Symbol Name Unit Unit Symbol Rtotal Total Resistance ohms Ω R1 Resistance 1 ohms Ω R2 Resistance 2 ohms Ω R3etc Other resistors ohms Ω In this equation we put … at the end as there can be any number of resistances. Worked examples Calculate the resistance of the circuit shown below Rtotal = ? 1/Rtotal = 1/R1 + 1/R2 + 1/R3 R1 = 100 Ω 1/Rtotal = 1/100 + 1/200 + 1/400 R2 = 200 Ω 1/Rtotal = 4/400 + 2/400 + 1/400 R3 = 400 Ω 1/Rtotal = 7/400 7 × = 1×400 The total resistance of Rtotal = 400/7 this circuit is 100Ω. Rtotal = 57 Ω Calculate the value of Rtotal Resistor 1 Rtotal = 100 1/Rtotal = 1/R1 + 1/R2 Ω 1/100 = 1/R1 + 1/200 R1 = ? 1/R1 = 1/100 - 1/200 R2 = 200 1/R1 = 2/200 - 1/200 Ω 1/R1 = 1/200 R1 = 200 Ω Measuring Current, Voltage and Resistance Like all components, meters (which are used to measure values) have component symbols. Component Name Circuit Symbol Function Measures potential difference. Must be placed in parallel to measure the Voltmeter difference in electrical potential between two points. Measures current. Must be placed in series Ammeter to measure the current flowing in a circuit.
Symbol Name Unit Unit Symbol Rtotal Total Resistance ohms Ω R1 Resistance 1 ohms Ω R2 Resistance 2 ohms Ω R3etc Other resistors ohms Ω In this equation we put … at the end as there can be any number of resistances. Worked examples Calculate the resistance of the circuit shown below Rtotal = ? R1 = 100 Ω R2 = 200 Ω R3 = 400 Ω 1/Rtotal 1/Rtotal 1/Rtotal 1/Rtotal 7 × Rtotal Rtotal Rtotal = 1/R1 + 1/R2 + 1/R3 = 1/100 + 1/200 + 1/400 = 4/400 + 2/400 + 1/400 = 7/400 = 1×400 = 400/7 = 57 Ω The total resistance of this circuit is 100Ω. Calculate the value of Resistor 1 Rtotal = 100 Ω R1 = ? R2 = 200 Ω 1/Rtotal 1/100 1/R1 1/R1 1/R1 R1 = 1/R1 + 1/R2 = 1/R1 + 1/200 = 1/100 - 1/200 = 2/200 - 1/200 = 1/200 = 200 Ω Measuring Current, Voltage and Resistance Like all components, meters (which are used to measure values) have component symbols. Component Name Circuit Symbol Function Voltmeter Measures potential difference. Must be placed in parallel to measure the difference in electrical potential between two points. Ammeter Measures current. Must be placed in series to measure the current flowing in a circuit.