6-1: The arrangement of the starship, planet and a nearby star.

Name: Class:

LIGHT & Visual Quantum MechanicsVisual Quantum MechanicsVisual Quantum MechanicsVisual Quantum MechanicsVisual Quantum Mechanics

Page 42


? Our starship is equipped with very good spectroscopes. How would this arrange-
ment allow us to investigate the elements in the atmosphere of the planet?

The astronomers on our starship team bring data showing the spectra absorbed by the
planet’s atmosphere, as observed through a telescope that has a spectroscope attached.

Our task is to use the recorded spectra and compare them with those of some com-
monly known terrestrial gases. Then we can determine what gases are present in the
planet’s atmosphere. The spectra of various known gases are illustrated in Figure 6-2.



Carbon Dioxide:


Page 81


Now use equation (12-4) and our measurements to determine Planck’s constant. Construct
a graph of the measured threshold voltage versus the peak emission frequency for each
LED. Determine the slope of the resulting graph (∆V/∆F). Planck’s constant can be calcu-
lated by multiplying the resulting slope times the electronic charge, e, (1.6 x 10-19).

? What is your measured value for Planck’s constant?


(eV) λλλλ

(x 10-9 m) f

(1/s) V


Page 82


? The accepted value for the Planck ’s constant is 6.626 x 10 -34 Js. How does your
measured value of Planck ’s constant compare with the accepted value? Use the
following equation to compare these values,

h h


accepted measured



? What can explain the difference found between the measured and accept values of

Planck’s constant is a very important number that helps us determine the quantum nature
of both light and matter. German physicist Max Planck who used it to develop a model
that explained the photons of light (visible and invisible) emitted first introduced the
constant in 1900 by a warm (or hot) body like the sun or the filament of an incandescent
lamp. Albert Einstein in 1905 used the constant to develop a theory that explained the
phenomenon of electrons being ejected from a metal with kinetic energies determine by
the energy of photons of light shined on the metal. Today, Planck ’s constant is fundamen-
tal to any equation of quantum science.

Similer Documents