Circuits

Circuits

Middle School

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Learning Objectives

• Define an electric circuit and name its essential parts.

• Compare the differences and similarities between series and parallel circuits.

• Explain Ohm's Law and the relationship between voltage, current, and resistance.

• Describe how energy changes and is conserved in an electric circuit.

• Learn how to calculate total resistance in series and parallel circuits.

Key Vocabulary

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Circuit

A closed loop path through which an electric current is able to flow continuously.

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Current

The steady flow of electric charges, usually electrons, through a conducting material like a wire.

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Voltage

The force or pressure from a power source that pushes charged electrons through a circuit.

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Resistance

The measure of opposition to the flow of electric current in a circuit, measured in Ohms.

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Series Circuit

A circuit where there is only one path for the electric current to follow.

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Parallel Circuit

A circuit providing more than one path for the current to split and flow.

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What is an Electric Circuit?

• An electric circuit is a closed path that allows a flow of electrons.

• This steady flow of electrons is called an electric current.

• Circuits need a voltage source, like a battery, to provide a push.

• They also need a conductor, like a wire, for the current to flow.

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Multiple Choice

What are the two minimum components required for an electric circuit to function?

• A conductor and a switch

• A voltage source and a conductor

• A battery and a light bulb

• A light bulb and a switch

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Circuit Control and Energy

Open Circuit

• An open switch creates a gap, breaking the circuit's path.

• This break stops the flow of electric current completely.

• As a result, the light bulb will not light up.

Closed Circuit

• A closed switch completes the path, creating a full loop.

• Electric current can flow from the battery to the bulb.

• The bulb transforms electrical energy into light and heat energy.

Multiple Choice

What kind of energy transformation occurs within a battery to produce electricity?

• Chemical energy to electrical energy

• Electrical energy to light energy

• Mechanical energy to chemical energy

• Thermal energy to electrical energy

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Types of Circuits: Series vs. Parallel

Series Circuit

• There is only one path for the electric current to flow through the circuit.

• If the path is broken at any point, the entire circuit stops working.

• Adding more light bulbs to the circuit makes all the bulbs dimmer.

Parallel Circuit

• There are multiple paths for the electric current to flow through the circuit.

• If one bulb goes out, the other bulbs on different paths will stay lit.

• Adding more light bulbs in parallel does not change the brightness of the bulbs.

Multiple Choice

Why do the other light bulbs in a parallel circuit stay lit if one bulb goes out?

• There are multiple pathways for the current to flow.

• The voltage from the battery increases.

• The total resistance of the circuit increases.

• The circuit converts from parallel to series.

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Ohm's Law, Resistance, and Power

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Multiple Choice

According to Ohm's Law $$V=IR$$ , what happens to the current (I) in a circuit if the resistance (R) is increased while the voltage (V) stays the same?

• The current increases.

• The current stays the same.

• The current decreases.

• The current becomes zero.

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Calculating Resistance in Circuits

Series Circuits

Parallel Circuits

Multiple Choice

If a series circuit has three resistors with values of 5 Ω, 10 Ω, and 15 Ω, what is the total resistance?

• 30 Ω

• 2.7 Ω

• 0.33 Ω

• 15 Ω

Advanced Circuit Principles

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Current Law (Junction)

• Total current entering a junction equals the total current leaving it.

• This rule applies to any point where multiple wires are connected.

• It shows that electric charge is always conserved in a circuit.

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Voltage Law (Loop)

• The total voltage supplied to a loop equals the total voltage used.

• This applies to any complete, closed path within the electrical circuit.

• This law demonstrates the conservation of energy in the electrical circuit.

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Capacitors

• Capacitors are special components that can store electrical energy for later.

• They work by holding charge in a generated electric field.

• Their storage ability is called capacitance, measured in units called Farads.

Multiple Choice

Which principle states that the total current entering a junction must equal the total current leaving it?

• Kirchhoff's Voltage Law

• The law of conservation of energy

• Kirchhoff's Current Law

• Ohm's Law

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Common Misconceptions About Electricity

Misconception	Correction
Electric current is 'used up' in a circuit.	Energy is transformed, but the electric current keeps flowing through the circuit.
Batteries create new energy.	Batteries change stored chemical energy into electrical energy.
Turning a switch 'off' closes the circuit.	Turning a switch 'off' opens the circuit, stopping the current's flow.

Multiple Choice

If you have a string of lights in a series circuit and you add more light bulbs, what will be the effect on the brightness of the bulbs and why?

• They will get dimmer because the voltage decreases.

• They will get brighter because the current increases.

• They will get dimmer because the total resistance increases.

• They will not change in brightness.

Multiple Choice

In a home circuit with a fixed voltage of 120V, what happens to the current if you connect a device with very high resistance?

• The current drawn will be very high.

• The circuit will switch from parallel to series.

• The voltage of the circuit will drop.

• The current drawn will be very low.

Multiple Choice

Analyze a parallel circuit with three light bulbs. If one bulb's filament breaks, why do the other two bulbs continue to function, and what happens to the total resistance of the circuit?

• The other bulbs go out because the circuit is now open, and the total resistance becomes infinite.

• The other bulbs stay lit because there are still complete paths for current, and the total resistance of the circuit increases.

• The other bulbs stay lit because the battery's voltage increases, and the total resistance of the circuit decreases.

• The other bulbs get brighter because the current is redirected, and the total resistance stays the same.

Multiple Choice

A device is connected to a circuit. How could you increase the power consumed by the device without changing the voltage of the power source?

• Add a switch and turn it off.

• Add a second device in series with the first.

• Increase the device's resistance to decrease the current.

• Decrease the device's resistance to increase the current.

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Summary

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

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• 4