Equivalent Resistance Objectives: 3.7 Distinguish the equivalent resistance of series and parallel circuits kept at constant temperatures. 3.8 Determine the equivalent resistance of a series- parallel circuit kept at constant temperature. 3.9 Evaluate the significance of the error in the measurement of electrical resistance.

Equivalent or Total Resistance - Req Equivalent Resistance is the TOTAL resistance of a circuit Symbol: Req or Rt Units: Ω Ohms Formula: Series: Req = R1 + R2 + R3 + … Parallel:

What is the equivalent resistance (Req) of the circuit below? Example #1: What is the equivalent resistance (Req) of the circuit below? 5 W 3 W 10 W Type of circuit: Series Formula: Req = R1 + R2 + R3 Req = 10 + 5 + 3 Req = 18 W

What is the equivalent resistance (Req) of the circuit below? Example #2: What is the equivalent resistance (Req) of the circuit below? 30 W 75 W Type of circuit: Series Formula: Req = R1 + R2 Req = 75 +30 Req = 105 W

What is the equivalent resistance (Req) of the circuit below? Example #3: What is the equivalent resistance (Req) of the circuit below? 10 Ω 15 Ω Type of circuit: Parallel Formula: 1 ÷ 0.1666 = 6Ω

What is the equivalent resistance (Req) of the circuit below? Example #4: 15 W 5 W Type of circuit: Parallel Formula: 1 ÷ 0.3333 = 3Ω

KEY POINTS Symbols of circuit parts: Voltmeter, Ammeter, Power Supply, Resistor Two types of circuits (series and parallel) Formula for Req (equivalent resistance) Series – Req = R1 + R2 + R3 Parallel -