Electrical Energy Calculations

Aug 24, 2025

Overview

This lecture covers how to calculate the total energy transferred by components in an electrical circuit using charge, current, time, and potential difference.

Calculating Charge in a Circuit

  • The total charge (Q) is found by multiplying current (I, in amperes) by time (t, in seconds): Q = I × t.
  • Example: For a current of 0.3 A over 10 seconds, Q = 0.3 × 10 = 3 coulombs (C).

Calculating Energy Transferred

  • Energy transferred (E, in joules) is calculated as charge (Q) multiplied by potential difference (V, in volts): E = Q × V.
  • This equation is not given in exams and must be memorized.
  • Example: If 4 C of charge flows through a circuit with 15 V, energy transferred is 4 × 15 = 60 J.

Series Circuits and Potential Difference

  • In series circuits, the total potential difference is shared among components.
  • To find the potential difference across one resistor, subtract the potential difference across the other from the total.
  • Example: If total V is 30 V, resistor B has 25 V, then resistor A has 5 V.

Example Problem: Energy Transferred in a Resistor

  • Use E = Q × V for specific components.
  • Example: 3 C of charge flows through resistor A with 5 V across it, so energy transferred is 3 × 5 = 15 J.

Key Terms & Definitions

  • Charge (Q) — The quantity of electricity, measured in coulombs (C).
  • Current (I) — The flow of electric charge, measured in amperes (A).
  • Time (t) — Duration, measured in seconds (s).
  • Potential Difference (V) — The energy per charge between two points, measured in volts (V).
  • Energy Transferred (E) — The work done or energy moved, measured in joules (J).
  • Series Circuit — A circuit with components arranged in a single loop, sharing total voltage.

Action Items / Next Steps

  • Memorize the equation E = Q × V.
  • Practice more calculations from the provided revision workbook or similar resources.
  • Review concepts of current, charge, potential difference, and energy calculations for circuit components.