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Inductors
Inductance
• Electrons in motion create electromagnetic fields – Recall from previous section that electrons in
motion also create an electrostatic field
• The electromagnetic field can be intensified by making a loop in the wire
• A device which creates an electromagnetic field is called an inductor
Inductors
Schematic symbol for inductor or coil
Inductance
• The unit of measure of inductance is henry• The inductor is an electromagnet• One use of the inductor is in relays to operate
a switch• Another use is in the construction of electric
motors
Relays
Contacts
Relays
M
12 volts
760 volts
Relays
M
Relays
M
Inductors
Inductors
Inductors
• Three factors affecting inductance– Nature of the coil
• Size• Diameter of conductor• Number of turns• Length
– Current flow– Presence of materials within the magnetic field
Variable Inductor
Inductors
• When current is turned off from electromagnet, the electromagnetic field collapses back to the coil
• There is a charge or current present on the inductor
• Electromagnetic energy is stored in inductors• Inductors are used to convert AC to DC
Inductors
0 volts
10 volts
Time
“on” “off” “on” “off”
Capacitor Inductor
Inductors
• Energy is expended in forming electromagnetic field
• Inductors resist current flow – electrons resist flow
• Impedance is reluctance in a coil• Three factors affecting inductance also affect
impedance
Transformers
• Transformers are constructed from two inductors or coils in close proximity to one another
• Just like capacitors, current can be induced to flow in the secondary coil if enough current flows through the primary
• Transformers are used to increase or decrease current flow and/or voltage
Transformers
Primary Secondary
Transformers
• Step up transformers have more turns in the secondary coil and increase output
• Step down transformers have fewer turns in the secondary and decrease output
• Isolating transformers have same number of turns in both coils and neither decrease nor increase output – but isolate two segments of a circuit
Transformers