Potential difference is the energy transferred per unit charge between two points. Use V = E/Q: one volt is one joule per coulomb. A voltmeter connects in parallel; a larger potential difference transfers more energy for each coulomb. Example: A component transfers 120 J when 10 C passes. Calculate its potential difference. V = E/Q = 120/10 = 12 V, or 12 J per coulomb. Rearrange the relationship before substituting if a different quantity is required. Use clear labels. Identify cause and effect.