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2ºESO - Electricity

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Moisés Llorente Santos

on 15 May 2017

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Transcript of 2ºESO - Electricity

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 5: ELECTRICITY.
CIRCUITS

+
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
ELECTRIC VARIABLES
(neutrons and protons form the nucleus)
How does a battery work?
An atom that is not neutral is called an
ion.
DICTIONARY GAME (in 5 groups)
1. MAKE UP A DEFINITION FOR A GIVEN WORD, AND WRITE IT ON A PAPER (5 MINUTES).
2. THE TEACHERS WILL MIX ALL YOUR DEFINITIONS WITH THE CORRECT ONE AND, THEN, WE'LL READ OUT ALL OF THEM.
3. NEXT, EACH GROUP WILL DEBATE FOR 1 MINUTE TO MEET AN AGREEMENT ABOUT THE DEFINITION THEY THINK IS THE CORRECT ONE.
4. YOU'LL GET 1 POINT PER EACH GROUP VOTING YOUR DEFINITION.
5. IF YOUR GROUP GUESSES THE CORRECT ONE, YOU'LL GET 2 POINTS.
6. IF NOBODY GUESS THE CORRECT
DEFINITION, TEACHER WILL GET
1 POINT.
GROUP 1
GROUP 2
GROUP 3
GROUP 4
GROUP 5

MOISÉS
DIRECT
CURRENT
VOLTAGE
RESISTANCE
SWITCH
AMMETER
CAPACITOR
TOTAL
Direct current is a type of current that only flows in one direction
VOLTAGE is the difference of charge between two points.
RESISTANCE is the opposition of a material to the flow of an electric current.
A
switch
is an element that directs the current lowing through a branch of a circuit.
An
ammeter
is a device used to measure currents.
An
capacitor
is an electronic component that can store charge.
Moisés Llorente
Colegio Madrigal (Fuenlabrada)
Technologies 3º ESO

How many electric quantities do you know?
Voltage (or tension):
Is the energy that a battery or generator can provide for each electron. It is measured in volts (V).
How many electric quantities do you know?
Electric Current:
Is the charge, or number of electrons, that flows through conductor per second. It is measured in amperes (A).
How many electric quantities do you know?
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 (PAGE 131)
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. Controls the electric flow.
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 interrupts it.
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).
THE OHM'S LAW
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.
TYPES OF CIRCUIT
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.
TYPES OF CIRCUIT
1. 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 134 exercise 11
Page 148 exercise 6
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)
Which particles is matter made of?
Matter is made of atoms.
What is electricity?
Electricity is the energy produced when electrons jump from one atom to another.
When these electrons flow through a cable (conductor) an electric current is produced.
So... what do we need to produce electricity?
A lot of free electrons
Something to provide
them some energy
And... how can we take advantage of the energy produced by the flow of the electrons?
+
N
N
+
-
-
-
-
-
Lots of negative
charges
Lots of positive
charges
-
+
+
N
+
+
N
N
+
N
+
Inestability
Stability
-
-
-
-
-
-
-
-
-
-
-
-
I
V
R
Full transcript