Learn about electricity, circuits,

1. Lesson 6: Electricity
Technology 3º ESO

2. Index
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What is electricity
Electrical magnitudes
Ohms law
Measuring with a multimeter
Electric circuits: Elements
Electric symbols
Types of circuits
Electric machines

3. What is electricity?
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Electricity is a form of energy
It has its origin in the electrical
charges existing in the atoms
(electrons and protons), which
strongly interact
Electricity can be natural, such
as ligthning or artificial (electric
circuits)
As a form of energy, it is easy
to produce and transform.
Index

4. ELECTRIC MAGNITUDES
Magnitude
Definition
Units
Expression
Voltage,
(tension)
Energy given to the
charges to move
them
V (volts)
V=I·R
Resistance
Difficulty to be
passed by electricity
Ω(ohm)
R= ρ·l/s2
Intensity
Charge passing
through a conductor
in a second
A (amp)
I=Q / t(s)
Power
Energy produced (or
lost) by the current in
a time unit
W
(watt)
P=V·I
PL=R·I2
Index

5. Ohm’s law
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Ohm’s law says that the
tension is equal to the
product of the intensity
and the resistance
V=R·I
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This is equivalent to:
I=V/R ↔R=V/I
Index

6. Electric circuits and their
elements
An electric circuit is a closed
path where the charges flow
between to points with
different electric tension
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We use electric circuits to
transport and transform
energy
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An electric circuits needs at
least
1.
A power supply
2.
A conductor
3.
A receiver
It is also important to include
control elements
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Index

7. Power suppliers
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1.
2.
A power supply gives
energy to the charges so
that they flow trough the
circuit
There are different types
of suppliers
Chemical: batteries DC
Mechanical: dynamos DC
and alternators AC

8. Conductors
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A conductor is an
element where the
charges flow without a
significant resistance
They are normally
wires: several long and
thin copper (or
aluminum) conductors
covered by an insulating
plastic layer

9. Receivers
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1.
2.
3.
4.
5.
Receivers transform electricity into a useful form of energy so that we
make the circuit profitable. They can convert electricity into:
Ligth: lamps
Movement: motors
Heat: resistances
Sound: speakers
etc

10. Control elements
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Control elements let us
stop or allow the flow of
charges (switch) or
change the way of the
electricity through the
circuit (conmuter)
Index

11. Electric symbols
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An electric symbol is
a picture which
represents a circuit
or an element of it
They make it easier
to represent and
understand circuits
Index

12. Electric machines
 Many
essential devices work or help us
to control electricity
 Transformer
 Motor
 Dynamos or alternators
 Relay
Index

13. Transformers
Transformers change (raise or lower the)
tension of the alternating current
They are formed by a square core with two
coils (copper wires), primary (N1 turns ,
V1 and I1) and the secondary.
The alternating current induces a magnetic
flux wich travels trough the iron core and
induces a current I2 with a voltage V2 in
the secondary coil of N2 turns. This
equations are satisfied
P1=P2 ↔ V1·I1=V2·I2
V1/N1=V2/N2 ↔ V1·N2=V2·N1
I1·N1=I2·N2

14. Motors
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Motors can be AC or
DC. They are both
based on magnetic
fields. A current flows
trough a coil in the rotor /
stator. The stator / rotor
is a magnet. Due to the
variation of the magnetic
field flow caused by the
electric current

15. Dynamos / alternators
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Dynamos (DC) or alternators (AC) are like motors
which generate DC or AC current when the rotor is
moved inside the stator. The variation of the magnetic
field due to the rotation of a magnet induces an electric
current in the stator.

16. Relays
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1.
2.
A Relay is a swith controlled by an
electromagnet.
An electromagnet is a coiled
conductor wire where the current
flows creating a magnetic field.
The magnetic field makes the swith
change its position due to magnetic
atraction
When current stops, the magnetic
field dissapears and the switch
returns to its original position due to
a spring.
Relays have two independent
circuits:
the control circuit: Activates the
electromagnet
The power circuit, which is
controlled by the switch
Index