Notes on Total Energy Transfer in Circuits

Understanding Total Energy Transferred in Electrical Circuits

  • Basic Concepts

    • In electrical circuits, when charge flows, work is done, and energy is transferred.

  • Equations to Remember

    • Total Charge Flow:
    • To calculate the total charge ($Q$) in coulombs: Q=IimestQ = I imes t
      • Where:
      • $Q$ = total charge in coulombs
      • $I$ = current in amps
      • $t$ = time in seconds
      • Example Calculation:
      • Current = 0.3 A, Time = 10 s
      • Q=0.3imes10=3extcoulombsQ = 0.3 imes 10 = 3 ext{ coulombs}

  • Energy Transferred

    • Equation for energy transferred ($E$) in joules:
    • E=QimesVE = Q imes V
      • Where:
      • $E$ = energy transferred in joules
      • $Q$ = charge flow in coulombs
      • $V$ = potential difference in volts
      • Important: This equation is not provided in exams; it must be memorized.

  • Example Problem 1

    • Given:
    • Charge flow = 4 coulombs
    • Potential difference = 15 volts
    • Calculation:
    • E=4imes15=60extjoulesE = 4 imes 15 = 60 ext{ joules}
    • Thus, the total energy transferred = 60 joules.

  • Example Problem 2

    • Scenario with series resistors:
    • Given:
      • Charge flow = 3 coulombs
      • Total potential difference of the cell = 30 volts
      • Resistor B potential difference = 25 volts
    • Find potential difference across Resistor A:
      • Potential difference across Resistor A = Total potential - Resistor B potential
      • VA=30−25=5extvoltsV_A = 30 - 25 = 5 ext{ volts}
    • Calculation for energy transferred in Resistor A:
    • E=3imes5=15extjoulesE = 3 imes 5 = 15 ext{ joules}
    • Energy transferred by resistor A = 15 joules.