Parallel and Series Circuits

Symbols of electric circuit components

To make the drawing of an electric circuit easier, components of an electric circuit should be represented by certain symbols.

Electric circuit

  1. An electric circuit is a path that allows electric current to flow through it.
  2. The bulb will light up or the ammeter needle will deflect if an electric circuit is connected correctly.
  3. There are two types of electric circuits, i.e.:
    1. series circuit
    2. parallel circuit

Series circuit

  1. When circuit components like bulbs or resistors are connected from end to end or in a row, the circuit is called a series circuit.
  2. The electric current flows on only one path from the positive terminal to the negative terminal of an electric source.
  3. In a series circuit, if one part of the circuit is disconnected or a bulb is burnt, the circuit becomes incomplete and other bulbs will also be put out.

Parallel circuit

  1. In a parallel circuit, electric components are arranged side by side and parallel to one another.
  2. There is more than one path for the flow of electric current.
  3. In a parallel circuit, if one bulb or resistor is spoilt or removed, electric current will still flow through another path. Other bulbs are still lit.
  4. This type of circuit is used in buildings like homes and schools. Damage to one part of an electric circuit can be traced at once.

Electric Current, Voltage and Resistance in a Series Circuit

Flow of electric current in a series circuit


  1. The ammeter gives the same reading even though it is connected at different positions. This shows that the current that flows in all the positions in a series circuit is the same.
  2. If the current that flows through the ammeter X, Y dan Z are represented respectively by symbols I, /1 and 12, then the current values for I,11 and 12 are the same, i.e.:

Voltage in a series circuit

Voltage of cells in series
  1. The more cells that are connected in series, the greater the current that flows. This is because more cells supply greater voltage or electrical energy to the circuit.
  2. The total voltage is the same as the sum of the voltages of each cell.
Voltage of bulbs in series
  1. The voltage across every circuit component like the bulb (or resistor) in a series circuit is the same.
  2. If the voltage that is supplied by an electric source is represented by the symbol V and bulbs X and Y respectively use voltage value V1 and V2, then the relationship between V, V1 and V2 is

Resistance in a series circuit

  1. If more bulbs are added in series, resistance in the circuit will increase causing the current that flows through the bulbs to decrease. Therefore, the bulbs will shine dimly.
  2. If resistance of the bulbs is represented by R1 and R2, resistance (R) in a series circuit is the sum of the resistance in each bulb, i.e.:

Advantages and disadvantages of a series circuit

  1. The advantages of a series circuit are as follows:
    1. Current in all parts of the circuit is the same. This causes the bulbs to light up with the same brightness.
    2. The current in the circuit increases if more cells are connected.
    3. All circuit components are controlled by one switch.
  2. The disadvantages of a series circuit are as follows:
    1. There is only one path for the flow of electric current. If a bulb or lamp is burnt, other bulbs will not light up.
    2. Cells in series do not last long.
    3. If more bulbs are added, the resistance in the circuit increases causing the electric current that flows to decrease.

Electric Current, Voltage and Resistance in a Parallel Circuit low of electric current in a parallel circuit

  1. In a parallel circuit, the quantity of current supplied by the electric source will be channelled to the branches according to their resistance value.
  2. The quantity of current supplied by the electric source in a parallel circuit is same as the sum of the current that flows through each branch path.
  3. If the current flowing through ammeter P, Q and R is represented by symbols I, II and 12 respectively, then the ampere value relationship of I, II and 12 is as follows.

Voltage in a parallel circuit

Voltage of cells in parallel
  1. Voltage does not increase or decrease if cells of the same type are connected in parallel.
  2. Compared to cells in series, cells in parallel are more lasting. The more cells there are in a parallel arrangement, the more lasting they are as electrical energy
Voltage of bulbs in parallel
  1. The voltage across each bulb is the same as the voltage supplied by the electric source.
  2. If the voltage recorded by the voltmeter at positions P, Q and R in Figure below are represented by symbols V, V1 and V2 respectively, then the voltage value relationship of V, V1 and V2 is as follows.

Resistance in a parallel circuit

If R is the total resistance and the resistance of the resistors in Figure below is represented by R1 and R2 respectively, then the relationship between R, R1 and R2 in the parallel circuit is

Advantages and disadvantages of a parallel circuit

  1. The advantages of a parallel circuit are as follows:
    1. If one of the bulbs is burnt, the other bulb(s) continues to shine.
    2. Parallel cells last longer.
    3. Each bulb receives the same voltage that is supplied by the electric source.
  2. The disadvantages of a parallel circuit are as follows:
    1. The voltage does not increase or decrease if cells of the same type are connected in parallel.
    2. The electric current in the circuit is the same even though more cells are connected in parallel.