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Sometimes we need to know the exact amount of resistance provided by a group of resistors in a circuit. We may also need a circuit to have an exact amount of resistance when we need to limit the current flow for example.Depending on how the resistors in a circuit are set up (series or parallel) we can use the formulae shown in Fig 1 and Fig 2 (Rt = Total Resistance)
To calculate resistors in series (Fig 1). it is as simple as adding the resistor values together, this will give you the total resistance provided by the resistors.
In a parallel circuit (Fig 2.), the electrical flow is different going through each resistor so the calculation becomes a little more complex.
In a parallel circuit (Fig 2.), the electrical flow is different going through each resistor so the calculation becomes a little more complex.
See if you can work out the following:
Of course in real life the circuits may not always be laid out as simply as this and you may have some resistors in series and others in parallel. You would therefore need to use both formulae to work out the total resistance.
- In a series circuit R1 = 100Ω, R2 = 330Ω and R3 = 470 Ω What is the total resistance?
- In a parallel circuit, R1 = 10 Ω, R2 = 15 Ω and R3 = 20 Ω What is the total resistance?
Of course in real life the circuits may not always be laid out as simply as this and you may have some resistors in series and others in parallel. You would therefore need to use both formulae to work out the total resistance.
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