Circuit Builder

Circuit Builder ⚡

Electricity comes down to three linked quantities: **current** (how much charge flows), **potential difference** (the push driving it) and **resistance** (what slows it down). One equation — **Ohm's law** — ties them together. Build up from the basics and every circuit question becomes readable.

Current 🌊

**Current** is the **rate of flow of charge** around a circuit, measured in **amperes (A)** with an **ammeter**. The charge that flows is **Q = I t** (charge in coulombs = current × time). A bigger current moves more charge every second.

Charge flowed

An interactive activity.

Potential difference 🔋

**Potential difference** (p.d., or voltage) is the energy given to each unit of charge — the **push** that drives the current. It is measured in **volts (V)** with a **voltmeter**. A cell with a bigger p.d. pushes harder, driving a bigger current through the same resistance.

Resistance 🧱

**Resistance** is how much a component **opposes** the current, measured in **ohms (Ω)**. A high resistance means a small current for a given p.d. Wires have very little resistance; a resistor or lamp has a lot more.

Match each quantity to its unit

Ohm's law 🟰

The three quantities are linked by **Ohm's law**: **V = I R** (potential difference = current × resistance). Rearrange it as needed: I = V ÷ R to find current, or R = V ÷ I to find resistance. One equation, three questions.

Find the potential difference

An interactive activity.

Order the method

An interactive activity.

Find the resistance

An interactive activity.

Reading a circuit 🔌

Circuits are drawn with standard **symbols**: a **cell** (long thin line + short thick line), a **resistor** (rectangle), a **lamp** (circle with a cross), and a **switch**. Meters go in different places: an **ammeter** in **series** (in the main loop), a **voltmeter** in **parallel** (across the component).

Find the resistor

An interactive activity.

Series circuits ➿

In a **series** circuit, all the components are in a single loop: • The **current** is the **same** everywhere. • The **potential difference** is **shared** between the components. • The **resistances add up** (total R = R₁ + R₂ + ...).\n\nIn **parallel**, each branch gets the full p.d., and the current **splits** between the branches.

Current in series

In a series circuit, how does the current compare at different points around the loop?

• It is the same everywhere in the circuit
• It splits between the components
• It is largest right next to the cell
• It gets used up as it goes round

The I–V characteristic 📈

Plotting **current (I)** against **potential difference (V)** reveals how a component behaves. For an **ohmic conductor** (a fixed resistor at constant temperature) the graph is a **straight line through the origin** — current is proportional to p.d. A filament lamp instead curves, because it heats up and its resistance rises.

Plot the I–V point

An interactive activity.

The circuit rules

Ohm's law states that potential difference = current × _____. Current is measured with an ammeter connected in _____ with the component. In a series circuit the current is the _____ everywhere.