This document discusses parallel circuits. It defines parallel circuits as having multiple paths for current to flow and that the voltage is the same across each component. The total resistance of a parallel circuit is smaller than its branches because the overall conductance is the sum of the individual conductances. The current divider rule is used to calculate the current through each resistor in a parallel circuit.

3.  Definition of Parallel Circuits.
 Total Resistance of Parallel Circuits.

4.  Why Total Resistance of Parallel Circuits is
smaller?

5. Voltage is always the same across parallel
elements.
V1 = V2 = E
The voltage across resistor 1 equals the voltage
across resistor 2, and both equal the voltage
supplies by the source.

6.  Why Voltage is Constant in Parallel Circuits?
Ohms Law, V=IR

7. The current divider rule (CDR) is used to find
the current through a resistor in a parallel
circuit.
General points:
 For two parallel elements of equal value, the
current will divide equally.
 For parallel elements with different values, the
smaller the resistance, the greater the share of
input current.
 For parallel elements of different values, the
current will split with a ratio equal to the inverse of
their resistor values

8. T
x
T
x I
R
R
I 

9. A Parallel circuit has certain characteristics and basic rules:
• A parallel circuit has two or more paths for current to flow through.
• Voltage is the same across each component of the parallel circuit.
• The sum of the currents through each path is equal to the total current that flows from the
source.
• You can find total resistance in a Parallel circuit with the following formula:
1/Rt = 1/R1 + 1/R2 + 1/R3 +...
• If one of the parallel paths is broken, current will continue to flow in all the other paths.

10. WHY WE USE CDR? :
• To find the current through each resistors(parallel).
• To find the polarity of each branch current.
T
x
T
x I
R
R
I 

11. 𝐼 𝑒𝑛𝑡𝑒𝑟𝑖𝑛𝑔 = 𝐼𝑙𝑒𝑎𝑣𝑖𝑙𝑛𝑔

12.  Conductance is the measure of the amount
of electrical current a material can carry or
it's ability to carry a current.
 Conductance is an expression of ease of
how current flows through a material .

13. General Points:
 Conductance is inverse of resistivity
 It helps to analyze property of a material
 Unit: mho or Siemens per meter (S/m)

14. G= 1/R
For a parallel circuit,
the total conductance in a parallel circuit is equal to the sum of
the individual conductance:

16. Electric power is the rate, per unit time,
at which electrical energy is transferred
by an electric circuit. The SI unit of
power is the watt, one joule per second

17. P= work done per unit time = VQ/t= VI
 P=VI=I2R=V2/R

18. Series Circuit
 Electrons only have
one path to flow
through.
Parallel Circuit
• There are MULTIPLE
paths for the current
to flow through.

19. Advantages
 The more devices (resistors) in a parallel circuit,
does not decrease the current (does not dim
bulbs).
 If one resistor breaks (a bulb goes out) the rest
do not.
Problems
 Current doesn’t stay the same for entire circuit
◦ So energy is used up quicker
◦ So the total current increases = faster electrons = hotter
wire = fire?

20. Parallel
 Most things are wired in parallel
 Because of the fact that the more you plug in,
the intensity doesn’t decrease.
 Of course, this also increases the risk of fire
 This is why homes have fuses or circuit
breakers. They turn off everything in the
circuit when current moves too fast.

21. Series Parallel
Voltage (V) Vtot = V1 + V2 +
V3…
Vtot = V1 = V2 = …
Current (I) Itot=I1=I2=I3 Itot = I1 + I2 + …
Resistance (R) Req = R1+R2+ R3… 1/Req=1/R1+1/R2+1/
R3

22. Car system:
The electrical system on a car is essentially a parallel
system.
Parallel computer bus connections
The bus connectors are connected in parallel with
common connections to the power supply, address
and data buses, control signals, and ground.

23. House wiring:
Except in some very special circumstances the basic
wiring of a house is done in a parallel configuration.
Each parallel branch, however, can have a
combination of parallel and series elements.
Each branch receives a full 120 V or 208 V, with the
current determined by the applied load.