KinexiaLEARN PHYSICS

Electric Potential — Defibrillator Charge (Worked Example)

Medium
Problem

A defibrillator delivers 200 J of energy at 1500 V across the chest. How much charge flows during the shock?

Given

  • W = 200 J

  • V = 1500 V

Find

The charge q.

Principle

Rearranging V = W/q gives q = W/V — energy divided by voltage is charge.

Formula

Solution

  1. Rearrange: q=W/Vq = W/V

  2. Substitute: q=200/1500q = 200/1500

  3. Divide: q=0.133 Cq = 0.133\ \mathrm{C}

0.133 C

Unit check

J ÷ V = J ÷ (J/C) = C — correct.

What this means physically

0.133 C — a large charge delivered in milliseconds, which is why the current (charge ÷ time) is huge and can reset the heart's rhythm.

Common mistake

Multiplying W × V. Check units: J × V is not coulombs — only W/V gives charge.