Ohm's Law

Learning objectives

By the end of this module, the learner should be able to:

• explain the relationship between voltage, current, and resistance;
• calculate voltage, current, or resistance when two quantities are known;
• interpret a voltage-current graph for an ohmic component;
• explain why power dissipation matters in electrical design.

First-principles explanation

In a simple electrical circuit, voltage provides the electrical potential difference that drives charge through a component. Current is the rate of flow of charge. Resistance is the opposition to that flow.

For an ohmic conductor at constant temperature, current is directly proportional to voltage. This proportionality is described by Ohm's Law.

Equation and units

• V is voltage, measured in volts (V).
• I is current, measured in amperes (A).
• R is resistance, measured in ohms (Ω).

Rearranged forms:

• I = V / R
• R = V / I

Worked example

Problem: A 100 Ω resistor is connected across a 10 V supply. Find the current.

Known values:

• Voltage, V = 10 V
• Resistance, R = 100 Ω

Calculation:

I = V / R = 10 / 100 = 0.10 A

Answer: The current is 0.10 A, or 100 mA.

Interactive simulator

The Ohm's Law simulator lets the learner adjust voltage and resistance, then observe the effect on current and power dissipation.

Local launch command:

python -m streamlit run simulations/ohms_law/streamlit_web_app.py --server.port 8501

Engineering meaning

Ohm's Law is one of the first tools used in circuit design. It helps engineers choose resistors, estimate current draw, protect components, and understand why electrical systems heat up under load.

Power is especially important. Since P = V² / R, doubling the voltage can quadruple the power dissipated in a resistor.

Assumptions and limits

• The component is ohmic.
• Temperature is treated as constant.
• Resistance does not change with current or voltage.
• Capacitance, inductance, and transient effects are ignored.

Challenge questions

1. If a 220 Ω resistor is connected to 5 V, what current flows?
2. If current doubles while resistance is constant, what happens to voltage?
3. Why can excessive current damage a component?
4. What assumption breaks down if a resistor becomes very hot?