Series and parallel circuits

There are two kinds of electrical circuit. These are called series circuits and parallel circuits.
In series circuit current has only one path to follow, i.e. there are no branches.
In a series circuit the same current passes through all parts. If one of the bulbs in the circuit below is turned off, they are all turned off.
In a parallel circuit there are several paths electricity can follow, i.e. there are branches.
In a parallel circuit it is possible to switch off some parts of the circuit and yet leave others on, as shown in figure 4.
Measuring current:
The size of a current is measured using an instrument called an ammeter. Current is measured in units called amps (A). The ammeter is placed in series with the part of the circuit being investigated.
Currents in series circuits:
• Ammeter A is measuring how much current is leaving the cell.
• Ammeter B is reading how much current is flowing into the resistor.
• Ammeter C is reading how much current is flowing into the bulb.
• Ammeter D is reading how much current is flowing back into the cell.
From these readings it is clear that:
1. The current leaving the cell is the same size as the current returning to it. Current is not used up as it flows around a circuit.
2. The size of the current is the same in all parts of a series circuit.

Current in parallel circuit:• Ammeter A is measuring how much current is leaving the cell.
• Ammeter B is reading how much current is flowing through the bulb.
• Ammeter C is reading how much current is flowing through the resistor.
• Ammeter D is reading how much current is flowing back into the cell.

From these readings it is clear that:
1. The size of the current in different parts of a parallel circuit is not the same.
2. The current leaving the cell is the same size as the current returning to it.
3. The current entering a junction is equal to 0.5 A= 0.2 A + 0.3 A.

Energy in circuits:
As current passes through a cell or a battery it receives electrical energy which it carries around the circuit. This energy ischanged into other forms as the current passes through the various components. For example when current passes through a bulb, some of the electrical energy it is carrying is changed into heat and light energy. If the current passes through a buzzer, some of the energy ischanged into sound.
We can measure how much energy is given to the electricity as it passes through the cell or battery, and how much electrical energy is transformed in the various components in a circuit using a voltmeter. The voltmeter is connected in parallel with the part of the circuit we are interested in. large voltage readings indicate large energy transfers by the components.
Note that the voltmeter reading across the cell is equal to the sum of the voltmeter readings across the bulb and the buzzer. This indicates that all electrical energy received by the current as it passes through the cell is converted to other forms of energy by the components in the circuit.