circuits and circuit elementssection 1 © houghton mifflin harcourt publishing company preview...

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



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.



What do you think?

1

2

3

4

5

6

7

8



Click below to watch the Visual Concept.

Schematic Diagram and Common Symbols

Visual Concept



Schematic Diagrams

• Schematic diagrams use symbols to represent components.

• They show how the parts in an electrical device are arranged.



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



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).



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.



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.




Visual Concept

Internal Resistance, EMF, and Terminal Voltage



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



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



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.



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.



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.



Resistors in Series Vbattery= V1 + V2

– Conservation of energy

Vbattery= IR1 + IR2

– Ohm’s law

Vbattery= I(R1 + R2)

Vbattery= IRequivalent

• Requivalent = R1 + R2



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.



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



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.



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



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.



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




Visual Concept

Comparing Resistors in Series and in Parallel



Summary



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?




• 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.



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



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?




Visual Concept

Analysis of Complex Circuits



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:



• 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.




• 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




• 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




• 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 elementssection 1 © houghton mifflin harcourt publishing company preview...

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