A resistor is an electronic component used to provide

a specific amount of resistance. Generally, it can be

considered as a LOAD because loads provide
resistance to current flow.

The components of a circuit may be connected in

series or in parallel.
SERIES CIRCUIT
In a series circuit, all components are connected using
a single pathway. The current is the same for all the
components along this circuit. The total voltage is the
sum of the individual voltages across the circuit, and
the total resistance of the circuit is the sum of the
individual resistances of each circuit load.
These relationships are summarized by the following
formulas.

𝑽𝒕𝒐𝒕𝒂𝒍 = 𝑽1 + 𝑽2 + 𝑽3 + . . . + 𝑽𝒏

𝑰𝒕𝒐𝒕𝒂𝒍 = 𝑰1 = 𝑰2 = 𝑰3 = . . . = 𝑰𝒏

𝑹𝒕𝒐𝒕𝒂𝒍 = 𝑹1 + 𝑹2 + 𝑹3 + . . . + 𝑹𝒏
EXAMPLE
Compute the individual values and the total values of the
voltage, the current and the resistance of the series circuit here.
STEP 1
Write down all the given in the series circuit using
Table Method.
 R1 R2 R3 TOTAL

Voltage (V) 𝟗𝑽
CURRENT (I)

RESISTANCE 𝟑Ω 10Ω 5Ω
(R)
STEP 2. How to calculate the total resistance?
The total resistance of the circuit is the sum of the individual resistances of
each circuit load. Therefore, we must get the sum of the individual
resistances in order to get the total resistance.

𝑹𝒕𝒐𝒕𝒂𝒍 = 𝑹1 + 𝑹2 + 𝑹3
𝑹𝒕𝒐𝒕𝒂𝒍 = 𝟑Ω+ 10Ω + 5Ω
𝑹𝒕𝒐𝒕𝒂𝒍 = 𝟏𝟖 Ω
Write down the total resistance in the Table

R1 R2 R3 TOTAL

Voltage (V) 𝟗𝑽
CURRENT (I)

RESISTANCE
(R)
𝟑Ω 10Ω 5Ω 18Ω
STEP 3. How to calculate the individual and total current?
By using the Ohm’s law formula 𝑽 = 𝑰𝑹 , the total current will be computed
by deriving the equation. Therefore, the total voltage divided by the total
resistance will be the total current. Because the total voltage is 9 V, you
can compute the total current as follows

𝑽 = 𝑰𝑹
𝑽 𝟗 𝑽
𝑰= = = 𝟎. 𝟓 𝑨
𝑹 𝟏𝟖Ω
Since the current is the same for all the components along the circuit,
write down the calculated total current in the table.

R1 R2 R3 TOTAL

Voltage (V) 𝟗𝑽
CURRENT (I)
𝟎. 𝟓 𝑨 𝟎. 𝟓 𝑨 𝟎. 𝟓 𝑨 𝟎. 𝟓 𝑨
RESISTANCE
(R)
𝟑Ω 10Ω 5Ω 18Ω
STEP 4. How to calculate the individual and total voltage?

Because the type of connection is a series circuit, I1 is 0.5 A, I2 is

0.5 A and I3 is 0.5 A. From these values, you have

𝑽 = 𝑰𝑹
𝑽𝟏 = 𝑰𝟏 𝑹𝟏
𝑽𝟏 = 𝟎. 𝟓 𝑨 (𝟑Ω)
𝑽𝟏 = 𝟏. 𝟓 𝑽
STEP 4. How to calculate the individual and total voltage?

Because the type of connection is a series circuit, I1 is 0.5 A, I2 is

0.5 A and I3 is 0.5 A. From these values, you have

𝑽 = 𝑰𝑹
𝑽𝟐 = 𝑰𝟐 𝑹𝟐
𝑽𝟐 = 𝟎. 𝟓 𝑨 (10Ω)
𝑽𝟐 = 𝟓 𝑽
STEP 4. How to calculate the individual and total voltage?

Because the type of connection is a series circuit, I1 is 0.5 A, I2 is

0.5 A and I3 is 0.5 A. From these values, you have

𝑽 = 𝑰𝑹
𝑽𝟑 = 𝑰𝟑 𝑹𝟑
𝑽𝟑 = 𝟎. 𝟓 𝑨 (5Ω)
𝑽𝟑 = 𝟐. 𝟓 𝑽
STEP 4. How to calculate the individual and total voltage?
Since the given total voltage is 9 V, the sum of the three
calculated voltage is equal to the given total voltage. You can
compute the total voltage as follow

𝑽𝒕𝒐𝒕𝒂𝒍 = 𝑽𝟏 + 𝑽𝟐 + 𝑽𝟑
𝑽𝒕𝒐𝒕𝒂𝒍 = 𝟏. 𝟓 𝑽 + 𝟓 𝑽 + 𝟐. 𝟓 𝑽
𝑽𝒕𝒐𝒕𝒂𝒍 = 𝟗 𝑽
Write down the three calculated voltage in the table

R1 R2 R3 TOTAL

Voltage (V) 𝟏. 𝟓 𝑽 𝟗𝑽
𝟓𝑽 𝟐. 𝟓𝑽
CURRENT (I)
𝟎. 𝟓 𝑨 𝟎. 𝟓 𝑨 𝟎. 𝟓 𝑨 𝟎. 𝟓 𝑨
RESISTANCE
(R)
𝟑Ω 10Ω 5Ω 18Ω
PARALLEL CIRCUIT
Parallel circuits use branches to allow current to pass through
more than one path, unlike in the series circuit.

The voltage between two points in the circuit does not depend
on the path taken; thus, the individual voltages in a parallel
circuit are the same as the total voltage.
PARALLEL CIRCUIT
However, unlike in the series circuit, the current in each load is not
the same as the total current in the circuit. The total current is the
sum of the individual currents across the resistors.

The reciprocal of the total resistance in this type of circuit is equal

to the sum of the reciprocals of the individual resistances. Always
remember that the total resistance is always less than the
individual resistances.
Here are the following formulas for a parallel circuit:

𝑽𝒕𝒐𝒕𝒂𝒍 = 𝑽𝟏 = 𝑽𝟐 = 𝑽𝟑 = . . . = 𝑽𝒏

𝑰𝒕𝒐𝒕𝒂𝒍 = 𝑰𝟏 + 𝑰𝟐 + 𝑰𝟑 + . . . + 𝑰𝒏
𝟏ൗ = 𝟏ൗ + 𝟏ൗ + 𝟏ൗ + . . . + 𝟏ൗ
𝑹𝒕𝒐𝒕𝒂𝒍 𝑹𝟏 𝑹𝟐 𝑹𝟑 𝑹𝒏
EXAMPLE
Compute the individual values and the total values of the
voltage, the current and the resistance of the parallel circuit
here.
STEP 1
Write down all the given in the parallel circuit using
Table Method.
 R1 R2 R3 TOTAL

Voltage (V) 15 𝑽
CURRENT (I)

RESISTANCE
(R)
7Ω 4Ω 2Ω
STEP 2. How to calculate the total resistance?
The total resistance of the circuit is computed as
follows:
Quotient and product of LCD
and the given resistors.

𝟏 𝟏 𝟏 𝟏 𝟖 +𝟏𝟒 +𝟐𝟖 𝟓𝟎 𝟓𝟔
= + + = = Ω = Ω= 𝟏. 𝟏𝟐Ω
𝑹𝒕𝒐𝒕𝒂𝒍 𝟕Ω 4Ω 2Ω 𝟓𝟔 𝟓𝟔 𝟓𝟎

Get the LCD of the 3 LCD of the 3 Reciprocal of the

denominators denominators total resistance
Write down the total resistance in the Table

R1 R2 R3 TOTAL

Voltage (V) 𝟏𝟓 𝑽
CURRENT (I)

RESISTANCE
(R)
7Ω 4Ω 2Ω 1.12Ω
27

STEP 3. How to compute the individual and total voltage?

Because the total voltage is 15 V and the resistors

are connected in parallel, then V1 is 15 V, V2 is 15 V
and V3 is also 15 V. Then the total voltage will be 15
V. The table will be:
 R1 R2 R3 TOTAL

Voltage (V) 𝟏𝟓 𝑽
𝟏𝟓 𝑽 𝟏𝟓 𝑽 𝟏𝟓 𝑽
CURRENT (I)

RESISTANCE
(R)
7Ω 4Ω 2Ω 1.12Ω
29

STEP 4. How to compute the individual and total current?

Because the type of connection is parallel circuit, V1 is 15 V, V2 is 15 V
and V3 is also 15 V. From these values, calculate the current using
Ohm’s Law Equation.
𝑽 = 𝑰𝑹
𝑽𝟏 𝟏𝟓 𝑽
𝑰𝟏 =
𝑹𝟏
=
𝟕Ω
= 𝟐. 𝟏𝟒 𝑨
30

STEP 4. How to compute the individual and total current?

Because the type of connection is parallel circuit, V1 is 15 V, V2 is 15 V
and V3 is also 15 V. From these values, calculate the current using
Ohm’s Law Equation.
𝑽 = 𝑰𝑹
𝑽𝟐 𝟏𝟓 𝑽
𝑰𝟐 =
𝑹𝟐
=
4Ω
= 𝟑. 𝟕𝟓 𝑨
31

STEP 4. How to compute the individual and total current?

Because the type of connection is parallel circuit, V1 is 15 V, V2 is 15 V
and V3 is also 15 V. From these values, calculate the current using
Ohm’s Law Equation.
𝑽 = 𝑰𝑹
𝑽𝟑 𝟏𝟓 𝑽
𝑰𝟑 =
𝑹𝟑
=
2Ω
= 𝟕. 𝟓 𝑨
32

The sum of the three calculated current is equivalent to the total

current of the given circuit. The total current is computed as
follows:

𝑰𝒕𝒐𝒕𝒂𝒍 = 𝑰𝟏 + 𝑰𝟐 + 𝑰𝟑
𝑰𝒕𝒐𝒕𝒂𝒍 = 𝟐. 𝟏𝟒 𝑨 + 𝟑. 𝟕𝟓 𝑨 + 𝟕. 𝟓 𝑨
𝑰𝒕𝒐𝒕𝒂𝒍 = 𝟏𝟑. 𝟑𝟗 𝑨
33

The total current can also be computed using the Ohm’s Law
Equation, where:

𝑽 = 𝑰𝑹
𝑽𝒕𝒐𝒕𝒂𝒍 𝟏𝟓 𝑽
𝑰𝒕𝒐𝒕𝒂𝒍 =
𝑹𝒕𝒐𝒕𝒂𝒍
=
𝟏. 𝟏𝟐𝑽
= 𝟏𝟑. 𝟑𝟗 𝑨
Write down the individual and total current in the table.

R1 R2 R3 TOTAL

Voltage (V) 𝟏𝟓 𝑽
𝟏𝟓 𝑽 𝟏𝟓 𝑽 𝟏𝟓 𝑽
CURRENT (I)
𝟐. 𝟏𝟒 𝑨 𝟑. 𝟕𝟓𝑨 𝟕. 𝟓𝑨 𝟏𝟑. 𝟑𝟗𝑨
RESISTANCE
(R)
7Ω 4Ω 2Ω 1.12Ω
 R1 R2 R3 TOTAL

Voltage (V) 𝟗𝑽
CURRENT (I)

RESISTANCE 𝟑Ω 10Ω 5Ω
(R)