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3º ESO - UNIT 4: ELECTRIC AND ELECTRONIC CIRCUITS

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Moisés Llorente Santos

on 10 April 2016

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Transcript of 3º ESO - UNIT 4: ELECTRIC AND ELECTRONIC CIRCUITS

STARTING QUESTIONS (5 groups)
Which particles are atoms made of?
Atoms are made of:
How are forces between those particles?
1. Repulsion forces:
Why does electric current happen?
UNIT 4: ELECTRIC AND ELECTRONIC CIRCUITS

Which particles are atoms made of? (5p)
How is the charge of these particles? (5p)
Why does electric current happen? (5p)
+
Neutrons, with neutral charge.
Protons, with positive (+) charge.
Electrons, with negative (-) charge, rotating around the nucleus.
N
N
+
-
What's the total charge of this atom?
-
+
+
-
-
2. Attraction forces:
+
-
Particles
with the same
charge are
repelled
(try to keep them away)
Particles
with different charge
are
attracted
(try to keep them together)
Imagine two close atoms, as follows:
+
N
N
+
-
-
+
N
N
+
-
neutral
positive
positive
neutral
The free electrons (-) orbitting around the nucleus are attracted by the positive (+) charge of the adjacent atom, and may jump to it.
If this jump happens, the atom that gets the electron will become neutral.
-
As a result of this movement of electrons, we have an
electric current
through certain materials.
Why does electric current happen?
+
N
N
+
-
-
+
N
N
+
-
+
N
N
+
-
+
N
N
+
-
+
N
N
+
-
+
N
N
+
-
-
-
-
-
-
-
direction of the electric current
Do all materials conduct electricity? (5p)
Do all materials conduct electricity?
The answer is NO
Not all materials allow electric currents to flow through them. It depends on the atomic structure of materials (quantity of free electrons and strength of links between them ant the atoms).
There are 3 main groups of materials (page 130):
CONDUCTORS
Allow electric currents to pass through them.
Lots of free electrons and weak links between them and the atoms.
All metals are good conductors.
INSULATORS
Don't allow electric currents to pass through them.
Little free electrons and strong links between them and the atoms.
Wood, plastics and air are insulators.
SEMICONDUCTORS
Have properties which are intemediate between conductors and insulators.
Silicon and germanium are good examples.
Very important materials in electronics (to make chips)
(neutrons and protons form the nucleus)
How does a battery work?
What's the difference between electricity and electronics? (5p)
An atom that is not neutral is called an
ion.
Moisés Llorente
Colegio Madrigal (Fuenlabrada)
Technology, progamming and robotics 3º ESO

3. Variables of direct current (page 79)
Voltage (or tension):
Is the energy that a battery or generator can provide for each electron. It is measured in volts (V).
Electric Current:
Is the charge, or number of electrons, that flows through conductor per second. It is measured in amperes (A).
Electrical resistance:
Is a measure of the degree to which the material opposes an electric current flowing through it. It is measured in ohms (Ω).
Insulators have very high levels of resistance, whereas metals have hardly any electrical resistance.
WHAT'S NECESSARY TO ALLOW AN ELECTRIC CURRENT TO FLOW THROUGH A CIRCUIT?
We need...
A
generator
to provide energy (a battery)
A
conductor
to provide the current a path
A
receiver
to consum/transform the energy
COMPONENTS OF AN ELECTRIC CIRCUIT
GENERATORS
RECEIVERS
CONTROL ELEMENTS
PROTECTION ELEMENTS
GENERATORS:
Provide the necessary energy for electrons to circulate.
NO GENERATOR
NO CIRCUIT
Examples of generators?
RECEIVERS:
transform electric energy into useable energy.
Types:
Light bulb:
produces light.
Motor:
transforms electricity into movement.
Resistor:
transforms electricity into heat.
Bell:
transforms electricity into sound.
CONTROL ELEMENTS:
help us to control the flow of the electric current, directing or interrupting it.
Types:
Switch:
allows a current to flow permanently or to be interrupted.
Push button:
allows the current to flow through it only when pressure is mantained.
Circuit switch:
directs the current through a branch or another of a circuit.
PROTECTION ELEMENTS:
protect circuits and people against potentital problems (electric shocks, fires, etc.)
Types:
Fuses:
melt if the current is too high, interrupting it.
Breaker switches:
are automatic fuses, used in buildings to protect people.
REPRESENTATION AND SYMBOLS
Engineers and electricians don't use pictures when drawing circuits.
So... what do they use to simplify diagrams?
Electric symbols table
EXERCISE 2:
Draw, in your notebook, a circuit using two batteries, two light bulbs, a resistor, a push button and a motor.
EXERCISE 1:
Draw, in your notebook, the following circuit using symbols.
A BRIEF REMINDER...
Voltage (or tension):
is the energy that a battery or generator can provide for each electron. Units: volts (V)
Current:
is the charge, the number of electrons that flow through a conductor per second.
Units: amperes or amps (A).
Resistance:

is the oposition that a component (receiver, conductor, etc.) makes to the flowing of the electric current.
Units: ohms (Ω).
LOOK AT THIS CIRCUITS AND DO THE INDICATED OPERATIONS
???
???
???
How is the voltage in the 3 examples?
How is the current in the 3 examples?
How is the quotient between them?
To this constant equation, we call it the
ohm's law.
It's the most important formula in electronics.

Ohm's law definition:
in a ciruit, the resistance of the component is the quotient of the potential difference (V) across it over the current (I) flowing through it.

R =
V
I
EXERCISE:
Fill in the blank with the correct value, using the ohm's law.
1. SERIES CIRCUITS:
two or more elements are in series when the exit of one is the entrance of the next.
R1
R2
R3
The
current
flowing through all the elements of the circuit is IDENTICAL.
The
voltage
is the SUM of the voltages across each element.
The
total resistance
, or equivalent, of the circuit is:
Re = R1 + R2 + R3
If we connect
several generators
in series...
V = V1 + V2 + V3 +.....
EXERCISE:
Look at the following circuit and calculate...
R1 = 20 Ω
R2 = 15 Ω
R3 = 15 Ω
V = 200V
a) The equivalent resistance.
b) The current flowing through the circuit.
2. PARALLEL CIRCUITS:
the components of the circuit have the same entrance and the same exit.
R3
R1
R2
V
The
voltage
on each element is IDENTICAL.
The
current
on each branch is DIFFERENT.
The
total resistance or equivalent
is:
1
Re
=
+
+
1
1
1
R1
R2
R3
EXERCISE:
Look at the following circuit and calculate...
V = 10V
R1 = 50Ω
R2 = 100Ω
R3 = 100Ω
a) The equivalent resistance.
b) The current flowing through the circuit.
Page 85 exercise 6.2
Page 84 exercise 6.1
EXERCISES TO PRACTISE:
ELECTRIC POWER:
is the capacity of an electric receiver to transform energy in a fixed period of time.
It's measured in
WATTS (W)
We can use the following equation to calculate the power:
P = V x I
VIDEOCONSOLES CONSUMPTION COMPARATIVE
The electric power is directly connected with the
consumption
(electric bill)
1. Electricity and electronics (page 76)
1. Electricity and electronics (page 76)
1. Electricity and electronics (page 76)
1. Electricity and electronics (page 76)
3. Variables of direct current (page 79)
3. Variables of direct current (page 79)
2. Direct and alternating current (page 78)
Direct current (DC):
Is the current (energy) produced when electrons always move in the same direction inside a circuit.
The voltage is constant (always the same).
2. Direct and alternating current (page 78)
Alternating current (AC):
Is the current (energy) produced when the movement of electrons in a circuits vary ciclically.
The voltage is constantly changing (from a positive value to its negative point)
4. Ohm's law (page 80)
4. Ohm's law (page 80)
6. Associations of resistors. Electrical calculations (page 82)
6. Associations of resistors. Electrical calculations (page 83)
5. Electrical energy and power (page 81)
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