P13.2 – Series and Parallel Circuits

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Components connected in series are connected along a single path, while those connected in parallel are connected along different paths.

1. Demonstrate understanding that the current at every point in a series circuit is the same.

Simple. Current in a circuit is same anywhere in a series circuit. Which is why you can connect an ammeter anywhere in the circuit and you’ll get the same value in amperes.

2. Recall and use the fact that the sum of the p.d.s across the components in a series circuit is equal to the total p.d. across the supply.

The total p.d. of in a series circuit will be the sum of the p.d. across each component in the circuit. Example:

3. Calculate the combined resistance of two or more resistors in series.

The total resistance in a series circuit is the sum of the resistance of all the resistors in the circuit.

 

4. State that, for a parallel circuit, the current from the source is larger than the current in each branch.

In a parallel circuit, since the current flowing from the source/battery is larger than the current in each branch (i.e. each straight wire). We’ll take a look at this next.

5. Recall and use the fact that the current from the source is the sum of the currents in the separate branches of a parallel circuit.

The current from the source, of a parallel circuit, is the sum of the separate branches in the circuit. The current breaks up and take the easiest path first, with some flowing along each parallel branch and re-combining when the branches meet again. Confused? Let’s take a look at this example from the BBC website:
Conventional current flows from the positive end (long line) to the negative end (short line). The current at point 1 will be 0.2 A. It then splits into two branches, and so at points 2 and 4, the current will halve, i.e, 0.1 A each. And finally at point 3, the current will join back at 0.2 A.

6. State that the combined resistance of two resistors in parallel is less than that of either resistor by itself.

The combined resistance of the resistors in a parallel circuit is less than that of the individual resistors.

7. Calculate the effective resistance of two resistors in parallel.

The total resistance of the resistors in a parallel circuit can be calculated by using any of these equation (R₁ is resistor 1, R₂ is resistor 2 and so on):

8. State the advantages of connecting lamps in parallel in a lighting circuit.

Why are some circuits connected in parallel, when a series circuit is much more easier and requires lesser amount of wire? Let’s look at the advantages of a parallel circuit, in the instance of lighting bulbs:

• • the voltage across each bulb will be the same, so every bulb will be equally bright
  • each component is independent of other. In a series circuit, if one component breaks down, the entire circuit will be affected. But in a parallel circuit, there are multiple paths for the current to flow.
  • Each component can be independently controlled by a switch. In a series circuit, one switch controls every component. In a parallel circuit, you can connect switches parallel for component in different branches, to turn them off or on.

 

 

Notes submitted by Lintha

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