LESSON 03 – SERIES CIRCUITS

 

 

LESSON NOTE

SERIES CIRCUITS

 

A series circuit is simply a circuit that contains a single path.

 

PROPERTIES OF SERIES CIRCUITS

 

  • The current is constant throughout because there is only one path to follow (Kirchoff’s Current Law).
  • The voltage drop over all the loads is the same amount as the voltage of your source/battery (Kirchoff’s Voltage Law).
  • The total resistance of your circuit is equal to the sum of all resistances.


SOLVING FOR ALL UNKNOWNS

To solve for all unknowns for a circuit, we need to find the voltage drop, the current and the resistance for the entire circuit as well as at each load.  We usually organized our answers in a table.

 

The table has three columns – one for voltage drop, one for current and one for resistance.

The table has one row for the total circuit and one row for each load.

For example, let’s consider the circuit below:

 

To solve all unknowns for the above circuit, we would build the following table:

 

VT

IT

RT

V1

I1

R1

V2

I2

R2

V3

I3

R3

V4

I4

R4

 
The first row represents the voltage drop, current and resistance for the total circuit.  The next row is the voltage drop, current and resistance at the first load.  The following row is for the second load.  And so on…

 

ABOUT THE ROWS OF THE TABLE

 

For any row, if we have a single unknown, we can use Ohm’s Law to solve for that unknown.

ABOUT THE COLUMNS OF THE TABLE

We can also solve for a single unknown in columns.  However, this requires that we use the properties of series circuits.

 

So, for voltage, we know that the total voltage down (VT) is equal to V1 + V2 + V3 + …

 

For current, we know that the current is the same everywhere. So IT = I1 = I2 = I3 = …

 

For resistance, we know that RT = R1 + R2 + R3 + …