Rtotal = 25 kΩ Rtotal = R1 + R2 + R3 R1 = 12 kΩ 25000 = 12000 + R2 + 500 R2 = ? R2 = 12500 – R3 = 500 R2 = 12500 Ω R2 = 12.5 kΩ Resistors in parallel The resistors here are shown in parallel. Again, if you imagine that each resistor is a tunnel and lots of people want to get from the left to the right, this time the tunnels allow different paths for people to get through. In other words, the individual resistors will delay people, but the overall resistance is reduced compared to only having one tunnel. The total resistance of resistors in parallel will be smaller than any individual resistor. In equation form, this is Symbol Name Unit Unit Symbol Rtotal Total Resistance ohms Ω R1 Resistance 1 ohms Ω R2 Resistance 2 ohms Ω 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 1/Rtotal = 1/100 + 1/200 + 1/400 Ω R2 = 200 1/Rtotal = 4/400 + 2/400 + 1/400 Ω R3 = 400 1/Rtotal = 7/400 Ω 7 × = 1×400 The total resistance Rtotal = 400/7 of this circuit is Rtotal = 57 Ω 100Ω. Calculate the Rtotal value of Resistor 1
Rtotal R1 R2 R3 = 25 kΩ = 12 kΩ = ? = 500 Ω Rtotal 25000 R2 R2 R2 = R1 + R2 + R3 = 12000 + R2 + 500 = – 12500 = 12500 = 12.5 kΩ Resistors in parallel The resistors here are shown in parallel. Again, if you imagine that each resistor is a tunnel and lots of people want to get from the left to the right, this time the tunnels allow different paths for people to get through. In other words, the individual resistors will delay people, but the overall resistance is reduced compared to only having one tunnel. The total resistance of resistors in parallel will be smaller than any individual resistor. In equation form, this is Symbol Name Unit Unit Symbol Rtotal Total Resistance ohms Ω R1 Resistance 1 ohms Ω R2 Resistance 2 ohms Ω 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