Name:
Date:
20.1 Benjamin Franklin
20.1
Benjamin Franklin overcame a lack of formal education to become a prominent businessman,
community leader, inventor, scientist, and statesman. His study of “electric fire” changed our basic
understanding of how electricity works.
An eye toward inventiveness
Benjamin Franklin was born
in Boston in 1706. With only
one year of schooling he
became an avid reader and
writer. He was apprenticed at
age 12 to his brother James, a
printer. The siblings did not
always see eye to eye, and at
17, Ben ran away to
Philadelphia.
In his new city, Franklin developed his own printing
and publishing business. Over the years, he became a
community leader, starting the first library, fire
department, hospital, and fire insurance company. He
loved gadgets and invented some of his own: the
Franklin stove, the glass armonica (a musical
instrument), bifocal eyeglasses, and swim fins.
‘Electric fire’
In 1746, Franklin saw some demonstrations of static
electricity that were meant for entertainment. He
became determined to figure out how this so-called
“electric fire” worked.
Undeterred by his lack of science education, Franklin
began experimenting. He generated static electricity
using a glass rod and silk cloth, and then recorded how
the charge could attract and repel lightweight objects.
Franklin read everything he could about this “electric
fire” and became convinced that a lightning bolt was a
large-scale example of the same phenomenon.
Father and son experiment
In June 1752, Franklin and his 21-year-old son,
William, conducted an experiment to test his theory.
Although there is some debate over the details, most
historians agree that Franklin flew a kite on a stormy
day in order to collect static charges.
Franklin explained that he and his son constructed a
kite of silk cloth and two cedar strips. They attached a
metal wire to the top. Hemp string was used to fly the
kite. A key was tied near the string’s lower end. A silk
ribbon was affixed to the hemp, below the key.
Shocking results
It is probable that Franklin and his son were under
some sort of shelter, to keep the silk ribbon dry. They
got the kite flying, and once it was high in the sky they
held onto it by the dry silk ribbon, not the wet hemp
string. Nothing happened for a while. Then they
noticed that the loose threads of the hemp suddenly
stood straight up.
The kite probably was not struck directly by lightning,
but instead collected charge from the clouds. Franklin
touched his knuckle to the key and received a static
electric shock. He had proved that lightning was a
discharge of static electricity.
Those are charged words
Through his experiments, Franklin determined that
“electric fire” was a single “fluid” rather than two
separate fluids, as European scientists had thought.
He proposed that this “fluid” existed in two states,
which he called “positive” and “negative.” Franklin
was the first to explain that if there is an excess
buildup of charge on one item, such as a glass rod, it
must be exactly balanced by a lack of charge on
another item, such as the silk cloth. Therefore, electric
charge is conserved. He also explained that when there
is a discharge of static electricity between two items,
the charges become balanced again.
Many of Franklin’s electrical terms remain in use
today, including battery, charge, discharge, electric
shock, condenser, conductor, plus and minus, and
positive and negative.
Page 2 of 2
Reading reflection
20.1
1.
Although Ben Franklin had only one year of schooling, he became a highly educated person.
Describe how Franklin learned about the world.
2.
What hypothesis did Franklin test with his kite experiment?
3.
Describe the results and conclusion of Franklin’s kite experiment.
4.
Franklin’s kite experiment was dangerous. Explain why.
5.
Silk has an affinity for electrons. When you rub a glass rod with silk, the glass is left with a positive charge.
Make a diagram that shows the direction that charges move in this example. Illustrate and label positive and
negative charges on the silk and glass rod in your diagram. Note: Show the same number of positive and
negative charges in your diagram.
6.
Research: Among Franklin’s many inventions is the lightning rod. Find out how this device works, and
create a model or diagram to show how it functions.
Name:
20.2 Open and Closed Circuits
Date:
20.2
Where is the current flowing?
You have built and tested different kinds of circuits in the lab. Now you can use what you learned to make
predictions about circuits you haven’t seen before. Use the circuit diagrams pictured below to answer the
questions. You may wish to write on the diagrams in order to keep track where the current is flowing. As a result,
each diagram is repeated several times.
1.
Which devices (A, B, C, or D) in the circuit pictured below will be on when the following conditions are
met? For your answer, give the letter of the device or devices.
a. Switch 3 is open, and all other switches are closed.
b. Switch 2 is open, and all other switches are closed.
c. Switch 4 is open, and all other switches are closed.
d. Switch 1 is open, and all other switches are closed.
e. Bulb C blows out, and all switches are closed.
f. Bulb A blows out, and all switches are closed.
.
g. Switches 2 and 4 are open, and switches 1 and 3 are closed.
h. Switches 2 and 3 are open, and switches 1 and 4 are closed.
Page 2 of 3
.
20.2
i. Switches 2, 3, and 4 are open, and switch 1 is closed.
j. Switches 1 and 2 are open, and switches 3 and 4 are closed.
2. Which of the devices (A-G) in the circuit below will be on when the following conditions are met? For your
answer, give the letter of the device or devices.
a. Switch 5 is open, and all other switches are closed.
b. Switch 6 is open, and all others are closed.
c. Switch 7 is open, and all others are closed.
.
d. Switch 4 is open, and all others are closed.
e. Switch 3 is open, and all others are closed.
f. Switch 2 is open, and all others are closed.
g. Switch 1 is open, and all others are closed.
h. Switches 2 and 4 are open, and all others are closed.
Page 3 of 3
i. Switches 4 and 6 are open, and all others are closed.
20.2
j. Switches 4 and 7 are open, and all others are closed.
k. Switches 5 and 7 are open, and all others are closed.
l. Switches 2 and 3 are open, and all others are closed.
m. Bulb D blows out with all switches closed.
.
n. Bulbs A and B blow out with all switches closed.
o. Bulbs A and D blow out with all switches closed.
3. Use arrows to draw the direction of the current in each of the circuits below. Make sure to show current
direction in all paths of the circuits within each diagram.
4.
5.
How many possible paths are there in circuit diagrams in questions (1) and (2)?
Draw a circuit of your own. Use one battery, show at least 4 devices (bulbs and bells), and divide the current
at some point in the circuit. Finally, use arrows to show the direction of the current in all parts of your circuit.
Name:
20.3 Using an Electric Meter
Date:
20.3
What do you measure in a circuit and how do you measure it? This skill sheet gives you useful tips to help you
use an electric meter and understand electrical measurements.
The digital multimeter
Most people who work with electric circuits use a digital multimeter to measure electrical quantities. These
measurements help them analyze circuits. Most multimeters measure voltage, current, and resistance. A typical
multimeter is shown below:
Page 2 of 4
Using the digital multimeter
This table summarizes how to use and interpret any digital meter in a battery circuit. Note: A component
is any part of a circuit, such as a battery, a bulb, or a wire.
20.3
Measuring Voltage
Measuring Current
Measuring Resistance
Circuit is ON
Circuit is ON
Circuit is OFF
Turn dial to voltage, labeled
Turn dial to current, labeled
Turn dial to resistance, labeled Ω
Connect leads to meter following
meter instructions
Connect leads to meter following
meter instructions
Connect leads to meter following
meter instructions
Place leads at each end of
component (leads are ACROSS
the component)
Break circuit and place leads on
each side of the break (meter is IN
the circuit)
Place leads at each end of
component (leads are ACROSS
the component)
Measurement in VOLTS (V)
Measurement in AMPS (A)
Measurement in OHMS (Ω)
Battery measurement shows
relative energy provided
Measurement shows the value of
current at the point where meter is
placed
Measurement shows the
resistance of the component
Component measurement shows
relative energy used by that
component
Current is the flow of charge
through the wire
When the resistance is too high,
the display shows OL (overload)
or ∝ (infinity)
Page 3 of 4
20.3
Build a series circuit with 2 batteries and 2 bulbs.
1.
Measure and record the voltage across each battery:
2.
Measure and record the voltage across each bulb:
3.
Measure and record the voltage across both batteries:
4.
Draw a circuit diagram or sketch that shows all the posts in the circuit (posts are where wires and holders
connect together).
5.
Break the circuit at one post. Measure the current and record the value below. Repeat until you have
measured the current at every post.
Page 4 of 4
6.
Create a set of instructions on how to use the meter to do a task. Find someone unfamiliar with the
meter. See if he or she can follow your instructions.
20.3
7.
A fuse breaks a circuit when current is too high. A fuse must be replaced when it breaks a circuit. Explain
how measuring the resistance of a fuse can tell you if it is defective.
8.
You suspect that a wire is defective but can't see a break in it. Explain how measuring the resistance of the
wire can tell you if it has a break.
Name:
Date:
20.4 Voltage, Current, and Resistance
20.4
Electricity is one of the most fascinating topics in physical science. It’s also one of the most useful to understand,
since we all use electricity daily. This skill sheet reviews some of the important terms in the study of electricity.
In the reading section, you’ll find questions that check your understanding. If you’re not sure of the answer, go
back and read that section again. In the practice section, you will have an opportunity to show that you know how
voltage, current, and resistance are related in real-world situations.
What is voltage?
You know that water will flow from a higher tank through a hose into a
lower tank. The water in the higher tank has greater potential energy than the
water in the lower tank. A similar thing happens with the flow of charges in
an electric circuit.
Charges flow in a circuit when there is a difference in energy level from one
end of the battery (or any other energy source) to the other. This energy
difference is measured in volts. The energy difference causes the charges to
move from a higher to a lower voltage in a closed circuit.
Think of voltage as the amount of “push” the electrical source supplies to the
circuit. A meter is used to measure the amount of energy difference or
“push” in a circuit. The meter reads the voltage difference (in volts) between
the positive and the negative ends of the power source (the battery). This
voltage difference supplies the energy to make charges flow in a circuit.
1.What is the difference between placing a 1.5-volt battery in a circuit and
placing a 9-volt battery in a circuit?
What is current?
Current describes the flow of electric charges. Current is the actual measure of how many charges are flowing
through the circuit in a certain amount of time. Current is measured in units called amperes.
Just as the rate of water flowing out of a faucet can be fast or slow, electrical current can move at different rates.
The type, length, and thickness of wire all effect how much current flows in a circuit. Resistors slow the flow of
current. Adding voltage causes the current to speed up.
2.
What could you do to a closed circuit consisting of a battery, a light bulb, and a switch that would increase
the amount of current? Explain your answer.
3.
What could you do to a closed circuit consisting of a battery, a light bulb, and a switch that would decrease
the amount of current? Explain your answer.
Page 2 of 3
What is resistance?
20.4
Resistance is the measure of how easily charges flow through a circuit. High resistance means it is
difficult for charges to flow. Low resistance means it is easy for charges to flow. Electrical resistance is measured
in units called ohms (abbreviated with the symbol Ω).
Resistors are items that reduce the flow of charge in a circuit. They act like “speed bumps” in a circuit. A light
bulb is an example of a resistor.
4.
Describe one thing that you could do to the wire used in a circuit to decrease the amount of resistance
presented by the wire.
How are voltage, current, and resistance related?
When the voltage (push) increases, the current (flow of charges) will also increase, and when the voltage
decreases, the current likewise decreases. These two variables, voltage and current, are said to be directly
proportional.
When the resistance in an electric circuit increases, the flow of charges (current) decreases. These two variables,
resistance and current, are said to be inversely proportional. When one goes up, the other goes down, and vice
versa.
The law that relates these three variables is called Ohm’s Law. The formula is:
Voltage (volts)
Current (amps) = ---------------------------------------------Resistance (ohms, Ω)
5.
In your own words, state the relationship between resistance and current, as well as the relationship between
voltage and current.
•
In a circuit, how many amps of current flow through a resistor such as a 6-ohm light bulb when using four
1.5-volt batteries as an energy supply?
Solution:
4 × 1.5 volts 6 volts
Current = --------------------------- = --------------6 ohms
6 ohms
Current = 1 amp
Page 3 of 3
20.4
Now you will have the opportunity to demonstrate your understanding of the relationship between current,
voltage and resistance. Answer each of the following questions and show your work.
1.
How many amps of current flow through a circuit that includes a 9-volt battery and a bulb with a resistance
of 6 ohms?
2.
How many amps of current flow through a circuit that includes a 9-volt battery and a bulb with a resistance
of 12 ohms?
3.
How much voltage would be necessary to generate 10 amps of current in a circuit that has 5 ohms of
resistance?
4.
How many ohms of resistance must be present in a circuit that has 120 volts and a current of 10 amps?
Name:
Date:
20.4 Ohm’s Law
20.4
A German physicist, Georg S. Ohm, developed this mathematical relationship, known as Ohm’s Law, which is
present in most circuits. It states that if the voltage in a circuit increases, so does the current. If the resistance
increases, the current decreases.
Voltage (volts)
Current (amps) = ---------------------------------------------Resistance (ohms, Ω)
To work through this skill sheet, you will need the symbols used to depict circuits in
diagrams. The symbols that are most commonly used for circuit diagrams are
provided to the right.
If a circuit contains more than one battery, the total voltage is the sum of the
individual voltages. A circuit containing two 6 V batteries has a total voltage of 12 V.
[Note: The batteries must be connected positive to negative for the voltages to add.]
•
If a toaster produces 12 ohms of resistance in a 120-volt circuit, what is the
amount of current in the circuit?
Solution:
I =
V 120 volts
=
= 10 amps
R
12 ohms
The current in the toaster circuit is 10 amps.
Note: If a problem asks you to calculate the voltage or resistance, you must rearrange the equation to solve for V
or R. All three forms of the equation are listed below.
I =
V
R
V = IR
R =
V
I
Answer the following question using Ohm’s law. Don’t forget to show your work.
1.
How much current is in a circuit that includes a 9-volt battery and a bulb with a resistance of 3 ohms?
2.
How much current is in a circuit that includes a 9-volt battery and a bulb with a resistance of 12 ohms?
3.
A circuit contains a 1.5 volt battery and a bulb with a resistance of 3 ohms. Calculate the current.
4.
A circuit contains two 1.5 volt batteries and a bulb with a resistance of 3 ohms. Calculate the current.
5.
What is the voltage of a circuit with 15 amps of current and toaster with 8 ohms of resistance?
6.
A light bulb has a resistance of 4 ohms and a current of 2 A. What is the voltage across the bulb?
Page 2 of 2
7.
How much voltage would be necessary to generate 10 amps of current in a circuit that has 5 ohms
of resistance?
8.
How many ohms of resistance must be present in a circuit that has 120 volts and a current of 10
amps?
9.
An alarm clock draws 0.5 A of current when connected to a 120 volt circuit. Calculate its resistance.
20.4
10. A portable CD player uses two 1.5 V batteries. If the current in the CD player is 2 A, what is its resistance?
11. You have a large flashlight that takes 4 D-cell batteries. If the current in the flashlight is 2 amps, what is the
resistance of the light bulb? (Hint: A D-cell battery has 1.5 volts.)
12. Use the diagram below to answer the following problems.
a.
What is the total voltage in each circuit?
b.
How much current would be measured in each circuit if the light bulb has a resistance of 6 ohms?
c.
How much current would be measured in each circuit if the light bulb has a resistance of 12 ohms?
d.
Is the bulb brighter in circuit A or circuit B? Why?
13. What happens to the current in a circuit if a 1.5-volt battery is removed and is replaced by a 9-volt battery?
14. In your own words, state the relationship between resistance and current in a circuit.
15. In your own words, state the relationship between voltage and current in a circuit.
16. What could you do to a closed circuit consisting of 2 batteries, 2 light bulbs, and a switch to increase the
current? Explain your answer.
17. What could you do to a closed circuit consisting of 2 batteries, 2 light bulbs, and a switch to decrease the
current? Explain your answer.
18. You have four 1.5 V batteries, a 1 Ω bulb, a 2 Ω bulb, and a 3 Ω bulb. Draw a circuit you could build to
create each of the following currents. There may be more than one possible answer for each.
a.
1 ampere
b.
2 amperes
c.
3 amperes
d.
6 amperes
Name:
Date:
21.1 Series Circuits
21.1
In a series circuit, current follows only one path from the positive end of the battery toward the negative end. The
total resistance of a series circuit is equal to the sum of the individual resistances. The amount of energy used by
a series circuit must equal the energy supplied by the battery. In this way, electrical circuits follow the law of
conservation of energy. Understanding these facts will help you solve problems that deal with series circuits.
To answer the questions in the practice section, you will have to use Ohm's law. Remember that:
Voltage (volts)
Current (amps) = --------------------------------------Resistance (ohms)
Some questions ask you to calculate a voltage drop. We often say that each resistor (or light bulb) creates a
separate voltage drop. As current flows along a series circuit, each resistor uses up some energy. As a result, the
voltage gets lower after each resistor. If you know the current in the circuit and the resistance of a particular
resistor, you can calculate the voltage drop using Ohm’s law.
Voltage drop across resistor (volts) = Current through resistor (amps) × Resistance of one resistor (ohms)
1.
2.
Use the series circuit pictured to the right to answer
questions (a)–(e).
a.
What is the total voltage across the bulbs?
b.
What is the total resistance of the circuit?
c.
What is the current in the circuit?
d.
What is the voltage drop across each light bulb?
(Remember that voltage drop is calculated by
multiplying current in the circuit by the resistance of a
particular resistor: V = IR.)
e.
Draw the path of the current on the diagram.
Use the series circuit pictured to the right to answer
questions (a)–(e).
a.
What is the total voltage across the bulbs?
b.
What is the total resistance of the circuit?
c.
What is the current in the circuit?
d.
What is the voltage drop across each light bulb?
e.
Draw the path of the current on the diagram.
3.
What happens to the current in a series circuit as more light bulbs are added? Why?
4.
What happens to the brightness of each bulb in a series circuit as additional bulbs are added? Why?
Page 2 of 2
5.
6.
7.
8.
9.
Use the series circuit pictured to the right to
answer questions (a), (b), and (c).
a.
What is the total resistance of the circuit?
b.
What is the current in the circuit?
c.
What is the voltage drop across each resistor?
Use the series circuit pictured to the right to
answer questions (a)–(e).
a.
What is the total voltage of the circuit?
b.
What is the total resistance of the circuit?
c.
What is the current in the circuit?
d.
What is the voltage drop across each light bulb?
e.
Draw the path of the current on the diagram.
Use the series circuit pictured right to answer questions
(a), (b), and (c). Consider each resistor equal to all others.
a.
What is the resistance of each resistor?
b.
What is the voltage drop across each resistor?
c.
On the diagram, show the amount of voltage in the
circuit before and after each resistor.
Use the series circuit pictured right to answer questions (a)–
(d).
a.
What is the total resistance of the circuit?
b.
What is the current in the circuit?
c.
What is the voltage drop across each resistor?
d.
What is the sum of the voltage drops across the three
resistors? What do you notice about this sum?
Use the diagram to the right to answer
questions (a), (b), and (c).
a.
How much current would be measured
in each circuit if each light bulb has a
resistance of 6 ohms?
b.
How much current would be measured
in each circuit if each light bulb has a
resistance of 12 ohms?
c.
What happens to the amount of current
in a series circuit as the number of
batteries increases?
21.1
Page 1 of 2
21.1 George Westinghouse
21.1
George Westinghouse was both an imaginative tinkerer and a bold entrepreneur. His inventions had a
profound effect on nineteenth-century transportation and industrial development in the United States. His air
brakes and signaling systems made railway systems safer at higher speeds, so that railroads became a
practical method of transporting goods across the country. He promoted alternating current as the best means of
providing electric power to businesses and homes, and his method became the worldwide standard.
Westinghouse obtained 361 patents over the course of his life.
A boyhood among machines
George Westinghouse was born
October 6, 1846, in Central Bridge,
New York. When he was 10, his family
moved to Schenectady, where his
father opened a shop that
manufactured agricultural machinery.
George spent a great deal of time working and
tinkering there.
After serving in both the Union Army and Navy in the
Civil War, Westinghouse attended college for three
months. He dropped out after receiving his first patent
in 1865, for a rotary steam engine he had invented in
his father’s shop.
An inventive train of thought
In 1866, Westinghouse was aboard a train that had to
come to a sudden halt to avoid colliding with a
wrecked train. To stop the train, brakemen manually
applied brakes to each individual car based on a signal
from the engineer.
Westinghouse believed there could be a safer way to
stop these heavy trains. In April 1869, he patented an
air brake that enabled the engineer to stop all the cars
in tandem. That July he founded the Westinghouse Air
Brake Company, and soon his brakes were used by
most of the world’s railways.
The new braking system made it possible for trains to
travel safely at much higher speeds. Westinghouse
next turned his attention to improving railway
signaling and switching systems. Combining his own
inventions with others, he created the Union Switch
and Signal Company.
Long-distance electricity
Next, Westinghouse became interested in transmitting
electricity over long distances. He saw the potential
benefits of providing electric power to individual
homes and businesses, and in 1884 formed the
Westinghouse Electric Company. Westinghouse
learned that Nikola Tesla had developed alternating
current and he persuaded Tesla to join the company.
Initially, Westinghouse met with resistance from
Thomas Edison and others who argued that direct
current was a safer alternative. But direct current
could not be transmitted over distances longer than
three miles. Westinghouse demonstrated the potential
of alternating current by lighting the streets of
Pittsburgh, Pennsylvania, and, in 1893, the entire
Chicago World’s Fair. Afterward, alternating current
became the standard means of transmitting electricity.
From waterfalls to elevated railway
Also in 1893, Westinghouse began yet another new
project: the construction of three hydroelectric
generators to harness the power of Niagara Falls on
the New York-Canada border. By November 1895,
electricity generated there was being used to power
industries in Buffalo, some 20 miles away.
Another Westinghouse interest was alternating current
locomotives. He introduced this new technology first
in 1905 with the Manhattan Elevated Railway in New
York City, and later with the city’s subway system.
An always inquiring mind
The financial panic of 1907 caused Westinghouse to
lose control of his companies. He spent much of his
last years in public service. Westinghouse died in 1914
and left a legacy of 361 patents in his name—the final
one received four years after his death.
Page 2 of 2
Reading reflection
21.1
1.
Where did George Westinghouse first develop his talent for inventing things?
2.
How did Westinghouse make it possible for trains to travel more safely at higher speeds?
3.
Why did Westinghouse promote alternating current over direct current for delivering electricity to
businesses and homes?
4.
How did Westinghouse turn public opinion in favor of alternating current?
5.
Together with a partner, explain the difference between direct and alternating current. Write your
explanation as a short paragraph and include a diagram.
6.
How did Westinghouse provide electrical power to the city of Buffalo, New York?
7.
Ordinary trains in Westinghouse’s time were coal-powered steam engines. How were Westinghouse’s
Manhattan elevated trains different?
8.
Research: Westinghouse had a total of 361 patents to his name. Use a library or the Internet to find out about
three inventions not mentioned in this brief biography, and describe each one.
Name:
21.1 Thomas Edison
Date:
21.1
Thomas Alva Edison holds the record for the most patents issued to an individual in the United States:
1,093. He is famous for saying that “Genius is one percent inspiration and ninety-nine percent perspiration.”
Edison’s hard work and imagination brought us the phonograph, practical incandescent lighting, motion pictures,
and the alkaline storage battery.
The young entrepreneur
Thomas Alva Edison was born
February 11, 1847, in Milan, Ohio, the
youngest of seven children. His family
moved to Port Huron, Michigan, in
1854 and Thomas attended school
there—for a few months. He was
taught reading, writing, and simple arithmetic by his
mother, a former teacher, and he read widely and
voraciously. The basement was his first laboratory.
The concept of a commercial research facility—an
“invention factory” of sorts—was new. Some consider
Menlo Park itself to be one of Edison’s most important
inventions.
When he was 13, Thomas started selling newspapers
and candy on the train from Port Huron to Detroit.
Waiting for the return train, he often read science and
technology books. He set up a chemistry lab in an
empty boxcar, until he accidentally set the car on fire.
In 1888, Edison opened an even larger research
complex in West Orange, New Jersey. Here he
improved the phonograph and created a device that
“does for the eye what the phonograph does for the
ear.” This was the first motion picture player.
At 16, Thomas learned to be a telegraph operator and
began to travel the country for work. His interest in
experiments and gadgets grew and he invented an
automatic timer to send telegraph messages while he
slept. About this time his hearing was deteriorating; he
was left with only about 20 percent hearing in one ear.
First a patent, then business
In 1868 Edison arrived in Boston. His first patent was
issued there for an electronic vote recorder. While the
device worked very well, it was a commercial failure.
Edison vowed that, in the future, he would only invent
things he was certain the public would want.
He moved on to New York, where he invented a
“Universal Stock Printer” for which he was paid
$40,000, a huge sum he found hard to comprehend.
After developing some devices to improve telegraph
communications, Edison had enough money to build a
research lab in Menlo Park, New Jersey.
The invention factory
Edison’s facility had everything he needed for
inventing: machine and carpentry shops, a lab, offices,
and a library. He hired assistants who specialized
where he felt he was lacking, in mathematics, for
instance.
It was there Edison invented the tin foil phonograph,
the first machine to record and play back sounds.
Next, he developed a practical, safe, and affordable
incandescent light. The company he formed to
manufacture and market this invention eventually
became General Electric.
Not a man to be discouraged
Not all of Edison’s ideas were successful. In the 1890s
he sold all his stock in General Electric and invested
millions to develop better methods of mining iron ore.
He never was able to come up with a workable process
and the investment was a loss.
One of the most remarkable aspects of Edison’s
character was his refusal to be discouraged by failure.
The 3,500 notebooks he kept illustrate his typical
approach to inventing: brainstorm as many avenues as
possible to create a product, try anything that seems
remotely workable, and record everything. Failed
experiments, he said, helped direct his thinking toward
more useful designs.
Edison also worked to create an efficient storage
battery to use in electric cars. By the time his alkaline
battery was ready, electric cars were uncommon. But
the invention proved useful in other devices, like
lighting railway cars and miners’ lamps. Edison’s last
patent was granted when he was 83, the year before he
died, and his last big undertaking was an attempt, at
Henry Ford’s request, to develop an alternative source
of rubber. He was still working on the project when he
died in 1931.
Page 2 of 2
Reading reflection
21.1
1.
Name three different avenues by which Thomas Edison received an education.
2.
What did Edison learn from his attempts to sell his first patented invention?
3.
Describe Edison’s “invention factory.”
4.
Name two important inventions that came out of Menlo Park.
5.
Describe the process Edison used to invent things.
6.
How did Edison view his projects that failed?
7.
How do you think the tin foil phonograph worked? Discuss and compare your ideas with a fellow member of
your class.
8.
Research: Edison holds the record for the most patents issued to an individual in the United States. Use a
library or the Internet to research three of his inventions that are not mentioned in this biography, and briefly
describe each one.
Name:
Date:
21.2 Parallel Circuits
21.2
A parallel circuit has at least one point where the circuit divides, creating more than one path for current. Each
path is called a branch. The current through a branch is called branch current. If current flows into a branch in a
circuit, the same amount of current must flow out again. This rule is known as Kirchoff’s current law.
Because each branch in a parallel circuit has its own path to the battery, the voltage across each branch is equal to
the battery’s voltage. If you know the resistance and voltage of a branch you can calculate the current with Ohm’s
Law (I = V/R).
1.
2.
3.
4.
Use the parallel circuit pictured right to answer
questions (a)–(d).
a.
What is the voltage across each bulb?
b.
What is the current in each branch?
c.
What is the total current provided by the battery?
d.
Use the total current and the total voltage to
calculate the total resistance of the circuit.
Use the parallel circuit pictured right to answer
questions (a)–(d).
a.
What is the voltage across each bulb?
b.
What is the current in each branch?
c.
What is the total current provided by the battery?
d.
Use the total current and the total voltage to
calculate the total resistance of the circuit.
Use the parallel circuit pictured right to answer
questions (a)–(d).
a.
What is the voltage across each resistor?
b.
What is the current in each branch?
c.
What is the total current provided by the
batteries?
d.
Use the total current and the total voltage to calculate the total resistance of the circuit.
Use the parallel circuit pictured right to answer
questions (a)–(c).
a.
What is the voltage across each resistor?
b.
What is the current in each branch?
c.
What is the total current provided by the
battery?
Page 2 of 2
21.2
In part (d) of problems 1, 2, and 3, you calculated the total resistance of each circuit. This required you to first
find the current in each branch. Then you found the total current and used Ohm’s law to calculate the total
resistance. Another way to find the total resistance of two parallel resistors is to use the formula shown below.
R to ta l =
R1 × R 2
R1 + R 2
Calculate the total resistance of a circuit containing two 6 ohm resistors.
Given
The circuit contains two 6 Ω resistors in parallel.
Looking for
The total resistance of the circuit.
Relationships
R to ta l =
1.
2.
Solution
6Ω×6Ω
6Ω +6Ω
= 3Ω
R to ta l =
R to ta l
The total resistance is 3 ohms.
R1 × R 2
R1 + R 2
Calculate the total resistance of a circuit containing each of the following combinations of resistors.
a.
Two 8 Ω resistors in parallel
b.
Two 12 Ω resistors in parallel
c.
A 4 Ω resistor and an 8 Ω resistor in parallel
d.
A 12 Ω resistor and a 3 Ω resistor in parallel
To find the total resistance of three resistors A, B, and C in parallel, first use the formula to find the total of
resistors A and B. Then use the formula again to combine resistor C with the total of A and B. Use this
method to find the total resistance of a circuit containing each of the following combinations of resistors.
a.
Three 8 Ω resistors in parallel
b.
Two 6 Ω resistors and a 2 Ω resistor in parallel
c.
A 1 Ω, a 2 Ω, and a 3 Ω resistor in parallel
Name:
Date:
21.2 Lewis Latimer
21.2
Latimer, often called a “Renaissance Man,” was an accomplished African-American inventor receiving
seven U.S. patents. His professional and personal achievements define him as a humanitarian, artist, and scientist.
Son of former slaves
An enlightened inventor
Lewis Howard Latimer
was born on September 4,
1848 in Chelsea,
Massachusetts. Latimer's
parents had escaped from
slavery in Virginia and
moved north. In Boston,
Latimer's father, George,
was arrested and jailed
because he was considered
a fugitive. The
Massachusetts Supreme Court ruled that he belonged
to his owner in Virginia.
Latimer was not only a talented draftsman, but also a
successful inventor. While at Crosby and Gould, he
developed his first invention—mechanical improvements
for railroad train water closets (also known as toilets!).
The people of Boston protested and local supporters
paid for his release. George was free. George and his
wife settled in Chelsea where they started their family.
In 1858, George, fearing he would be forced to return
to slavery, went into hiding, leaving his family behind.
Young Lewis Latimer attended grammar school in
Chelsea and was a high-achieving student. As a
teenager, Lewis lied about his age to join the Union
Navy during the Civil War. After four years of military
service, the war ended and Latimer was honorably
discharged.
Drafting a career
Latimer looked for work in Boston and finally found a
job as an office boy with a patent law firm, Crosby and
Gould. He earned $3.00 per week. At the firm, Lewis
studied the detailed patent drawings prepared by the
draftsmen. Over time, he taught himself the drafting
trade using the tools and books available there.
Latimer showed his drawings to his boss and secured a
job as a draftsman earning $20.00 per week. He
eventually became chief draftsman and worked at the
firm for eleven years.
During this time, Latimer created patent drawings for
Alexander Graham Bell. He completed the drawings
and submitted them only hours before a competing
inventor. Bell was awarded the telephone patent in
1876 due to Latimer's hard work and drafting skills.
After Crosby and Gould, Latimer worked as a
draftsman at the Follandsbee Machine Shop. Here he
met Hiram Maxim and was hired to work at Maxim's
company, U.S. Electric Lighting. Maxim was an
inventor searching for ways to improve Thomas
Edison’s light bulb. Edison held the patent for the light
bulb, but the life span of the bulb was very short.
Maxim wanted to extend the life of the light bulb and
turned to Latimer for help.
Latimer taught himself the details of electricity. In
1881, he invented carbon filaments to replace paper
filaments in light bulbs. He then went on to improve
the manufacturing process for carbon filaments. Now
light bulbs lasted longer, were more affordable, and
had more uses. Latimer oversaw the installation of
electric street lights in North America and London. He
became chief electrical engineer for U.S. Electric
Lighting and supervised The Maxim-Westin Electric
Lighting Company in London.
Edison and beyond
In 1885, Thomas Edison hired Latimer to work in the
legal department of Edison Electric Light Company.
Latimer was the chief draftsman and patent authority
working to protect Edison's patents. He wrote the
widely acclaimed electrical engineering book called
Incandescent Electric Lighting: A Practical
Description of the Edison System. Latimer became one
of only 28 members of the “Edison Pioneers” and the
only African-American member. The Edison Pioneers
were the most highly regarded men in the electrical
field. Edison's company eventually became the
General Electric Company.
Latimer’s additional inventions included an early
version of the air conditioner; a locking rack for hats,
coats, and umbrellas; and a book support. He was also a
poet, musician, playwright, painter, civil rights activist,
husband, and father. Latimer died in 1928 at age 80.
Page 2 of 2
Reading reflection
21.2
1.
How did Lewis Latimer become a draftsman and electrical engineer?
2.
List Latimer's major inventions. What was his most important invention and why?
3.
Research: What is a “Renaissance man”? Why is Latimer referred to as a Renaissance man?
4.
Research: Latimer was an accomplished poet. Locate and identify the names of two of his poems.
5.
Research: When did the Edison Pioneers first meet? Locate an excerpt from the obituary published by the
Edison Pioneers honoring Lewis Latimer.
Name:
Date:
21.3 Electrical Power
21.3
How do you calculate electrical power?
In this skill sheet you will review the relationship between electrical power and Ohm’s law. As you work through
the problems, you will practice calculating the power used by common appliances in your home.
During everyday life we hear the word watt mentioned in reference to things like light bulbs and electric bills.
The watt is the unit that describes the rate at which energy is used by an electrical device. Energy is never created
or destroyed, so “used” means it is converted from electrical energy into another form such as light or heat. Since
energy is measured in joules, power is measured in joules per second. One joule per second is equal to one watt.
To calculate the electrical power “used” by an electrical component, multiply the voltage by the current.
Current x Voltage = Power, or P = IV
A kilowatt (kWh) is 1,000 watts or 1,000 joules of energy per second. On an electric bill you may have noticed
the term kilowatt-hour. A kilowatt-hour means that one kilowatt of power has been used for one hour. To
determine the kilowatt-hours of electricity used, multiply the number of kilowatts by the time in hours.
.
•
You use a 1,500-watt heater for 3 hours. How many kilowatt-hours of electricity did you use?
1 kilowatt
= 1.5 kilowatts
1,000 watts
1.5 kilowatts × 3 hours = 4.5 kilowatt-hours
1,500 watts ×
You used 4.5 kilowatt-hours of electricity.
1.
2.
3.
Your oven has a power rating of 5,000 watts.
a.
How many kilowatts is this?
b.
If the oven is used for 2 hours to bake cookies, how many kilowatt-hours (kWh) are used?
c.
If your town charges $0.15 per kWh, what is the cost to use the oven to bake the cookies?
You use a 1,200-watt hair dryer for 10 minutes each day.
a.
How many minutes do you use the hair dryer in a month? (Assume there are 30 days in the month.)
b.
How many hours do you use the hair dryer in a month?
c.
What is the power of the hair dryer in kilowatts?
d.
How many kilowatt-hours of electricity does the hair dryer use in a month?
e.
If your town charges $0.15 per kWh, what is the cost to use the hair dryer for a month?
Calculate the power rating of a home appliance (in kilowatts) that uses 8 amps of current when plugged into
a 120-volt outlet.
Page 2 of 2
4.
Calculate the power of a motor that draws a current of 2 amps when connected to a 12 volt battery.
5.
Your alarm clock is connected to a 120 volt circuit and draws 0.5 amps of current.
21.3
a.
Calculate the power of the alarm clock in watts.
b.
Convert the power to kilowatts.
c.
Calculate the number of kilowatt-hours of electricity used by the alarm clock if it is left on for one year.
d.
Calculate the cost of using the alarm clock for one year if your town charges $0.15 per kilowatt-hour.
6.
Using the formula for power, calculate the amount of current through a 75-watt light bulb that is connected
to a 120-volt circuit in your home.
7.
The following questions refer to the diagram.
a. What is the total voltage of the circuit?
b. What is the current in the circuit?
c. What is the power of the light bulb?
8.
9.
A toaster is plugged into a 120-volt household circuit. It draws 5 amps of
current.
a.
What is the resistance of the toaster?
b.
What is the power of the toaster in watts?
c.
What is the power in kilowatts?
A clothes dryer in a home has a power of 4,500 watts and runs on a special 220-volt household circuit.
a.
What is the current through the dryer?
b.
What is the resistance of the dryer?
c.
How many kilowatt-hours of electricity are used by the dryer if it is used for 4 hours in one week?
d.
How much does it cost to run the dryer for one year if it is used for 4 hours each week at a cost of $0.15
per kilowatt-hour?
10. A circuit contains a 12-volt battery and two 3-ohm bulbs in series.
a.
Calculate the total resistance of the circuit.
b.
Calculate the current in the circuit.
c.
Calculate the power of each bulb.
d.
Calculate the power supplied by the battery.
11. A circuit contains a 12-volt battery and two 3-ohm bulbs in parallel.
a.
What is the voltage across each branch?
b.
Calculate the current in each branch.
c.
Calculate the power of each bulb.
d.
Calculate the total current in the circuit.
e.
Calculate the power supplied by the battery.
Name:
Date:
21.3 Transformers
21.3
A transformer is a device used to change voltage and current. You may have
noticed the gray electrical boxes often located between two houses or
buildings. These boxes protect the transformers that “step down” high voltage
from power lines (13,800 volts) to standard household voltage (120 volts).
How a transformer works:
1.
The primary coil is connected to outside power lines. Current in
the primary coil creates a magnetic field through the secondary
coil.
2.
The current in the primary coil changes frequently because it is
alternating current.
3.
As the current changes, so does the strength and direction of the
magnetic field through the secondary coil.
4.
The changing magnetic field through the secondary coil induces
current in the secondary coil. The secondary coil is connected to
the wiring in your home.
Transformers work because the primary and secondary coils have different numbers of turns. If the secondary
coil has fewer turns, the induced voltage in the secondary coil is lower than the voltage applied to the primary
coil. You can use the proportion below to figure out how number of turns affects voltage:
Page 2 of 2
21.3
A transformer steps down the power line voltage (13,800 volts) to standard household voltage
(120 volts). If the primary coil has 5,750 turns, how many turns must the secondary coil have?
Solution:
V1 N1
=
V2 N2
13,800 volts 5750 turns
=
120 volts
N2
N 2 = 50 turns
1.
In England, standard household voltage is 240 volts. If you brought your own
hair dryer on a trip there, you would need a transformer to step down the voltage
before you plug in the appliance. If the transformer steps down voltage from 240
to 120 volts, and the primary coil has 50 turns, how many turns does the
secondary coil have?
2.
You are planning a trip to Singapore. Your travel agent gives you the proper
transformer to step down the voltage so you can use your electric appliances
there. Curious, you open the case and find that the primary coil has 46 turns and
the secondary has 24 turns. Assuming the output voltage is 120 volts, what is the
standard household voltage in Singapore?
3.
A businessman from Zimbabwe buys a transformer so that he can use his own electric appliances on a trip to
the United States. The input coil has 60 turns while the output coil has 110 turns. Assuming the input voltage
is 120 volts, what is the output voltage necessary for his appliances to work properly? (This is the standard
household output voltage in Zimbabwe.)
4.
A family from Finland, where standard household voltage is 220 volts, is planning a trip to Japan. The
transformer they need to use their appliances in Japan has an input coil with 250 turns and an output coil
with 550 turns. What is the standard household voltage in Japan?
5.
An engineer in India (standard household voltage = 220 volts) is designing a transformer for use on her
upcoming trip to Canada (standard household voltage = 120 volts). If her input coil has 240 turns, how many
turns should her output coil have?
6.
While in Canada, the engineer buys a new electric toothbrush. When she returns home she designs another
transformer so she can use the toothbrush in India. This transformer also has an input coil with 240 turns.
How many turns should the output coil have?
Name:
Date:
22.1 Magnetic Earth
22.1
Earth’s magnetic field is very weak compared with the strength of the field on the surface of the ceramic magnets
you probably have in your classroom. The gauss is a unit used to measure the strength of a magnetic field. A
small ceramic permanent magnet has a field of a few hundred up to 1,000 gauss at its surface. At Earth’s surface,
the magnetic field averages about 0.5 gauss. Of course, the field is much stronger nearer to the core of the planet.
1.
What is the source of Earth’s magnetic field according to what you have read in chapter 22?
2.
Today, Earth’s magnetic field is losing approximately 7 percent of its strength every 100 years. If the
strength of Earth’s magnetic field at its surface is 0.5 gauss today, what will it be 100 years from now?
3.
Describe what you think might happen if Earth’s magnetic field continues to lose strength.
4.
The graphic to the right illustrates one piece of evidence that proves the
reversal of Earth’s poles during the past millions of years. The ‘crust’ of
Earth is a layer of rock that covers Earth’s surface. There are two kinds of
crust—continental and oceanic. Oceanic crust is made continually (but
slowly) as magma from Earth’s interior erupts at the surface. Newly formed
crust is near the site of eruption and older crust is at a distance from the site.
Based on what you know about magnetism, why might oceanic crust rock
be a record of the reversal of Earth’s magnetic field? (HINT: What happens
to materials when they are exposed to a magnetic field?)
5.
The terms magnetic south pole and geographic north pole refer to locations
on Earth. If you think of Earth as a giant bar magnet, the magnetic south
pole is the point on Earth’s surface above the south end of the magnet. The
geographic north pole is the point where Earth’s axis of rotation intersects
its surface in the northern hemisphere. Explain these terms by answering the
following questions.
6.
a.
Are the locations of the magnetic south pole and the geographic north
pole near Antarctica or the Arctic?
b.
How far is the magnetic south pole from the geographic north pole?
c.
In your own words, define the difference between the magnetic south pole and the geographic north
pole.
A compass is a magnet and Earth is a magnet. How does the magnetism of a compass work with the
magnetism of Earth so that a compass is a useful tool for navigating?
Page 2 of 2
7.
The directions—north, east, south, and west—are arranged on a compass so that they align with
360 degrees. This means that zero degrees (0°) and 360° both represent north. For each of the
following directions by degrees, write down the direction in words. The first one is done for you.
a.
45° Answer: The direction is northeast.
b.
180°
c.
270°
d.
90°
e.
135°
f.
315°
22.1
Magnetic declination
Earth’s geographic north pole (true north) and magnetic south pole are located near each other, but they are not at
the same exact location. Because a compass needle is attracted to the magnetic south pole, it points slightly east
or west of true north. The angle between the direction a compass points and the direction of the geographic north
pole is called magnetic declination. Magnetic declination is measured in degrees and is indicated on
topographical maps.
8.
Let’s say you were hiking in the woods and relying on a map and compass to navigate. What would happen
if you didn’t correct your compass for magnetic declination?
9.
Are there places on Earth where magnetic declination equals 0°? Use the Internet or your local library to find
out where on Earth there is no magnetic declination.
Name:
Date:
22.3 Michael Faraday
22.3
Despite little formal schooling, Michael Faraday rose to become one of England’s top research
scientists of the nineteenth century. He is best known for his discovery of electromagnetic induction, which made
possible the large-scale production of electricity in power plants.
Reading his way to a job
Michael Faraday was born
on September 22, 1791, in
Surrey, England, the son of
a blacksmith. His family
moved to London, where
Michael received a
rudimentary education at a
local school.
At 14, he was apprenticed
to a bookbinder. He enjoyed
reading the materials he
was asked to bind, and found himself mesmerized by
scientific papers that outlined new discoveries.
A wealthy client of the bookbinder noticed this
voracious reader and gave him tickets to hear
Humphry Davy, the British chemist who had
discovered potassium and sodium, give a series of
lectures to the public.
Faraday took detailed notes at each lecture. He bound
the notes and sent them to Davy, asking him for a job.
In 1812, Davy hired him as a chemistry laboratory
assistant at the Royal Institution, London’s top
scientific research facility.
Despite his lack of formal training in science or math,
Faraday was an able assistant and soon began
independent research in his spare time. In the early
1820s, he discovered how to liquefy chlorine and
became the first to isolate benzene, an organic solvent
with many commercial uses.
The first electric motor
Faraday also was interested in electricity and
magnetism. After reading about the work of Hans
Christian Oersted, the Danish physicist, chemist, and
electromagnetist, he repeated Oersted’s experiments
and used what he learned to build a machine that used
an electromagnet to cause rotation—the first electric
motor.
Next, he tried to do the opposite, to use a moving
magnet to cause an electric current. In 1831, he
succeeded. Faraday’s discovery is called
electromagnetic induction, and it is used by power
plants to generate electricity even today.
The Faraday effect
Faraday first developed the concept of a field to
describe magnetic and electric forces, and used iron
filings to demonstrate magnetic field lines. He also
conducted important research in electrolysis and
invented a voltmeter.
Faraday was interested in finding a connection
between magnetism and light. In 1845 he discovered
that a strong magnetic field could rotate the plane of
polarized light. Today this is known as the Faraday
effect.
A scientist’s public education
Faraday was a teacher as well as a researcher. When
he became director of the Royal Institution laboratory
in 1825, he instituted a popular series of Friday
Evening Discourses. Here paying guests (including
Prince Albert, who was Queen Victoria’s husband)
were entertained with demonstrations of the latest
discoveries in science.
A series of lectures on the chemistry and physics of
flames, titled “The Natural History of a Candle,” was
among the original Christmas Lectures for Children,
which continue to this day.
Named in his honor
Faraday continued his work at the Royal Institution
until just a few years before his death in 1867. Two
units of measure have been named in his honor: the
farad, a unit of capacitance, and the faraday, a unit of
charge.
Page 2 of 2
Reading reflection
22.3
1.
What did Michael Faraday do to get a job with Humphry Davy? Why was this effort important in
getting Faraday started in science?
2.
Research benzene and list two modern-day commercial uses for this chemical.
3.
Based on the reading, define electromagnetic induction.
4.
In your own words, describe the Faraday effect. In your description, explain the term “polarized light.”
5.
How did Faraday contribute to society during his time as the director of the Royal Institution laboratory?
6.
Name two ways in which Faraday’s work affects your own life in the twenty-first century.
7.
Imagine you could go back in time to see one of Faraday’s demonstrations. Explain why you would like to
attend one of his demonstrations.
8.
Activity: Use iron filings and a magnet to demonstrate magnetic field lines, or prepare a simple
demonstration of electromagnetic induction for your classmates.
Name:
Date:
22.3 Model Maglev Train Project
22.3
Magnetically levitating (Maglev) trains use electromagnetic force to lift the
train above the tracks. This system greatly reduces wear because there are few
moving parts that carry heavy loads. It’s also more fuel efficient, since the
energy needed to overcome friction is greatly reduced. Although maglev
technology is still in its experimental stages, many engineers believe it will
become the standard for mass transit systems over the next 100 years.
This project will give you an opportunity to create a model maglev train. You
can even experiment with different means of providing power to your train.
Materials
•
•
•
•
•
•
52 one-inch square magnets with north and south poles on the faces, rather than ends (found at hobby shops)
One strip of 1/4-inch thick foam core, 24 inches long by 4 inches wide
Two strips of 1/4-inch thick foam core, 24 inches long by 2.5 inches wide
One strip of 1/4-inch thick foam core, 6 inches long by 3.75 inches wide
Hot melt glue and glue gun
Masking tape
Directions
1.
Cut a strip of masking tape 24 inches long. Press a line of 24 magnets onto the tape, north sides up.
2.
Hold an additional magnet north side down and run it along the strip to make sure that the entire “track” will
repel the magnet. Flip over any magnets that attract your test magnet.
3.
Glue the magnet strip along one long side of the 24-by-4-inch foam core rectangle.
4.
Repeat steps 1-2, then glue the
second magnet strip along the
opposite side to create the other
track.
5.
Place a bead of hot glue along the
cut edge and attach one 24-by-2.5
inch foam core rectangle to form a
short wall.
Page 2 of 2
6.
Repeat step 5 to form the opposite wall. This keeps the train from sliding sideways off the track.
22.3
7.
To create your train, glue the south side of a magnet to each corner of the small foam core rectangle.
8.
Turn the train over so that the north side of its magnets face the tracks. Place your train above the track and
watch what happens!
Extensions:
1.
Experiment with various means to propel your train along the tracks. Consider using balloons, rubber bands
and toy propellers, small motors (available at hobby stores) or even jet propulsion using vinegar and baking
soda as fuel.
2.
Build a longer, more permanent track using plywood shelving. Use clear, flexible plastic for the front wall so
that you can see the train floating above the track.
3.
Find out how much weight your train can carry. Are some propulsion systems able to carry more weight than
others? Why?
4.
Have a design contest to see who can build the fastest train, or the train that can carry the most weight from
one end of the track to the other.