How It Works: Why AC Peaks at 325 V But We Say 230 V
Part of Mains Electricity & Safety — GCSE Physics
This how it works covers How It Works: Why AC Peaks at 325 V But We Say 230 V within Mains Electricity & Safety for GCSE Physics. Revise Mains Electricity & Safety in Electricity for GCSE Physics with 13 exam-style questions and 30 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 8 of 17 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 8 of 17
Practice
13 questions
Recall
30 flashcards
⚙️ How It Works: Why AC Peaks at 325 V But We Say 230 V
AC mains voltage constantly alternates between positive and negative values. In the UK, it peaks at approximately +325 V and -325 V. So why do we say the mains is 230 V?
230 V is the RMS (root mean square) voltage — a mathematical average that takes into account the constantly changing direction and magnitude of AC. RMS voltage is the equivalent DC voltage that would deliver the same power to a resistive load.
The formula relating peak to RMS is: Vrms = Vpeak / √2. Since √2 ≈ 1.41: Vrms = 325 / 1.41 ≈ 230 V.
This is important for safety: the live wire is always at a potentially lethal voltage, even when an appliance is switched off, because it's still connected to the supply at the socket.
Quick Check: What colour is the live wire in a UK plug, and what is its function?
The live wire is brown. It carries current to the appliance at alternating voltages between +325 V and -325 V (230 V RMS). It is always dangerous, even when the appliance is switched off but still plugged in.