The document explains parallel circuits, which allow electricity to flow through multiple paths, ensuring current continues to flow even if one path is broken. It outlines key principles, including that the voltage is equal across all components, total current is the sum of individual branch currents, and total resistance is less than any individual resistance. It provides the formula for calculating total resistance in a parallel circuit and emphasizes the importance of these principles in understanding electrical circuits.

2. ELECTRICAL CIRCUITS
All you need to be an inventor is a
good imagination and a pile of
junk.
-Thomas Edison

3. Parallel Circuits
A parallel circuit is one that has two or more
paths for the electricity to flow, the loads
are parallel to each other.
If the loads in this circuit were light bulbs
and one blew out, there is still current
flowing to the others because they are still
in a direct path from the negative to positive
terminals of the battery.

4. Three principles regarding
parallel circuits:
1) Voltage
- Voltage is equal across all components in a
parallel circuit.
2) Current:
- The total circuit current is equal to the
sum of the individual branch currents.
3) Resistance
- Individual resistances diminish to equal a smaller
total resistance rather than add to make the total.

5. Example of a Parallel Circuit

6. Georg Simon Ohm (1787-1854)

7. Ohm’s Law
I = Current (Amperes) (amps)
V = Voltage (Volts)
R = Resistance (ohms)
I = V / R

8. UNDERSTANDING & CALCULATING
PARALLEL CIRCUITS
For one, the total resistance of a Parallel Circuit is
NOT equal to the sum of the resistors (like in a series
circuit). The total resistance in a parallel circuit is
always less than any of the branch resistances.
Adding more parallel resistances to the paths causes
the total resistance in the circuit to decrease. As you
add more and more branches to the circuit the total
current will increase because Ohm's Law states that
the lower the resistance, the higher the current.

9. UNDERSTANDING & CALCULATING
PARALLEL CIRCUITS

10. Voltage in Parallel Circuits
The first principle to understand about
parallel circuits is that the voltage is equal
across all components in the circuit. This is
because there are only two sets of
electrically common points in a parallel
circuit, and the voltage measured between
sets of common points must always be the
same at any given time.

11. "The sum of the currents through each
path is equal to the total current that
flows from the source."
If one path is drawing 1 amp and the
other is drawing 1 amp then the total is
2 amps at the source. If there are 4
branches in this same 2 amp circuit,
then one path may draw 1/4A (.25A),
the next 1/4A (.25), the next 1/2A (.5A)
and the last 1A.

12. "The sum of the currents through each
path is equal to the total current that
flows from the source."

13. "You can find TOTAL RESISTANCE in a
Parallel circuit with the following
formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 + ... "
Before we get into the calculations,
remember that: "The total resistance of
a parallel circuit is NOT equal to the sum
of the resistors (like in a series circuit).

14. "You can find TOTAL RESISTANCE in a
Parallel circuit with the following
formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 + ... "

15. "You can find TOTAL RESISTANCE in a
Parallel circuit with the following
formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 + ... "
 Voltage = 12V
 R1 = 4 Ohm
 R2 = 4 Ohm
 R3 = 2 Ohm
Remember that "Rt" means Total resistance
of the circuit.
R1, R2, etc. are Resistor one, Resistor two,
etc.

16. "You can find TOTAL RESISTANCE in a
Parallel circuit with the following
formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 + ... "
Now we will apply the formula
above to this example:
1 1 1 1
— = — + — + —
Rt R1 R2 R3

17. "You can find TOTAL RESISTANCE in a
Parallel circuit with the following
formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 + ... "
Therefore:
1 1 1 1
— = — + — + —
Rt 4 4 2

18. "You can find TOTAL RESISTANCE in a
Parallel circuit with the following
formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 + ... "
It is easiest to change the fractions into decimal
numbers (example 1 divide by 4 equals .25):
1/Rt = .25 + .25 + .5
1/Rt = 1
Now you have to get rid of the 1 on the left side
so...
Rt = 1/1
Rt = 1 Ohms

19. What if one of the parallel paths
is broken?
 Even if one of the parallel paths is broken, current will
continue to flow in all the other paths.
 The best way to illustrate this is also with a string of light
bulbs in parallel. If one is burnt out, the others stay lit.

20. Three Rules of Parallel Circuits
In summary, a parallel circuit is defined as one where all
components are connected between the same set of
electrically common points. Another way of saying this is that
all components are connected across each other’s terminals.
From this definition, three rules of parallel circuits follow:
 All components share the same voltage.
 Resistances diminish to equal a smaller, total resistance.
 Branch currents add to equal a larger, total current.