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