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The figure below shows three resistors R1, R2, and R3 connected end to end i.e. in series with a battery source of V volts.
Since the circuit is closed, a current I flow and the voltage across each resistor may be determined from the voltmeter readings V1, V2, and V3.
In a series circuit:
Thus, for a series circuit, the total resistance is obtained by adding together the values of the separate resistances.
Consider the circuit below:
The voltage distribution in the above circuit is given by:
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The circuit below is normally referred to as a potential divider circuit.
This kind of circuit shown above can consist of a number of similar elements in series connected across a voltage source, voltages being taken from connections between elements. In most cases the divider consists of two resistors as shown in the circuit above; where:
A potential divider is the simplest way of producing a source of lower e.m.f. from a source of higher e.m.f. and this is the basic operating mechanism of the potentiometer, a measuring device for accurately measuring potential differences.
You can also read: Basic electric circuits
Let’s consider the circuit below:
The resistors R1, R2, and R3 in the above circuit are connected across each other i.e. in parallel, across a battery source of V volts.
In a parallel circuit:
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I = I1 + I2 + I3
Let’s consider the circuit below:
From the circuit above, the total circuit resistance RT is given by:
In an electrical circuit, the voltage at any point can be quoted as being ‘’with reference to” (w.r.t.) any other point in the circuit.
Considering the circuit below:
If a voltage at a point A is quoted with reference to point B, then the voltage is written as VAB. This is known as a relative voltage. In the circuit above, the voltage at A w.r.t. B is 2 x 40 = 80 V and written as VAB = 80 V.
We must also indicate whether the voltage at A w.r.t. B is closer to positive terminal or the negative terminal of the supply source. Point A is nearer to the positive terminal than B so is written as VAB = 80 V or VAB = +80 V or VAB = 80 V +ve.
If the voltage at B w.r.t. A is required, then VBA is negative and is written as VBA = -80 V or VBA = 80 V –ve.
If the reference point is changed to the earth point, then any voltage taken w.r.t. the earth is known as an absolute potential. If the absolute voltage of A is required, then this will be the sum of the voltages across the 40 ꭥ and 5 ꭥ resistors i.e. (40×2) + (5×2) = 90 V and is written as VA = 90 V or VA = 90 V +ve, positive since moving from earth point to point A is moving towards positive terminal of the source. If the voltage is negative w.r.t. earth then this must be indicated e.g. VC = 20 V negative w.r.t. earth and is written as VC = -20 V or VC = 20 V –ve.
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