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Name: _______________
Date: ________________
Chapter 13 - Electrical Quantities in Circuits
13.1 - Circuits and Circuit Diagrams
A circuit diagram is used to draw an electric circuit, using symbols to represent the various
components.
Component:
Description:
Circuit diagram symbol:
load
electrical device that converts electrical
energy into another form of energy (e.g., a
light bulb, fan, motor)
control device that allows you to safely
open or close a circuit
lamp:
switch
energy source
provides the electrical energy (e.g., a
battery)
motor:
open:
closed:
electric cell:
3-cell battery:
conducting wire
allows electrons to flow easily through the
circuit
In a series circuit, loads are connected so that there is only ___________ path for electrons to flow.
In a parallel circuit, loads are connected so that there are ___________ or more paths for electrons
to flow.
**Do questions #1,2,4,5 on page 554**
13.3 - Electric Current
Electric current (I) is the rate of electron flow at any point in a circuit. It is measured in
________________ (A) by an ammeter. An ammeter is connected in series with the load to
measure the current flowing through the load.
If there is too much current flowing through a circuit, it can damage electrical devices and cause an
electrical fire. Circuit ________________ (or fuses, in older homes) stop the flow if there is too much
current.
**Do questions #3,4 on page 557**
13.5 - Potential Difference
Potential difference or voltage (V) is the difference in electric potential energy measured at two
points. It is measured in ________________ (V) by a voltmeter. A voltmeter is connected in parallel
with the load to measure the potential difference across the load.
**Do questions #3,4 on page 561**
13.7 - Resistance in Circuits
Electrical resistance (R) is the ability of a material to oppose (resist) the flow of electric current. It is
measured in ________________ (Ω) by an ohmmeter. An ohmmeter is connected in parallel with a
load.
All materials have internal resistance. The greater the resistance, the less current flows through, and
the more electrical energy is converted into thermal energy (heat).
Factors affecting internal resistance:
-type of material (silver has ________________ internal resistance than copper)
-cross-sectional area (the thicker the wire, the ________________ the internal resistance)
-length (the longer the wire, the ________________ the internal resistance)
-temperature (the higher the temperature, the ________________ the internal resistance)
A resistor is a device that ________________ the flow of electric current. For example, dimmer
switches and volume controls on a stereo control the amount of current flowing by changing the
resistance in a circuit.
**Do questions #4,5,6,7 on page 566**
13.9 - Relating Current, Voltage, and Resistance
Ohm's Law describes the relationship between current (I), potential difference (V), and resistance (R)
V = IR
This can be rearranged to:
R=V÷I
or
I=V÷R
*See sample problems on pages 568-569*
**Do questions #2,4,5,6,7 on page 570*
13.10 - How Series and Parallel Circuits Differ
When more than 1 load is connected in series in a circuit:
-the greater the resistance in the circuit and the less current flowing through each load
-the lower the potential difference across each load
Vload = Vsource ÷ the number of loads
When more than 1 load is connected in parallel in a circuit:
-the total current is split into the different pathways of the circuit
Iload = Isource ÷ the number of (identical) loads
-the total resistance is less because electrons only flow through one load in any pathway, so
Vload = Vsource
In summary:
Quantity:
Series circuits:
Parallel circuits:
total resistance of circuit (RT)
increases
decreases
current through loads (Iload)
Isource decreases as more loads
are added
voltage across loads (Vload)
Vsource splits based on the
number of loads
Isource splits among loads based
on the number of branches in
parallel
voltage of each parallel branch
is the same as Vsource
**Do questions #4,5,6,7 on page 575**
Other circuit symbols:
Component:
ammeter
voltmeter
Symbol:
Component:
ohmmeter
resistor
Symbol: