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ELECTRICITY
1. Label the pictures with the name of the device
+
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2. Electric circuit
All electric circuits include:
 An electrical supply, for example a battery.
 An electrical conductor (or conductor), that is, an
electrical path like wires.
 One or more electrical loads like a bulb.
 Control elements like a switch.
3. Units
A battery is a source of electrical energy. It provides the
necessary “pressure” for electricity to flow. This electrical pressure is generally called voltage
and is measured in volts, V.
The flow of electricity is called a current and is measured in amperes or amps, A.
Electrical resistance (or resistance) is the opposition to the flow of current in a circuit. This
value - in ohms, Ω – is a measure of how easily current can flow through the conductors and
components in a circuit.
4. Ohm´s Law
Is a special relation between voltage, current and resistance. The current passing through a lamp
is proportionate to the voltage.
resistance 
voltage
current
or in short R 
V
I
5. Electrical Power
The text below, about electrical power, is from a home improvements magazine.
The amount of current, in amps, required by an electrical appliance — such as a TV or an
electric kettle — depends on the power of the appliance. This number — expressed in watts (W)
— will be marked somewhere on the appliance. To calculate the required current, simply take
the wattage and divide it by the voltage of the electrical supply in your home — around 230 volts
in most of Europe. Therefore, for an electric kettle with a power rating of 2,000 watts (as
specified by the manufacturer), the current required is:
2,000 watts / 230 volts = 8.7 amps
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6. Exercise 1
Complete the exercise below about current and power calculations using the words in the box.
amps conductor
components
current
circuit
resistance
voltage
wattage
ohms supply
volts watts
In electrical calculations, voltage is expressed by the letter V, resistance by the letter R, and
current by the letter I (which comes from the word `intensity').
In other words, the (1) ................................flowing through a (2) .................................measured
in (3) .............................. equals the (4) ................................of the electrical (5)
................................, measured in (6) ................................. divided by the total (7)
.................................measured in (8)............................... To work out the value of R, it is
necessary to calculate the total resistance of all the (9) ................................and connecting
lengths of (10) ................................that make up the circuit.
Once both the voltage and amperage are known, it is possible to work out the power, measured
in (11) ............................ that will be consumed. Power (P) can be calculated using the equation
P = VI. Therefore (12)................................ equals voltage multiplied by amperage.
7. DC and AC
There are two types of current: DC and AC. These acronyms
mean direct current and alternating current.
Batteries are examples of direct current sources; they always
produce a positive charge, and are written with a positive (+).
AC generators produce power from wall sockets, and are
examples of alternating currents; they produce a voltage with
alternating signs that changes from positive (+) to negative
voltage (-).
8. Why do some electrical appliances use DC and some use AC?
The difference between these appliances is basically how they work. DC is useful for appliances
that run on a constant current. All electronic devices use DC. For example, your TV plugs into
an AC wall outlet, but the first thing that the circuitry does is convert the current into DC, which
is what the circuitry requires.
AC is useful for appliances that work a current that is constantly changing. Most motors are
designed to operate by ac.
9. AC generation and use
Electrical mains power is generated (produced) at sites called power stations (or power plants),
which use large generators. A generator converts mechanical energy to electrical energy. A
generator rotates a magnet within an iron case.
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Current from the generators leaves the power station and enters the power grid (or grid) - the
network of power lines (cables) which transmit power around the country. At the point where it
enters the grid, the electricity flows through transformers - specifically step-up transformers,
which increase voltage up to 400,000 volts and decrease amperage or amps. This reduces the
energy lost from the power lines over long distances, as high-voltage (HV) supplies flow more
efficiently than low-voltage (LV) supplies. Before the supply is used by homes and other
buildings, it passes through several step-down transformers, which reduce the voltage and
increase the amperage.
10. DC generation and use
The extraction below is from a consumer magazine.
Photovoltaic cells (PVs) - or solar cells - are an effective way of generating your own electricity
from sunlight. The current they produce can be used immediately, may be stored in
rechargeable batteries (like the ones in cars), or can be fed into the power grid and sold to the
electric company. But PVs produce direct current. This is fine for charging batteries, but is not
suitable for powering household appliances, which require alternating current. For this, the DC
supply from PVs and batteries needs to go through an inverter a device which converts DC to
AC.
11. Exercise 2
Decide whether the sentences below are true or false, and then correct the false sentences.
1 Photovoltaic cells produce direct current.
2 Electrical supply from PVs can be used to charge rechargeable batteries.
3 Rechargeable batteries supply electricity as an alternating current.
4 Inverters convert sunlight to alternating current.
12. Types of Circuit
Series circuits: In this circuit, the current passes through several parts. In the circuit below,
current flows through bulb A, then to bulb B and finally to bulb C. If we add more bulbs, the
lights will be less bright. If any of the bulbs fail or burn out, current cannot flow through the
circuit
and the other components
will not
work.
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Parallel circuits: Current flows through each of the bulbs without having to flow through any
others. If any of the bulbs fail the others will work because current can flow through the rest of
the circuit.
Series / Parallel Circuit: The circuitry below is both a series circuit and a parallel circuit. The
bulbs are in a series circuit but the motors are in a parallel circuit.
Questions:
1. What will happen if one of the motors fails? Will the entire circuit fail?
2. Draw another example of a series and parallel circuit.
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13. Exercises
a. Explain, in English, if the following circuits will work properly and if not correct the
mistakes.
b. Look at the circuit below and mark the bulbs that are lit when the following switches
are pressed:
C, E and F
__________________________________________
B, C, D, E and F
__________________________________________
F
__________________________________________
c. Draw a circuit with:
2 batteries in series
3 bulbs in parallel
1 switch in series with the batteries
d. Draw a circuit with:
2 batteries in parallel
2 bulbs in series
1 switch in series with the bulbs
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e. Complete the following sentences:
1. Electrical systems contain four major components:
1. ____________________
2. ____________________
3. ____________________
4. ____________________
2. The _________ in an electrical system is usually an appliance or machine such as an
electric motor.
3. An electrical __________________ is a material through which charge can easily flow.
4. The ____________________________ can be a switch that turns the current on or off.
5. An _____________________ is a closed path for current to flow created by connecting
voltage sources, conductors, control elements, and loads.
6. There are two types of current: ___________________ and ______________________.
7. In direct current (DC), the electric charge flows in _________ direction.
8. In alternating current (AC), the electric charge flows ____________________________.
9. Batteries produce ____________________ and alternators produce _________________.
10. Batteries can be added together in ___________ to produce a higher voltage.
11. In a series circuit, there is only _______ path for current.
12. In a parallel circuit, there are ______________________ paths for the current to flow.
13. Shorthand symbols:
1. Battery - ____________
2. Light bulb - __________
3. Switch - ____________
4. Conductors - __________
14. Schematic of a simple circuit:
15. An AC voltage source reverses the positive and negative terminals many times per
second. A majority of AC circuits cycle at a rate of ____________. The cycling rate is
called the _________________.
16. Frequency is measured in cycles per second, or ___________.
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f. Create your own wordsearch using the following words or your own ‘relevant’ words.
WIRE
PLIERS
BATTERY
RESISTANCE
BUZZER
BULB
ELECTRICS
COMPONENT
POSITIVE
CABLE
SAFETY
NEGATIVE
SWITCH
CIRCUIT
FUSE
CURRENT
You need two colours for this exercise. Write the above words in one colour and add
extra letters in another.
E
L
E
C
T
R
I
R
C
U
I
T
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I
C
S