Ohm's Law

Ohm's Law

High School

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Learning Objectives

• Define Ohm's Law and its key components: voltage, current, and resistance.

• Analyze the differences between series and parallel circuits.

• Apply Ohm's Law formulas to calculate unknown values in a circuit.

• Understand the relationship between power, voltage, current, and resistance.

• Identify the correct formula to use for a given electrical problem.

Key Vocabulary

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Voltage (V)

The potential difference or electrical 'pressure' that pushes electric charges to move through a circuit.

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Current (I)

The rate at which electric charge flows past a point in a complete electrical circuit.

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Resistance (R)

A measure of the opposition to current flow in an electrical circuit, slowing down electrons.

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Series Circuit

A circuit where all elements are connected in a single loop, providing one path for current.

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Parallel Circuit

A circuit with several pathways, allowing electrons to flow through more than one path.

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What is Ohm's Law?

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Solved Example 1
What is the voltage across a 3 Ω resistor if a current of 4 A flows through it?

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Step 1: Analyze and Sketch the Problem

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Solved Example 1
What is the voltage across a 3 Ω resistor if a current of 4 A flows through it?

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Step 2: Solve for the Unknown

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Solved Example 1
What is the voltage across a 3 Ω resistor if a current of 4 A flows through it?

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Step 3: Evaluate the Answer

Multiple Choice

According to Ohm's Law, if the voltage in a circuit is doubled while the resistance remains constant, what happens to the current?

• It becomes zero.

• It remains the same.

• It is halved.

• It is doubled.

Key Components: Voltage, Current, & Resistance

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Voltage (V)

• ​It is the "push" or pressure that moves electric charges.

• ​​The potential difference that makes the electric charges flow.

• ​Measured in Volts (V) and provided by a power source.

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Current (I)

• ​The rate at which an electric charge flows past a point.

• ​​When electrons move faster, the electric current is greater.

• ​It is measured in Amperes, also known as Amps (A).

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Resistance (R)

• ​The measure of opposition to the flow of an electric current.

• ​​It makes it harder for the electrons to be able to move.

• ​This is measured in a unit known as Ohms (Ω).

Multiple Choice

In the water pipe analogy for circuits, what does the friction or sand that slows the water represent?

• Power (P)

• Current (I)

• Voltage (V)

• Resistance (R)

Series vs. Parallel Circuits

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Series Circuits

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Parallel Circuits

• Components are on separate branches, providing multiple pathways for the current.

• If one bulb burns out, the other bulbs will stay lit.

• The voltage across each branch of the circuit remains the same.

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Combined Circuits

• Some circuits have a combination of series and parallel sections.

• You must apply rules for each circuit type to analyze them.

• The rules are applied to the corresponding circuit sections.

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Solved Example 3
A series circuit contains a 12V battery and three resistors with values of 2Ω, 4Ω, and 6Ω. What is the total resistance of the circuit and the total current flowing through it?

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Step 1: Analyze and Sketch the Problem

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Solved Example 3
A series circuit contains a 12V battery and three resistors with values of 2Ω, 4Ω, and 6Ω. What is the total resistance of the circuit and the total current flowing through it?

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Step 2: Solve for the Unknown

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Solved Example 3
A series circuit contains a 12V battery and three resistors with values of 2Ω, 4Ω, and 6Ω. What is the total resistance of the circuit and the total current flowing through it?

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Step 3: Evaluate the Answer

Multiple Choice

A string of holiday lights has three bulbs. When one bulb is removed, the other two go out. What kind of circuit is this?

• A series circuit

• A parallel circuit

• A short circuit

• A combined circuit

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What Is Electrical Power?

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Solved Example 4
A circuit contains a resistor with a resistance of 3 Ω and is connected to a 12 V battery. What is the power dissipated by the resistor?

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Step 1: Analyze and Sketch the Problem

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Solved Example 4
A circuit contains a resistor with a resistance of 3 Ω and is connected to a 12 V battery. What is the power dissipated by the resistor?

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Step 2: Solve for the Unknown

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Solved Example 4
A circuit contains a resistor with a resistance of 3 Ω and is connected to a 12 V battery. What is the power dissipated by the resistor?

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Step 3: Evaluate the Answer

Multiple Choice

Which of the following formulas correctly calculates the electrical power (P) in a circuit?

• $$P = I^2 \times R$$

• $$P = I / V$$

• $$P = V / R$$

• $$P = V \times R$$

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Common Misconceptions about Circuits

Multiple Choice

A circuit has a 24V battery and a single 6-ohm resistor. If a second 6-ohm resistor is added in series, what is the effect on the total current flowing from the battery?

• The current doubles.

• The current becomes zero.

• The current stays the same.

• The current is halved.

Multiple Choice

A heating element is rated at 576 Watts and is used in a standard 120V household circuit. Based on the power formulas, what is the resistance of the heating element?

• 4.8 Ohms

• 25 Ohms

• 0.2 Ohms

• 576 Ohms

Multiple Choice

You have a 5-ohm resistor and a 10-ohm resistor. To achieve the highest possible current from a 15V battery, how should you connect them and what will the current be?

• In series; the current will be 1.0 A.

• In series; the current will be 1.5 A.

• In parallel; the current will be 3.0 A.

• In parallel; the current will be 4.5 A.

Multiple Choice

A circuit with a 40V source has a current of 10A with resistor R₁. When R₁ is replaced by R₂, the current is 5A. Predict the total current if R₁ and R₂ are then connected in parallel to the same 40V source.

• 15 A

• 10 A

• 2.5 A

• 5 A

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Summary

Poll

On a scale of 1-4, how confident are you about using Ohm's Law to solve circuit problems?

• 1

• 2

• 3

• 4