ELECTRIC CIRCUITS

1
Chapter 35 ELECTRIC CIRCUITS
2

• What you will learn
• You will distinguish between parallel and series
  circuits and series-parallel combinations and
  solve problems dealing with them.
• You will explain the function of fuses, circuit
  breakers, and ground-fault interrupters (GFIs)
  and describe ammeters and voltmeters.
•  

3

• Why its important
• Electrical circuits are the basis of every
  electrical device, from electric lights to
  microwave ovens to computers. Understanding
  circuits helps you to use them, and to use them
  safely.
•     

4
Chapter 23 Series and Parallel Circuits
I. A Battery and a Bulb (35.1) A. Circuit- A
complete pathway for electrons to flow 1. Flow
of electrons like flow of water in a closed
system of pipes a. The battery would be
analogous to the pump b. Wires analogous to
the water pipes
5
B. The water flows through the pump and the
electrons flow through the battery
6
II. Electric Circuits (35.2) A. Electric
Circuit- any path along which electrons can
flow 1. Must be a complete circuit with no
gaps 2. Gap usually provided by electric
switch
7
B. Most circuits have more than one device that
receives electrical energy. Devices can be
connected in a circuit in one of two ways, series
or parallel.
8
III. Series Circuits (35.2) A. Electric current
has but a single pathway through a series
circuit. Current is the same through each
electrical device in the circuit  
9
B. The total resistance to current in the circuit
is the sum of the individual resistances along
the circuit path R RA RB ..  
10
C. The current in the circuit is equal to the
voltage supplied by the source divided by the
total resistance of the circuit (in accord with
Ohms law)  
11
D. The total voltage impressed across a series
circuit divides among the electrical devices in
the circuit so that the sum of the voltage
drops across each device is equal to the total
voltage supplied by the source.  

12
E. The voltage drop across each device is
proportional to its resistance. This follows
from the fact that more energy is wasted as heat
when a current passes through a high-resistance
device than when the same current passes through
a device offering little resistance.  

13
QUESTION What happens to current in other
lamps if one lamp in a series circuit burns out?
ANSWER The path to the current will break and
current will cease. All lamps will go out
14
QUESTION What happens to the light
intensity of each lamp in a series circuit when
more lamps are added to the circuit?
ANSWER This results in greater circuit
resistance. This decreases the current in the
circuit and therefore in each lamp, which causes
dimming of the lamps. Energy is divided among
more lamps
15
QUESTION What is the current through
this series circuit?
ANSWER Use the equation for Ohms law and solve.
First calculate the total resistance.
16
QUESTION In this simple series circuit, a
small electronic component is
connected before the
LED light
bulb. What is this and why do
you think they use it?
ANSWER The component is
a resistor. It produces
a
voltage drop in accordance
to Ohms law
17
IV. Parallel Circuit (35.4) A. Each device
connects the same two points A and B of the
circuit. The voltage is therefore the same
across each device  
18
 B. The total current in the circuit divides
among the parallel branches. Because the voltage
across each branch is the same, the amount of
current in each branch is inversely proportional
to the resistance of the branch 
Remember that the voltage is the same across each
of the branches
19
C. The total current in the circuit equals the
sum of the currents in its parallel branches  

Where IA, IB, IC are currents through the
branches and I is the total current
20
D. As the number of parallel branches is
increased, the overall resistance of the circuit
is decreased (just as more check-out cashiers at
a supermarket decreases people-flow resistance).
With each added parallel path,the overall circuit
resistance is lowered. This means the overall
resistance of the circuit is less than the
resistance of any one of the branches. 

21
QUESTION What happens to the current in
other lamps if one of the lamps in a parallel
circuit burns out?
ANSWER In one lamps burns out, the other lamps
will be unaffected. The current in any other
single branch is unchanged. The total current in
the overall circuit is decreased by an amount
equal to the current drawn by the lamp in
question.
22
QUESTION What happens to the light
intensity of
each lamp in a
parallel circuit when more
lamps are added in
parallel
to the circuit
ANSWER The light intensity for each lamp is
unchanged. Only the total resistance and the
total current in the total circuit changes. No
changes in any individual branch in the circuit
occur
23
V. Schematic Diagrams (35.5) A. Schematic
diagram- simple diagrams to represent electrical
circuits.
1. Symbols used to represent certain circuit
elements 2. Circuit diagrams (schematics) show
electrical connections, not the physical layout
24
3. Common Symbols
25
B. Examples of Series and Parallel circuits
26
VI. Combining Resistors in a Compound Circuit
(35.6) A. Sometimes it is useful to know the
equivalent resistance of a circuit that
has several resistors in its network 1.
Equivalent resistance- value of the single
resistor that would comprise the same load to
the battery or power source 2. Calculate
using the rules for adding resistors in series
and parallel
27
B. Series circuits-
28
C. Parallel circuits-
29
VII. Parallel Circuits and Overloading (35.7) A.
When add more devices (pathways) in house, the
combined resistance is lowered in the
circuit 1. Therefore, greater amount of
current occurs 2. Can overload circuit and
may result in heat (fire) B. Connect fuses in
series along supply line to protect (fuse or
circuit breaker prevents overloading)
30

•  Ammeters and Voltmeters
• Ammeter
• An ammeter measures current in any branch or
  part of a circuit
• It does not change the current in the circuit
  

31

• Voltmeter
• Used to measure voltage drop across some part of
  a circuit
• Has very high resistance so that is causes the
  smallest possible change in current or voltages
  in the circuit
•  

32
conventional current flow theory an older theory
stating that electric current flows from the more
positive source to the more negative source
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)