Teaching guide for the module

Ohm's Law: Teacher's Guide

Teaching guide for the Ohm's Law simulator: explain in class the relationship between voltage, current and resistance, dissipated power, series and parallel configurations, and overload protection. Designed for secondary technical school teachers, electrical and electronics specialisations.

Module: Ohm's Law & Power Management · Three modes: Single · Series · Parallel

Physical phenomenon

Ohm's Law describes the linear relationship between voltage ( $V$ , in volts), current ( $I$ , in amperes) and resistance ( $R$ , in ohms) in an ohmic conductor:

$V = R \cdot I$

In an ohmic material, the current flowing through a component is directly proportional to the voltage applied across it, at constant temperature. The proportionality constant is the resistance, which depends on the material, the geometry of the conductor and temperature.

The module extends the concept to the two fundamental connection types:

Series: the same current flows through all resistors; voltages add up. Equivalent resistance is $R_{e q} = R_{1} + R_{2} + \dots$
Parallel: the same voltage is applied across all resistors; currents add up. Equivalent resistance is $\frac{1}{R _{e q}} = \frac{1}{R _{1}} + \frac{1}{R _{2}} + \dots$

Key concepts

Voltage ( $V$ ): potential difference, the "push" that sets charges in motion.
Current ( $I$ ): orderly flow of electric charges per unit time.
Resistance ( $R$ ): opposition to current flow.
Direct proportionality V↔I at fixed R, inverse I↔R at fixed V.
Voltage divider (series), voltage distributes across resistors in proportion to their values.
Current divider (parallel), current distributes inversely proportional to each branch's resistance.
Dissipated power: $P = V \cdot I = R \cdot I^{2} = V^{2} / R$ .

How to use it in the classroom

Opening: Single mode. Set R and vary V with the slider: students observe that I grows linearly. Then fix V and vary R: I decreases as R increases. Have them verbalise the relationship before writing the formula on the board.

Development: Series mode. Show two series resistors with different values (e.g. 100 Ω and 300 Ω). Guiding question: "Across which resistor is the larger voltage drop? Why?" Have students compute the expected voltage on each branch mentally before reading it from the simulator. Introduce the voltage divider concept.

Deeper exploration: Parallel mode. Same teaching pattern, with parallel resistors. Guiding question: "In which branch does more current flow?" Show that the equivalent R is smaller than the smallest of the two, the counter-intuitive point worth pinning down.

Final exercise. Assign numerical values and ask students to predict V, I and P before verifying them in the simulator. The prediction error is the most pedagogically rich moment.

Real-world examples

Current-limiting resistors for LEDs. Computing the series resistor for an LED powered by a battery, direct application of Ohm's Law.
Domestic wiring. Sockets in a room are wired in parallel to mains voltage (230 V): every appliance gets the same voltage and draws the current it needs.
Fuses and cable ratings. A cable's cross-section determines its resistance and therefore the maximum current it can carry without overheating ( $P = R I^{2}$ ).
Voltage dividers in sensors. Thermistors, photoresistors and potentiometers are placed in series with a fixed resistor to derive a voltage proportional to the measured quantity.
Photovoltaic strings. Panels are connected in series to raise voltage, in parallel to raise current.

Classroom discussion questions

If I double the voltage while keeping R constant, what happens to the current? And to the dissipated power?
In a series circuit with two resistors, can the voltage across one resistor exceed the source voltage? Why?
In a parallel circuit, why is the equivalent resistance always smaller than the smallest individual resistance?
Two equal resistors in parallel: what is the equivalent R? And in series?
A cable is heating up: what does this tell me about its resistance and the current flowing through it?

Related modules

Capacitor Charge & Discharge: the capacitor introduces the time dimension absent from the pure ohmic circuit, with an exponential transient governed by $τ = R C$ .
AC Behaviour (R, L, C): Ohm's Law extended to sinusoidal regime, where resistance becomes impedance and the phase shift between voltage and current appears.