# 3.3 Series and parallel circuits serve different purposes in households

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## 3. Series and parallel circuits serve different purposes in households

### 1. identify the difference between series and parallel circuits

Series is when the components line up after one another, thus there is only 1 path. In parallel there are multiple paths.

Advantages of using parallel circuitry over series circuitry in household wiring include:

• You can have some devices on and others off at the same time.
• If one device fails the others still work.
• All devices receive the highest possible voltage.

### 2. compare parallel and series circuits in terms of voltage across components and current through them

In a series circuit voltage is divided evenly throughout the components, with current being the same max current throughout all the components. In a parallel circuit it is opposite, voltage is the same max voltage throughout the components, with current being divided evenly throughout the components.

In the series circuit each light will be half the brightness than if there was only one. However in the parallel circuit the lights have the same brightness no matter how many are added.

### 3. identify uses of ammeters and voltmeters

Ammeters are used to measure current. Voltmeters are used to measure voltage. To measure the voltage of a component the voltmeter is placed in parallel with the component. To measure the current passing through a component, the ammeter is placed in series with the component. When an ammeters work best if they have a low resistance. And voltmeters work best if they have a high resistance.

### 4. explain why ammeters and voltmeters are connected differently in a circuit

Voltage is sometimes called potential difference. So it is measuring the difference between two points, so is must be placed in parallel so that it can measure the difference between before and after that component.

Current is a measure of the rate at which charge flows, and therefore must be connected in series. Ammeters have a low resistance.

In parallel:

VTOTAL = V1 = V2 = V3

ITOTAL = I1 + I2 + I3

$\frac {1}{R_{TOTAL}} = \frac {1}{R_1} + \frac {1}{R_2} + \frac {1}{R_3}$

In Series:

ITOTAL = I1 = I2 = I3

VTOTAL = V1 + V2 + V3

RTOTAL = R1 + R2 + R3




Example: (Finding Current, Resistance and Voltage around a circuit)

Total: Total Resistance = $\frac {1}{\frac {1}{6} + \frac {1}{3}}$ = 2 Ω V = IR 12 = $I_{TOTAL} \times 2$ ITOTAL = 6 Amps

Resistor 1: $12 = I \times 6$ I1 = 2

Resistor 2: $12 = I \times 3$ I2 = 4

I1 + I2 = ITOTAL 2 + 4 = 6

Total: Total Resistance = 1 + 2 = 3Ω $12 = I \times 3$ I = 4 Amps

As ITOTAL = I1 = I2 = I3 I1 = 4 I2 = 4

Resistor 1: $V = 4 \times 1$ V = 4

Resistor 2: $V = 4 \times 2$ V = 8

VTOTAL = V1 + V2 + V3

And this works 12 = 8 + 4

### 5. explain why there are different circuits for lighting, heating and other appliances in a house

Electricity delivered to household appliances is AC 240V, 10A. Power = 2400W. Heaters use roughly 1000W, so if all the appliances were on the same circuit there would simply be not enough power to serve all the appliances.

### 7. plan, choose equipment or resources and perform a first-hand investigation to construct simple model household circuits using electrical components

To calculate the total resistance in a series circuit you add all the resistances together. RT = R1 + R2 + R3 + ...

To calculate the total resistance in a parallel circuit you add the inverse of the resistances together, this will give you the inverse of the total resistance.

$\frac {1}{R_T} = \frac {1}{R_1} + \frac {1}{R_2} + \frac {1}{R_3} + ...$