Electric Circuits Vocabulary · The electric power in watts (W) is associated with a complete electric circuit. A circuit component represents the rate at which energy is converted

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Electric Circuits Vocabulary

Term Definition

Electric Current

Electric Circuit

Open Circuit

Conductors

Insulators

Ohm’s Law • Current

• Voltage

• Resistance

Electrical Power

Series Circuit

Parallel Circuit

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Activity – And Then There Was Light!

Focus Question: What are the essential components and configurations needed to make a bulb light? Equipment: One cell, one bulb, one wire. Directions: Make the bulb light using only the given equipment. Draw each successful circuit you create.

There is more than one configuration that will be successful. You need to have at least two.

Once you identified a successful configuration, you also need to trace the closed loop path

around the circuit.

Unsuccessful attempts (2) Successful attempts (at least 2)

Conclusion: Consensus:

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Symbols Used in Basic Circuits

Sketch a circuit with 2 resistors, a light bulb and a single cell battery. Sketch a circuit with 3 light bulbs, an open switch, and a single cell battery.

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Draw three 10 Ω resistors connected in series to a 6 volt battery: To determine the total resistance in a series circuit you add:

Rtotal = R1 + R2 + R3 + . . . Thus the total resistance of a circuit that has a 2 Ω , 4 Ω and 10 Ω resistor is:

Rtotal = 2 + 4 + 10

Rtotal = 16 Ω

Main Ideas

Current Voltage Total Resistance Adding a bulb

Series Circuits

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Determine the total resistance in each circuit below.

1.

Rtotal =

2.

Rtotal =

3.

Rtotal =

4. Rtotal =

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Information: Resistance and Ohm’s Law The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it:

V = IR Triangle:

If the resistance is constant over a considerable range of voltage, then Ohm's law, V = IR, can be used to predict the behavior of the material.

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Problem Solving Steps: 1. Write down givens and unknown. 2. Write down equation. 3. Plug in variables. 4. Solve for unknown.

Don’t forget proper units!!!! Example #1: If the Current= 2A and the Resistance = 500Ω, then determine the voltage.

Looking For Given Relationship Solution

Example #2: If the voltage in a circuit is 160 V, and the current is 4A, then what is the resistance of the circuit?


Example #3: A 140 Volts is applied to a 200 Ohm resistor. How much current passes through the resistor?


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Classwork Practice Problems 1. A light bulb is plugged into a wall outlet (120 V). It uses 16 A. What is the light bulbs

resistance? Looking For Given Relationship Solution

2. A flash light bulb is labeled to uses 1.77 A. Its resistance is 3.20 Ω. What voltage is the light bulb rated for?


3. A stereo speaker has a resistance of 16.00 Ω. When it is operating at full power (exactly 200 watts) it uses 50 volts of electricity. What is the current drawn by the speaker?


4. A toaster plugged into the wall, (120 volts), uses 24 amps of electricity. What is the resistance of the toaster?


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5. A light bulb is plugged into a wall outlet (220 V). It uses 0.68 A. What is the light bulbs resistance?


6. A flash light bulb is labeled to uses 1.77 A. Its resistance is 1.60 Ω. What voltage is the light

bulb rated for? Looking For Given Relationship Solution

7. Another flash light bulb is rated to use 0.300 A and has a resistance of 4.0 Ω. How much voltage does this bulb use?


8. A stereo speaker has a resistance of 8.00 Ω. When it is operating at full power (exactly100 watts) it uses 35 volts of electricity. What is the current drawn by the speaker?


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Ohm’s Law Homework Problems

9. A toaster plugged into the wall, (120 volts), uses 14 amps of electricity. What is the resistance of the toaster?


10. A motor in a radio control car uses 7.2 volts and draws 14.4 amps of electricity. What is the resistance of the motor?


11. The resistance of dry human skin is about 500,000 Ω and wet, sweaty, human skin is about 1000 Ω. How much current passes across someone’s fingers if they touch the leads of a 9 volt battery when their skin is wet or dry? Wet Skin


Dry Skin Looking For Given Relationship Solution

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Information: Power The electric power in watts (W) is associated with a complete electric circuit. A circuit component represents the rate at which energy is converted from the electrical energy of the moving charges to some other form, e.g., heat, mechanical energy, or energy stored in electric fields or magnetic fields. For a resistor in a circuit the power is given by the product of applied voltage and the electric current:

𝑃 = 𝑉2

𝑅 or 𝑃 = 𝐼2𝑅 or 𝑃 = 𝐼𝑉 Triangle:

Classwork Practice Problems

1. Find the current drawn from a 1200 W hair dryer connected to a 120 V source. Find the resistance of the hair dryer.


2. A car lighter has a resistance of 4 Ω. If it draws from a 12 V battery, what is the power dissipated?


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Series Circuit Worksheet

Be sure to NEATLY draw the circuit for each problem and fill in the table. Show your work!! Use the sample

layout below.

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1. A series circuit contains a 12-V battery and three bulbs with a resistance of 4 Ω, 6 Ω, and 8 Ω.

Fill in the values in the circuit diagram below. What is the total resistance in the circuit? What

is the voltage drop of each bulb? What is the current that each bulb uses? What is the power in

each bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1 4 Ω

Bulb 2 6 Ω

Bulb 3 8 Ω

Total 12 V

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2. A series circuit contains a 120-V battery and three bulbs with a resistance of 12 Ω, 20 Ω, and

60 Ω. Fill in the values in the circuit diagram below. What is the total resistance in the circuit?

What is the voltage drop of each bulb? What is the current that each bulb uses? What is the

power in each bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

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each bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

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Series Circuits - Homework




each bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

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each bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

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Draw three 10 Ω resistors connected in parallel:

Main Ideas

Current Voltage Total Resistance Adding a bulb

Parallel Circuits

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Parallel Circuit Worksheet Be sure to NEATLY draw the circuit for each problem and fill in the table. Show your work!! Use the sample layout below.

1. A parallel circuit contains a 12-V battery and three bulbs with a resistance of 4 Ω, 6 Ω, and 8 Ω.

Fill the values in on the circuit diagram. What is the total resistance in the circuit? What is the

voltage drop of each bulb? What is the current that each bulb uses? What is the power in each

bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

VT =______ RT =______ IT = ______

R2 = ____ V2 = ____ I2 = ____

R1 = ____ V1 = ____ I1 = ____

R3 = V3 = ____ I3 = ____

R1 R2

R3

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2. A parallel circuit contains a 120-V battery and three bulbs with a resistance of 20 Ω, 30 Ω, and

60 Ω. Fill the values in on the circuit diagram. What is the total resistance in the circuit? What


each bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

VT =______ RT =______ IT = ______

R2 = ____ V2 = ____ I2 = ____

R1 = ____ V1 = ____ I1 = ____

R3 = V3 = ____ I3 = ____

R1 R2

R3

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bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

VT =______ RT =______ IT = ______

R2 = ____ V2 = ____ I2 = ____

R1 = ____ V1 = ____ I1 = ____

R3 = V3 = ____ I3 = ____

R1 R2

R3

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Parallel Circuit Homework




bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

VT =______ RT =______ IT = ______

R2 = ____ V2 = ____ I2 = ____

R1 = ____ V1 = ____ I1 = ____

R3 = V3 = ____ I3 = ____

R1 R2

R3

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2. A parallel circuit contains a 60-V battery and three bulbs with a resistance of 5 Ω, 10 Ω, and

15 Ω. Fill the values in on the circuit diagram. What is the total resistance in the circuit? What


each bulb?

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Power

(Watts)

Bulb 1

Bulb 2

Bulb 3

Total

VT =______ RT =______ IT = ______

R2 = ____ V2 = ____ I2 = ____

R1 = ____ V1 = ____ I1 = ____

R3 = V3 = ____ I3 = ____

R1 R2

R3

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Summary Information: Series and Parallel A _____________ (Figure 1) is a circuit in which resistors are arranged in a chain, so the current has only one path to take. The current is the _______ through each resistor. The total resistance of the circuit is found by simply adding up the resistance values of the individual resistors:

RT = R1 + R2 + R3 + ... A _____________________ (Figure 2 & 3) is a circuit in which the resistors are arranged with their heads connected together, and their tails connected together [Figures 2 and 3]. The current in a parallel circuit breaks up, with some flowing along each parallel branch and re-combining when the branches meet again. The _____________ across each resistor in parallel is the same. The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total:

1/RT = 1/R1 + 1/R2 + 1/R3 +...

Figure 1 Resistors connected in series.

Figure 2 Example of a circuit

containing three resistors connected in parallel

Figure3 Circuit containing

resistors in parallel, equivalent to Figure 2

If you add a resistor in: Series Parallel equivalent resistance increases Decreases total current in circuit decreases Increases current through each device the same depends on its resistance voltage across each device depends on its resistance the same

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Critical Thinking Questions 1. To connect a pair of resistors so that your combined resistance would increase they should be

connected how? To see the resistance decrease they should be connected how?

2. Why is there a difference in total resistance if you connect three 60 Ω resistors in series versus three 60 Ω resistors in parallel?

3. Find the combined resistance of a 12, 4 and 6 Ω resistors connected to a 12-volt battery in series and then again in parallel.

4. Why do Christmas lights turn off if one light bulb is bad? How are they wired?

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The Tollway Analogy The flow of charge through the wires of a circuit can be compared to the flow of cars along a toll way system in a very crowded metropolitan area. The main source of resistance on a toll way system are the tollbooths. Stopping cars and forcing them to pay a toll at a tollbooth not only slows the cars down, but in a highly trafficked area, will also cause a bottleneck with a backup for miles. The rate at which cars flow past a point on that toll way system is reduced significantly by the presence of a tollbooth. Clearly, tollbooths are the main resistor to car flow.

This can also be related to thinking about walking through the hallways at school. If there were multiple

pathways to walk down, then it would be much easier to walk to the front office. If the class were

restricted to only one hallway for the trip, then it would take longer and would be more crowded with

people pushing their way through.

Come up with your own scenario that shows a relationship between multiple paths compared to one in

order to explain series vs. parallel circuits.

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Resistivity The resistance of a wire is proportional to the length of the wire and inversely proportional to the thickness of the wire. The temperature and the material of the wire will also play a role in how fast or slow a current can flow.

R = Resistance ρ = Resistivity l = length of wire A = Area of wire You can think of how resistance changes within a circuit, and relate it to how people travel through hallways.

• A Thick Wire (large cross-sectional area) is similar to a wide hallway, while a thin wire would be a smaller hallway. Humans would rather walk down the wide hallway because travel is easier, similar to how current travels down the path with least resistance.

• A Long Wire would be similar to a long hallway to walk down, while a short wire would be like a short hallway. Humans would rather walk down the shorter hallway because they are able to reach their destination quicker and easier.

• A Hot Wire would be similar to a hallway on a summer day with excited students moving about, while a cold hallway would be found in the winter time with students sitting bundled up and not moving around much. If a person walked down the hot hallway, they would have more people in their way to say “Hi” to, causing them to take longer to make it through the hallway.

Critical Thinking Questions

1. Why are thick wires rather than thin wires usually used to carry large current?

2. Could the same length of a copper and aluminum wire have the same resistance? Explain.

3. Compare the Resistances of the following: a. Thick Wire vs. Thin Wire

b. Long Wire vs. Short Wire

c. Hot Wire vs. Cool Wire

d. Series Circuit vs. Parallel Circuit

Note: This equation is just for background information and is not necessary for you to know.

Al

Rρ

=

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Mythbusters: https://district158.haikulearning.com/ewagner/honorsphysics/cms_page/view/5296294

https://district158.haikulearning.com/ewagner/honorsphysics/cms_page/view/5296294

Electric Circuits Vocabulary · The electric power in watts (W) is associated with a complete electric circuit. A circuit component represents the rate at which energy is converted

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