Southern Luzon State University
College of Engineering
Computer Engineering Department
ECE00 - Basic Electronics (Laboratory)
Activity 6: inductors
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1.1 Introduction
The Inductor: The inductor can best be described as electrical momentum (momentum is the
power a moving object has). In our water pipe analogy, the inductor can be thought of as a very long
hose wrapped around itself many times as shown here:
Since the hose is long it contains many gallons of water. When pressure is applied to one end of
the hose with a plunger the water would not start to move instantly, it would take time to get the water
moving. After a while the water would start to move and pick up speed. (This is also similar to a long
freight train, which takes more than a mile to get to full speed or to stop). The speed would increase
until limited by the friction (resistance) of the hose as normal. If you try to instantly stop the water from
moving by holding the plunger, the momentum of the water would create a large negative pressure
(suction) that would pull the plunger from your hands.
Inductors are made by coiling a wire, hence they are also called coils. From the above analogy it
should be apparent that a coiled hose will pass DC (a constant or unchanging current) with only the
resistance of the hose, which in electronics will be very low since the hose is a wire. If the pressure on
the plunger is alternated (pushed, then pulled) fast enough then the water in the coil will never start
moving and the AC (constantly changing current) will be blocked. Coils in electronics follow these same
principles - a coil will pass DC and block AC.
Recall from above that a capacitor will block DC but pass AC. When determining the response of
a circuit to DC, inductors are treated as closed switches and capacitors are treated as open switches. For
the AC response, the values of the inductors and capacitors must be considered along with the rate at
which the current alternates (called the frequency). For DC changes to the circuit (called transients),
such as closing the switch to connect a battery to capacitor circuit, the circuit response is initially AC and
then reverts to DC.
The inductance is expressed in henrys (H, named after Joseph Henry who developed
electromagnetic induction at the same time as Faraday), or more commonly in millihenrys (mH,
thousandths of a henry) or microhenrys (μH, millionths of a henry). A typical inductor and its symbol are
shown below:
Inductors and Transformers: Our water pipe analogy we have been using all this time is not
entirely accurate. Electric current is not the same as water. It is a flow of sub-atomic particles called
electrons that not only have electric properties but also magnetic properties; in the water pipe analogy
you would have to think of the water as containing millions of very small magnets. Inductance expresses
the magnetic effects between electrons flowing in the wire of a coil.
The number of turns (windings), diameter, and length of the coil affect the inductance, the
thickness of the wire does not. The material inside the coil also affects the inductance; if you wrap the
coil wire around an iron bar (which has strong magnetic properties) then the magnetic effects are
increased and the inductance is increased. This does not apply to capacitors, which store electric charge
in an electric field, not a magnetic field.
If you wrap two wires from different circuits around different ends of an iron bar, then a current
flowing through the wire from the first circuit will magnetically create a current in the wire from the
second circuit! If the second coil has twice as many turns (more magnetic linkage) as the first coil, then
the second coil will have twice the voltage but half the current as the first coil. A device like this is called
a transformer.
The magnetic field created in an iron bar by an electric current in the coil around it can be
harnessed if the bar is allowed to rotate - it is a motor. It could be used to drive the wheels of a car, for
example. The reverse is also true, if a magnet within a coil is rotating then an electric current is created
in the coil - a generator. These two statements may not seem important to you at first but they are
actually the foundation of our present society. Nearly all of the electricity used in our world is produced
at enormous generators driven by steam or water pressure. Wires are used to efficiently transport this
energy to homes and businesses where it is used. Motors convert the electricity back into mechanical
form to drive machinery and appliances.
It must be remembered that all of the inductance properties discussed here for coils and
transformers only apply to AC (alternating current). For DC, inductors act as wires with no special
properties and transformers are just two separate, unconnected wires.
1.2 Objective
● To use easyEDA in simulating electronic circuit with inductors.
● To use inductors as transformers in electronic circuits.
● To manipulate various schematic diagram in determining the effects of inductors in a circuit.
1.3 Problem
Create a circuit diagram on your easyEDA with the given situations below.
1. Magnetic Bridge:
2. Alarm: Trip wire will be replaced by a switch.
3. Siren
4. Electronic Noisemaker
#1 SS
#2SS
#3 SS
#4 SS
1.4 Follow up Questions:
1. What are the roles of inductors in DC and AC circuit?
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2. What are the practical applications (at least 2) of inductors as transformers that you can say that you
already use? Discuss each
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3. What are your insight with the activities so far? (All of the 6 activity)
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1.5 Conclusion:
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Note: use pdf file format only in submitting every activity.
