5.  TYPES OF CIRCUITS

Circuits exist in all kinds of different places. The lighting in school or home, street lights, torches and alarm systems all have circuits that are fairly simple.

Circuits are found in calculators, computers, televisions, radios, cars, medical equipment, aircraft, the Internet, factories, telephones and many more places.

We shall look at some of these connections.

5.1.  Association of batteries

Cells and batteries are useful sources of electricity. They transfer chemical energy to electrical energy.

A zinc-carbon cell (dry Leclaché cell): This is the common cell used in torches. The voltage across the cell is 1.5V. Once the chemicals are used up you throw it away.

There are also re-chargeable batteries. For example, a lead-acid battery in a car turns the starter motor and is then re-charged when the engine is running. During re-charging, energy is store in the battery.

We shall look at some ways of connecting batteries.

  • Batteries in series
When we connect in a circuit several batteries in series, the total voltage increases and the current gets larger.
In circuit C, the batteries give 3 volts. The lamp will be very bright. /
As we can see, in circuit C, the batteries give 3 volts. The lamp will be very bright.
  • Batteries in parallel
When batteries are connected in parallel their voltages don’t add up. The reason for connecting batteries in parallel is that two batteries last longer than one and can supply a higher current if needed.
As we can see, in circuit B, the batteries give 1.5 volts. The lamp will have normal brightness (as in circuit A) but the batteries will last twice as long as those in circuit A.

5.2.  Series circuit

Components that are placed one after another in the circuit are connected in series. The current that flows across each component has the same value.

The diagram on the right shows a circuit with two lamps connected in series. If one lamp breaks, the other lamp will not light. /
This circuit is another example of series circuit. Different types of components can be connected in series. /

5.3.  Parallel circuit

If we connect several electric components as shown in the figure on the right, we say that they are connected in parallel. /
The scheme on the right shows a circuit with two lamps connected in parallel. If one lamp breaks, the other lamp will still light. /
/ Series circuit / Parallel circuit /
Scheme of the circuit / / /
Resistance / The effect is to add more resistance to the circuit
/ The effect is to reduce the resistance of the circuit
/
Voltage / The voltage of the supply is shared between the components in series
/ The voltage across each component in parallel, is the same
/
Current / The current that flows across each component connected in series is the same
/ The current is shared between each component connected in parallel
/
/ Series Circuit / Parallel Circuit /
Resistance rules / Total resistance is greater than every single resistance of the circuit / Total resistance is smaller than the smallest of the resistance connected in parallel.
Current rules / Current is the same in every point of the circuit
As the number of appliances increases in the circuit, the resistance gets larger and the current gets smaller / The sum of currents approaching a junction is the same than the one leaving that junction
More current goes through the easier path (the one with less resistance)
Voltage rules / Total voltage is shared between all the appliances of the circuit.
Battery voltage is equal to the sum of voltages in every appliance of the circuit / Appliances in parallel get the same voltage
Battery voltage is equal to the voltage in every appliance of the circuit.

5.4.  Mixed circuit

If a circuit has components connected both in series and in parallel, we call it a mixed circuit.

Examples of circuits:

Series circuit

Parallel circuit

V1=V2=V3 = 12 V

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