Transcript Chapter 16 - Ms

Chapter 16
Section 3 Circuits
Objectives
• Use schematic diagrams to represent circuits.
• Distinguish between series and parallel circuits.
• Calculate electric power using voltage and current.
• Explain how fuses and circuit breakers are used to
prevent circuit overload.
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Chapter 16
Section 3 Circuits
Bellringer
1. Inexpensive electrical power is essential. List at least ten
electrical devices that you have used today.
2. In some strings of Christmas lights, none of the lights work
if one light is burned out. What is a possible explanation
for this?
3. A big feast is being prepared for several people in a home.
The cooks are using a turkey roaster, the oven, an electric
mixer, the blender, and the toaster. Every light is on and so
is the refrigerator. All at once the power in the kitchen goes
out. What is an explanation for this, and how can it be
corrected?
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Chapter 16
Section 3 Circuits
What Are Circuits?
• An electric circuit is a path through which charges
can be conducted.
• An electric circuit is a set of electrical
components connected such that they provide one
or more complete paths for the movement of
charges.
• The conducting path produced when a light bulb is
connected across the battery’s terminals is called a
closed circuit.
• Without a complete path, there is no charge flow and
therefore no current. This is called an open circuit.
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Chapter 16
Section 3 Circuits
Electric Circuit
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Chapter 16
Section 3 Circuits
What Are Circuits?, continued
• Switches interrupt the flow of charges in a circuit.
• You can use a switch to open and close a circuit.
• Schematic diagrams are used to represent circuits.
• A schematic diagram is a graphical representation
of a circuit that uses lines to represent wires and
different symbols to represent components.
• Each element used in a piece of electrical
equipment is represented by a symbol that reflects
the element’s construction or function.
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Chapter 16
Section 3 Circuits
Series and Parallel Circuits
• Series circuits have a single path for current.
• When appliances or other devices are connected
in a series circuit, they form a single pathway for
charges to flow.
• In a series circuit, the components of a circuit form
a single path for current.
• The current in each device is the same.
• The resistances may be different.
• The voltage across each device in a series circuit can be
different.
• If one element along the path in a series circuit is
removed, the circuit will not work.
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Chapter 16
Section 3 Circuits
Series and Parallel Circuits, continued
• Parallel circuits have multiple paths for current.
• A parallel circuit is a circuit in which all of the
components are connected to each other side by
side.
• The voltage across each device is the same.
• The current in each device does not have to be
the same.
• A break in any one path in a parallel circuit does
not interrupt the flow of electric charge in the other
paths.
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Chapter 16
Section 3 Circuits
Series and Parallel
When bulbs are connected in
series, charges must pass
through both light bulbs to
complete the circuit.
When devices are connected in
parallel, charges have more than
one path to follow. The circuit can
be complete even if one light
bulb burns out.
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Chapter 16
Section 3 Circuits
Electric Power and Electrical Energy
• Electrical energy is the energy that is associated
with charged particles because of their positions.
• Electric power is the rate at which electrical energy is
used in a circuit.
• The rate at which electrical work is done is called
electric power.
power  current  voltage
P = IV
• The SI unit for power is the watt (W).
• 1W=1A1V
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Chapter 16
Section 3 Circuits
Electric Power and Electrical Energy, continued
• If you combine the electric power equation above
with the equation V = IR, the power lost, or
dissipated, by a resistor can be calculated.
2
V
P = I 2R =
R
• Electric companies measure energy consumed in
kilowatt-hours.
• 1 kW•h = 3.6  106 J.
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Chapter 16
Section 3 Circuits
Equation for Electric Power
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Chapter 16
Section 3 Circuits
Math Skills
•
Electric Power When a hair dryer is plugged into a
120 V outlet, it has a 9.1 A current in it. What is the
hair dryer’s power rating?
1. List the given and unknown values.
Given:
voltage, V = 120 V
current, I = 9.1 A
Unknown: electric power, P = ? W
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Chapter 16
Section 3 Circuits
Math Skills, continued
2. Write the equation for electric power.
power = current × voltage
P = IV
3. Insert the known values into the equation, and
solve.
P = (9.1 A)(120 V)
P = 1.1 × 103 W
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Chapter 16
Section 3 Circuits
Fuses and Circuit Breakers
• When electrical wires carry more than a safe level of
current, the circuit is said to be overloaded.
• A short circuit can happen if a wire’s insulation wears
down, two wires may touch, creating an alternative
pathway for current.
• Fuses melt to prevent circuit overloads.
• A fuse an electrical device that contains a metal
strip that melts when current in the circuit
becomes too great.
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Chapter 16
Section 3 Circuits
Fuses and Circuit Breakers
• Circuit breakers open circuits with high current.
• A circuit breaker a switch that opens a circuit
automatically when the current exceeds a certain
value.
• The circuit breaker acts as a switch.
• Unlike fuses, circuit breakers can be reset by
turning the switch back on.
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Chapter 16
Section 3 Circuits
Concept Mapping
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Chapter 16
Standardized Test Prep
Understanding Concepts
1. A 12-volt battery is connected to a light bulb that has
a resistance of 240 ohms. Calculate the amount of
current in amperes drawn by the circuit.
A. 0.05 A
B. 0.5 A
C. 2.0 A
D. 20.0 A
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Chapter 16
Standardized Test Prep
Understanding Concepts, continued
1. A 12-volt battery is connected to a light bulb that has
a resistance of 240 ohms. Calculate the amount of
current in amperes drawn by the circuit.
A. 0.05 A
B. 0.5 A
C. 2.0 A
D. 20.0 A
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Standardized Test Prep
Understanding Concepts, continued
2. Which of the following statements is true?
F. Electrical forces exist between any two neutral
particles.
G. Electrical forces exist between any two charged
particles.
H. Electrical forces exist only between particles with
the same charge.
I. Electrical forces exist only between particles with
opposite charges.
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Standardized Test Prep
Understanding Concepts, continued
2. Which of the following statements is true?
F. Electrical forces exist between any two neutral
particles.
G. Electrical forces exist between any two charged
particles.
H. Electrical forces exist only between particles with
the same charge.
I. Electrical forces exist only between particles with
opposite charges.
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Understanding Concepts, continued
3. What happens to an object that is charged by
induction?
A. It acquires excess electrons.
B. It remains electrically neutral.
C. It acquires a net charge from the object that is
inducing the charge.
D. A current exists between it and the object that is
inducing the charge.
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Understanding Concepts, continued
3. What happens to an object that is charged by
induction?
A. It acquires excess electrons.
B. It remains electrically neutral.
C. It acquires a net charge from the object that is
inducing the charge.
D. A current exists between it and the object that is
inducing the charge.
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Understanding Concepts, continued
4. A stream of water is deflected when a negatively
charged rod is held close to it. Use the concept of
induced charge to explain what happens.
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Standardized Test Prep
Understanding Concepts, continued
4. A stream of water is deflected when a negatively
charged rod is held close to it. Use the concept of
induced charge to explain what happens.
Answer: A charge is induced on the water by the
charged rod. Attraction between the charged part of
the stream and the rod deflects the flow.
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Understanding Concepts, continued
5. How does a fuse protect a circuit from overloading?
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Chapter 16
Standardized Test Prep
Understanding Concepts, continued
5. How does a fuse protect a circuit from overloading?
Answer: The fuse has a thin wire with a low melting
point. When electrical resistance increases the
temperature too high, it melts and breaks the circuit.
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Reading Skills
In 1909 Robert Millikan measured the charge on an
electron in what is known as the oil-drop experiment.
He sprayed oil droplets into a chamber. Two plates
with opposite charges produced an electric field.
Some of the drops acquired a negative charge. The
field was adjusted so there was an upward force
equal to the downward pull of gravity. From the
strength of this force, Millikan could calculate the
amount of the electric charge on the drop.
6. Analyze how the electric field could cause an oil
drop to float inside the chamber.
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Standardized Test Prep
Reading Skills, continued
6. Analyze how the electric field could cause an oil
drop to float inside the chamber.
Answer: Electrical forces between the charged particle
an the charged plates balance the downward pull of
gravity.
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Chapter 16
Standardized Test Prep
Interpreting Graphics
7. Which metal would be the
best choice for a power
line, based on electrical
resistance?
F. aluminum
G. iron
H. lead
I. silver
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Chapter 16
Standardized Test Prep
Interpreting Graphics
7. Which metal would be the
best choice for a power
line, based on electrical
resistance?
F. aluminum
G. iron
H. lead
I. silver
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Chapter 16
Standardized Test Prep
Interpreting Graphics
8. Which metal would most
likely be then best
substitute for the tungsten
filament in an incandescent
light bulb based on
resistance?
A. aluminum
B. iron
C. lead
D. silver
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Chapter 16
Standardized Test Prep
Interpreting Graphics
8. Which metal would most
likely be then best
substitute for the tungsten
filament in an incandescent
light bulb based on
resistance?
A. aluminum
B. iron
C. lead
D. silver
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