Download unidad 2: energías no renovables

UNIT 1: ELECTRICITY AND ELECTRONICS
3rd YEAR SUMMARY
TECHNOLOGIES ESO 4
1. WHAT IS ELECTRIC CURRENT?
Electric current is the flow of electrons around a circuit.
Electrons have to “scape” from the nucleus of the atom
to flow, the electrical conductivity depends on the
atomic structure of material.
Pay attention to these atoms:
What are the
differences in the
atomic structure of this
elements ?
2. ELECTRICAL PROPERTIES
CONDUCTORS allow electric currents to pass through
____________
them. All metals belong to this group: copper, iron,
silver…
INSULATORS
___________don’t
allow electric currents to pass
through them. Plastic, wood and glass are examples of
this group.
SEMI-CONDUCTORS have properties which are
_________________
intermediate between previous groups. The most
important examples are silicon and germanium.
3. COMPONENTS OF AN ELECTRICAL CIRCUIT
3.1 GENERATORS
Generators provide the energy for electrons to circulate.
The power for many electrics an electronics circuits
comes from batteries. A battery stores electric energy
and, when connected to a circuit, it provides the force
to the electrons to run along the wires.
Dynamos and alternators are
used for large scale power
generation and industry.
3. COMPONENTS OF AN ELECTRICAL CIRCUIT
3.2 RECEIVERS
They transform electrical energy into another form of
energy. For example, light bulbs, lamps or LEDs
transform electrical energy into light, motors transform
electrical energy into movement, buzzers transform
electrical energy into sound.
3. COMPONENTS OF AN ELECTRICAL CIRCUIT
3.3 CONTROL ELEMENTS
These are elements used to control the flow of
electrons through the circuit. Switches are mechanical
devices that can make (connect), break (disconnect) a
circuit or divert the current from one conductor to
another (circuit switch or crossover switch). A push
button allows the current to flow only when pressure is
mantained.
3. COMPONENTS OF AN ELECTRICAL CIRCUIT
3.4 PROTECTION ELEMENTS
These are elements used to protect the circuit against
excessive current, voltage or current leakage. The most
important elements in this group are fuses (that cuts
the circuit by melting when the current is too high),
breaker switches (automatic fuses) and differential
switches (than protect against current leakage).
4. REPRESENTATION AND SYMBOLS
BATTERIES:
LIGHT BULB/LAMP:
RESISTORS:
MOTOR:
BUZZER/BELL:
LED:
SWITCH:
PUSH BUTTON:
CIRCUIT SWITCH:
INTERESTING WEB:
http://www.clarvis.co.uk/version2/symbols.html
5. ELECTRIC QUANTITIES
5.1 VOLTAGE
Voltage or tension is the energy that a battery or generator can
provide for each electron. Voltage is measured in volts (V).
5.2 ELECTRIC CURRENT
Electric current is the charge, or number of electrons, that flows
through a conductor per second. I = Q/t Electric current is
measured in amperes o amps (A).
5.3 RESISTANCE
Resistance is a measure of how easily (or with what difficulty)
electrons will flow through the device. Copper wire has a very
low resistance, so a small voltage will allow a large current to
flow. Likewise, the plastic insulation has a very high resistance,
and prevents current from flowing from one wire to those
adjacent.
5. ELECTRIC QUANTITIES
5.4 OHM´S LAW
Voltage, current and resistance are quantities related. Current
flowing through a circuit is increased in relation to the voltage
and may also change depending on the material used.
Ohm’s law expresses these relations as follows:
I = V/R
5.5 ELECTRIC POWER AND ENERGY
Electric power is measured in watts (W) and also kilowatt (kW)
Energy in SI units is measured in joules (J), calories (cal) and
kilowatt-hour (kWh)
1 J = 0,24 cal
P = V·I
E = V·I·t = P·t
1 kWh = 3,6 · 106 J
6. SI UNITS
Mega
kilo
Units
milli
micro
nano
Pico
1000,000
1000
1x106
1x103
M
k
Ohms
Ohms
0.001
0.000,001
0.000,000,001
0.000,000,000,001
1x10-3
1x10-6
1x10-9
1x10-12
m
μ
n
p
Amps
Farads
Farads
Farads
p
n
μ
m 1
k
M
-12
-9
-6
-3
+3
+6
0
am x an = am+n
am / an = am-n
7. SOLVING CIRCUITS
7.1 SERIES AND PARALLEL RESISTANCES
Resistors can be wired in parallel or in series, or any combination
there of, so that values greater or smaller than normal or with
higher power or voltage can be obtained. This also allows us to
create new values, not catered for in the standard values.
Some Resistor Combinations
Series: When wired in series, the values simply add
together. A 100 ohm and a 2k2 resistor in series will
have a value of 2k3.
R = R1 + R2 (+ R3, etc.)
Parallel: In parallel, the value is lower than either of the
resistors. A formula is needed to calculate the final value
1/R = 1/R1 + 1/R2 (+ 1/R3 etc)
7. SOLVING CIRCUITS
7.2 MIXED CIRCUITS
Some elements are connected in series and some in parallel:
RT = RP + RS; 1/Rp= 1/10 + 1/7; RP = 4,1k; RT = 5k + 4,1k = 9,1k
IT = VT/RT; IT = 9V/9,1k= 0,98 mA
V5k=IT·R5k = 0,98 mA·5k= 4,9 V ; V7k=V10k = 9V-4,9V = 4,1 V
I7k = V7k/R7k = 4,1V / 7k = 0,58 mA ; I10k= 4,1V/10k = 0,41 mA
(IT = I7k + I10k = 0,58mA+0,41mA=0,99mA)
Rs = 250+1000=1250Ω; 1/RT= 1/Rp= 1/100 + 1/1250; RT = 92,6Ω
IT = VT/RT; IT = 9V/92,6Ω = 0,097A; V100= 9V; I100=V100/R100 =
=9V/100Ω=0,09A; IT=I100+I1250; I1250=0,097A-0,09A=0,007A;
V250=0,007A·250=1,75V; V1k = 9-1,75V = 7,25V
Rs = 10k+10k=20k; 1/RT= 1/Rp= 1/20 + 1/10; RT = 6,7k
IT = VT/RT; IT = 9V/6,7k = 1,34mA; V10k= 9V; I10k=V10k/R10k =
=9V/10k=0,9mA; IT=I10k+I20k; I20k=1,34-0,9=0,44mA;
V10k-10k=0,44mA·10k=4,4V