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Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Preview
Section 1 Schematic Diagrams and Circuits
Section 2 Resistors in Series or in Parallel
Section 3 Complex Resistor Combination
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
What do you think?
• Scientists often use symbols to represent electrical components, such as batteries, bulbs, and wires. On the next slide, you will see the symbols for eight common electrical components that you have seen and discussed previously. • Predict the component shown by looking at each
symbol. • Briefly explain why you think each symbol represents
that particular electrical component.
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
What do you think?
1
2
3
4
5
6
7
8
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Click below to watch the Visual Concept.
Schematic Diagram and Common Symbols
Visual Concept
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Schematic Diagrams
• Schematic diagrams use symbols to represent components.
• They show how the parts in an electrical device are arranged.
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Electric Circuits
• An electric circuit is a set of components providing a complete, closed-loop path for the movement of electrons.– Called a closed circuit
• If the path is broken, the electrons do not flow.– Called an open circuit
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Inside a Light bulb
• A complete conducting path is established inside the light bulb.– The tip of the bulb (a) is
connected to one side of the filament (see the black line).
– The threads on the side of the bulb (c) are connected to the other side of the filament (see the white line).
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Short Circuits
• A short circuit bypasses the light bulb or other load.– It is a closed circuit.– Electrons flow directly from - to + without passing
through the bulb.– The current is large and the wire becomes hot.
• Short circuits in homes can cause fires.
– Fuses or circuit breakers are designed to turn off the electron flow if short circuits occur.
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Potential Difference in Circuits
• A device that increases the PE of the electrons, such as a battery, is a source of emf (electromotive force).– Not really a force, but a PE difference
• Energy is conserved in electric circuits.– The potential difference (V) for the battery equals
the energy converted into heat as the electrons move through the bulb.
• Electrons gain energy (battery) and lose energy (bulb) as they make a complete trip.
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Click below to watch the Visual Concept.
Visual Concept
Internal Resistance, EMF, and Terminal Voltage
Circuits and Circuit Elements Section 1
© Houghton Mifflin Harcourt Publishing Company
Now what do you think?
• Draw schematic diagrams showing each of the following circuits:• An open circuit including a battery, open switch, and
bulb• A closed circuit including a battery, closed switch, and
resistor• A short circuit including a battery, bulb, and closed
switch
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
The student is expected to:TEKS
5F design, construct, and calculate in terms of
current through, potential difference across,
resistance of, and power used by electric circuit
elements connected in both series and parallel
combinations
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
What do you think?
• Figure (a) shows a single bulb and battery as seen before. Figures (b) and (c) each show two bulbs connected to the battery. The batteries and bulbs are all identical. Answer the three questions on the next slide and explain your reasoning.
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
What do you think?
• How will the brightness of (b) and (c) compare to each other and how does each compare to (a)? Explain.
• How will the brightness of (d) and (e) compare to each other and how does each compare to (a)? Explain.
• Compare the total current leaving the battery in each of the three circuits. Explain.
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Resistors in Series
• Series describes components of a circuit that provide a single path for the current.– The same electrons must pass through both light bulbs so the
current in each is the same.
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Resistors in Series Vbattery= V1 + V2
– Conservation of energy
Vbattery= IR1 + IR2
– Ohm’s law
Vbattery= I(R1 + R2)
Vbattery= IRequivalent
• Requivalent = R1 + R2
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Equivalent Resistance
• Solving problems with series resistors:– Find the equivalent resistance.
– Use Req with Ohm’s law to find V or I.
– Use I and R1, R2, etc. to find V1, V2, etc.
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Classroom Practice Problems• A 6.00 V lantern battery is connected to each of
the following bulb combinations. Find the current in each circuit and the potential difference across each bulb.– One bulb with a resistance of 7.50 – Two bulbs in series, each with a resistance of 7.50 – Four bulbs in series, each with a resistance of 7.50
• Answers: – 0.800 A, 6.00 V– 0.400 A, 3.00 V each– 0.200 A, 1.50 V each
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Resistors in Parallel
• Parallel describes components providing separate conducting paths with common connecting points.– The potential difference is the same for parallel components.– Electrons lose the same amount of energy with either path.
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Resistors in Parallel• Ibattery = I1 + I2
– Conservation of charge
•
– Ohm’s law
Vbattery= V1 = V2– Potential energy loss is the same across all parallel resistors.
• Because Vbattery= V1 = V2, the equation above reduces as follows:
1 2
1 2
battery
eq
V V V
R R R
1 2
11 1
eqR R R
1 2eq
V VV
VR VR VR
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Equivalent Resistance
• Solving problems with parallel resistors:– Find the equivalent resistance.
– Use Req with Ohm’s law to find V or Itotal.
– Use V to find I1, I2, etc.
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Classroom Practice Problems• Find the equivalent resistance, the total current
drawn by the circuit, and the current in each resistor for a 9.00 V battery connected to:– One 30.0 resistor– Three 30.0 resistors connected in parallel
• Answers:– 30.0 , 0.300 A, 0.300 A– 10.0 , 0.900 A, 0.300 A
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Click below to watch the Visual Concept.
Visual Concept
Comparing Resistors in Series and in Parallel
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Summary
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Wiring Lights
• The series circuit shows a bulb burned out.– What will happen to the
other bulbs?– Would this also happen in
the parallel circuit?
• Assuming the bulbs are identical:– Which circuit will draw more
current?– In which circuit are the
bulbs brighter?
Circuits and Circuit Elements Section 2
© Houghton Mifflin Harcourt Publishing Company
Now what do you think?
• How will the brightness of (b) and (c) compare to each other and how does each compare to (a)? Explain.
• How will the brightness of (d) and (e) compare to each other and how does each compare to (a)? Explain.
• Compare the total current leaving the battery in each of the three circuits. Explain.
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
The student is expected to:TEKS
5F design, construct, and calculate in terms of
current through, potential difference across,
resistance of, and power used by electric circuit
elements connected in both series and parallel
combinations
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
What do you think?
• Household circuits typically have many outlets and permanent fixtures such as hanging light fixtures on each circuit. • Are these wired in series or in parallel?• Why do you believe one of these methods has an
advantage over the other method?• What disadvantages would the other method of wiring
have for household circuits?
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
Click below to watch the Visual Concept.
Visual Concept
Analysis of Complex Circuits
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
Complex Resistor Calculations
• Req for 6.0 and 2.0 – Answer: 8.0
• Req for 8.0 and 4.0 – Answer: 2.7
• Req for 3.0 and 6.0 and 2.7 and 1.0 – Answer: 12.7
• So, the resistance of all 6 resistors is equivalent to a single 12.7 resistor.
• To find the equivalent resistance for the circuit shown above, follow the steps shown to the right:
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
• Find the total current in the equivalent circuit.– Answer: 0.71 A– This is the current through
the 1.0 , 6.0 (on the left), and 3.0 loads
• Find the total potential drop across the parallel combination of three resistors.– Answer: 1.9 V– Continued on the next slide
• For the 2.0 resistor, find the current and the potential difference.– To solve this problem, use
the step-by-step approach shown.
Complex Resistor Calculations
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
• Find the current through the combined 6.0 and 2.0 resistor.– Answer: 0.24 A
• Find the potential difference across the 2.0 resistor.– Answer: 0.48 V
Complex Resistor Calculations
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
• For the circuit shown, find the:– Equivalent resistance– Current through the 3.0
resistor– Potential difference across
the 6.0 resistor
• Answers:– 6.6 , 1.8 A, 6.5 V
Classroom Practice Problems
Circuits and Circuit Elements Section 3
© Houghton Mifflin Harcourt Publishing Company
Now what do you think?
• Household circuits typically have many outlets and permanent fixtures such as hanging light fixtures on each circuit. • Are these wired in series or in parallel?• Why do you believe one of these methods has an
advantage over the other method?• What disadvantages would the other method of wiring
have for household circuits?