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Comparing Resistance, Voltage and Current across Loads in
Series and Parallel Circuits
***Recall***
 Current (I) is the amount of charge (coulombs) that passes a point at any second. Current is measured
in amperes (A). Charge (Q) is measured in coulombs (C)
o Example: If there are 10A in a circuit, that means there are 10C of charge passing every second
 Potential difference (voltage/ V) is the difference in the amount of energy per coulomb of charge,
before and after a load (Joules/coulomb = V). Measured in parallel.
o Example: If a battery has 10V, then each coulomb that leaves the battery has 10J of energy in it
and if a bulb in that circuit has a potential difference of 5V then there is a difference of
5J/coulomb from before it reaches the bulb till after it leaves the bulb.
Series Circuits
 _____________________________________________________________________
Facts About Series Circuits
 When batteries are connected in series, the electrons that pass through receive the sum of the two
electric potentials (voltage)
 As more loads are added in series, the _____________________________________________ and the
_____________________________________________________________________.
 Batteries in a ____________________________________ than batteries in a similar parallel circuit.
 Electric loads in a _________________________________ than electric loads in a similar parallel
circuit.
Parallel Circuits
If components of an electric circuit are in different pathways (electrons pass through one circuit or another)
the components are said to be in parallel with each other.
Facts About Parallel Circuits

Electrons that flow through a Battery in parallel only receive the energy (electric potential) of one
battery. Therefore _________________________________________ then in a similar series circuit.

When electric loads are found in parallel, the electrons have the choice to move through one load or the
other. Therefore they do not need to share half their energy with both electric loads. They are able to
donate all of their energy to one electric load. Therefore loads in parallel use _____________________
than a similar series circuit.
Quantity
Series Circuit
Parallel Circuit
Equations:
Series
Parallel
Current (I)
Voltage (V)
Resistance ()
Calculating Using Drawings
Legend:
It = amount of current flowing through the source
I1 = amount of current flowing through bulb #1
I2 = amount of current flowing through bulb #2
I3 = amount of current flowing through bulb #3
Vt =potential difference across the source
V1 =potential difference across bulb #1
V2 = potential difference across bulb #2
V3 = potential difference across bulb #3
Req= The total resistance equivalent
R1 = Resistance of resistor 1
R2 = Resistance of resistor 2
R3 = Resistance of resistor 3
Part A:
Consider the following circuit:
A) Is it connected in series or in parallel?_______________________________
B) If It = 50 mA I1=_________________
I2=___________________
I3= ____________________
C) If Vt= 9V
V1=________________
V2=__________________
V3= ___________________
D) If Req =
R1=_________________
R2=___________________
PART B:
Consider the following circuit:
A) Is it connected in series or in parallel?_______________________________
B) If It = 50 mA I1=_________________
I2=___________________
I3= ____________________
C) If Vt= 9V
V1=________________
V2=__________________
V3= ___________________
D) If Req =
R1=_________________
R2=___________________
PART C:
a) Draw a schematic diagram illustrating a 6V battery, three bulbs, bulbs 1 and 2 are wired in series with
each other and bulb 3 is in parallel with bulbs 1 and 2.
b) If the voltage is 6V across bulb 3 and bulb 1 is 4V, what is the voltage across bulb 2?
Homework Questions:
1. Compare the total resistance of loads connected in series with those connected in parallel.
2. What would happen if you connected too many bulbs into a series circuit (voltage and brightness)?
3. The total resistance in the circuit is 25 and the voltage drop is 6.0V. Calculate the current in this series
circuit.
4. A parallel circuit has four identical lamps. The potential difference across the energy source is 48V. The
total resistance is 12. Calculate the current in each lamp.
5. A series circuit contains four identical lamps. The voltage across the energy source is 96V. Calculate the
voltage across each lamp.
6. If the total voltage drop for a parallel circuit with 3 lamps is 120V and the total resistance is 10,
calculate the current and the voltage through each lamp.
7. A battery powered set of 4 patio lanterns is connected in series. An ammeter measures the current of the
battery at 0.75A. The total resistance of the circuit is 52. What is the voltage drop across the battery?
What is the voltage drop across each bulb?