Electricity (Years 6–11) — Science

Flick a switch and a bulb glows instantly. What actually happens is a current — a flow of tiny charged particles (electrons) — racing around a complete loop called a circuit, pushed along by the voltage of a battery.

Why this matters: current, voltage and resistance are the three quantities behind every electrical device you own. Understand how they link together and you can predict and design real circuits — and pass every electricity question in the exam.

A cell drives a current around the circuit

The water-pipe analogy

The pump (voltage) drives flow (current); a narrow pipe (resistance) slows it.

Electricity is invisible, so picture a circuit as a loop of water pipe with a pump:

Current is like the rate of water flowing past a point. It measures how much charge flows, in amps (A), read on an ammeter.
Voltage (potential difference) is like the push of the pump. It measures the driving force, in volts (V), read on a voltmeter.
Resistance is like a narrow, kinked section of pipe that slows the flow. It measures how strongly a component opposes the current, in ohms (Ω).

How to connect the meters

The two meters go in completely different ways, and mixing them up is the classic error.

Meter	Measures	Unit	Connected
Ammeter	Current	Amps (A)	In series (in the loop)
Voltmeter	Voltage	Volts (V)	In parallel (across a part)

An ammeter goes in series, right in the flow, because the current must pass through it to be counted. A voltmeter goes in parallel, bridged across a component, because it compares the push on either side.

Ammeter (A) sits in the loop; voltmeter (V) bridges across the bulb.

The key equation

Cover a letter to read its formula: V = I×R, I = V÷R, R = V÷I.

The three quantities are tied together by one relationship: V = I × R (voltage = current × resistance). Rearrange it whenever you need a different quantity: R = V ÷ I and I = V ÷ R.

Worked reasoning. A 12 V supply drives a current of 3 A through a resistor — find its resistance. Which quantity is missing? Resistance, so use R = V ÷ I. Substitute: R = 12 ÷ 3 = 4 Ω. Always check the unit at the end: dividing volts by amps gives ohms, so the answer is sensible.

Common mix-up: connecting an ammeter across a bulb (in parallel) or a voltmeter in the main loop (in series). Remember the flow: current goes through, so the ammeter joins the line; voltage is measured across, so the voltmeter bridges over the top.

Memory hook: hide the letter you want in the triangle V over I R. Cover V and you see I × R; cover R and you see V ÷ I; cover I and you see V ÷ R.