Activity 1 – “Wireless” communication - Meldrum Academy

safflowerpepperoniMobile - Wireless

Nov 24, 2013 (3 years and 7 months ago)

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L Hogg @ Glenwood 2005

1

PRACTICAL ELECTRICITY


ELECTRICAL CIRCUITS


We build circuits from
components
. When we draw circuits we always use
circuit symbols drawn with a ruler.


Circuit Symbols




























Component



Circuit symbol


Description


Battery






Supplies ____________








energy.


Lamp







Converts electrical to








__________ energy.


Switch






Open: _________ a circuit.








Closed: ________ a circuit.


Heater






Converts electrical energy








into ___________ energy.


Resistor






Opposes current. Converts








electrical energy into ________.


Variab
le resistor





A resistor whose ___________








can be changed.


Motor







Converts electrical energy








into ___________ energy.


Ammeter






Used to measure ___________.








Always connected in ________.


Voltmeter






Used to measure ___
________.








Always connected in ________.


Ohmmeter






Used to measure ___________.


Fuse







A ____________ device.








It ___________ when the








____________ is too high.


L Hogg @ Glenwood 2005

2


In order for current to flow around a circuit
it must be
complete
. If
there are any gaps no current can flow. There are 2 types of circuit we
can build.


Series circuits


When components are connected in series there is only ___________
path for the current to take to pass through them.


Lamp, a
mmeter and fuse
connected in series.

















A series circuit. There is only one


A






path for the ____________ to








take to get from one end of the








battery, through each _________








to the other end of the ba
ttery.


Parallel circuits


When the components are connected in parallel there is __________
_________ one path for the current to take to pass through them.










Lamp, heater and voltmeter








Connected in parallel.




V











A parallel circuit. There is more

than one path for the _________
to take to get from one end of the
_________ to the other.

L Hogg @ Glenwood 2005

3


Measuring current


Current

is the
flow of electricity or charge

around a circuit.

Current is measured using an __
____________.

Current is measured in _________ , usually given the symbol A.

To measure current through a component, the ammeter is always
connected in __________ with the component. This means breaking the
circuit to connect the ammeter.











Measuring voltage


Voltage

is the push provided by the
battery or power supply
.

Voltage is measured using a _________________.

Voltage is measured in ___________, usually given the symbol V.

To measure voltage across a component, the voltmeter is al
ways
connected in _______________ with the component.

This can be done without breaking the circuit. The voltmeter forms a
parallel branch across the component.









Without Ammeter

Redraw the circuit showing an
ammeter in the correct position.

Without Voltmeter

Redraw the circuit showing a
vol
tmeter in the correct position

L Hogg @ Glenwood 2005

4


Current and Voltage in Series Circuits.




The current through every compo
nent in a series circuit is equal.







A







A








This means the readings on these ammeters would be _____ ______.






The voltages across each component in a series circuit add up to
the supply voltage
.



Vs






V
1









V
2





This means that the voltage across the lamps V
1

and V
2

_________ to
the supply voltage Vs.



L Hogg @ Glenwood 2005

5


Examples


1.

In the circuit shown, the current reading on one of the ammeters is
0.2 amperes. Find the current

reading on the other ammeter and
the current through each lamp.







6V





A







A 0.2A







In a series circuit the current is the same at all points.



Current reading on the other ammeter = _______ A



Current t
hrough each lamp = _______ A



2.

Find the supply voltage in the circuit below.



Vs






2V









2V





In a series circuit, the voltage across each component adds up to
the supply voltage.



Supply voltage = _____ + _____ = _____ V


L Hogg @ Glenwood 2005

6


Current and Voltage in Parallel Circuits.




The currents through each branch add up to the current from the
supply.










As












A
1












A
2


This means that the readi
ng on ammeters 1 and 2 would _________


up to the reading on ammeter As.





The voltage across every branch is identical and is equal to the
supply voltage.








Vs











V
1











V
2




This means that th
e reading on voltmeter Vs is __________ to the
reading on V
1
, which is __________ to the reading on V
2
.

L Hogg @ Glenwood 2005

7


Examples


1.

In the circuit shown, the readings on ammeters 1 and 2 are 0.5A.
What is the reading on ammeter As from the supply.











As










0.5A











A
1











0.5A










A
2


In a parallel circuit, the current in each branch adds up to the
current from the supply.



Current through ammeter As = _____ + _____ = _____A.


2.

In the circuit below V
1

a
nd V
2

both read 6V. What is the voltage
across the supply?








Vs










V
1











V
2



In a parallel circuit the voltage across each branch is identical and
is equal to the supply voltage.




Vs = V
1

= V
2

= _______ V.

L Hogg @ Glenwood 2005

8

RESISTANCE


Materials try to stop current from flowing through them. We say they
oppose

current. Some materials oppose current more than others.

The opposition to current is called
resistance
.


An increase in resistance causes current to ___
______________.


A resistor causes electrical energy to be changed to _________ energy
in the material. Sometimes this is a nuisance


when circuits heat up and
get too hot. Sometimes it can be useful


when heat is required, for
example in __________ or _
_________.



Measuring resistance


Resistance i
s

measured in __________ , usually given the symbol

.


Resistance can be measured using an _______________.



In the box below draw the circuit you would use to measure the
resistance of a resistor directly u
sing an ohmmeter.















L Hogg @ Glenwood 2005

9


Measuring resistance from ammeter and voltmeter values









The circuit shown can be used to







calculate the resistance of the resistor.


A












The current through the resistor and







the vo
ltage across it are measured.






V




The following equation can then be used






to calculate resistance







Example


The current through a resistor is 0.1A when the voltage across it is 12V.

Calculate the resistance.


Resistance =
voltag
e

=



=






current



Variable resistors


It is often useful to be able to adjust the flow of current in a circuit.

For example; controlling the loudness or brightness of a TV, the heat
setting on a toaster, adjusti
ng the speed of a model train. To do this we
use a variable resistor.


When the resistance is reduced, the current _______________.




Resistance =
voltage





current

L Hogg @ Glenwood 2005

10

MAINS ELECTRICITY



Mains electricity is dangerous. Never experiment with electricity.


Electricity supplied to houses is c
alled mains electricity. Mains electricity
is dangerous because your body can conduct electricity and mains voltage
can cause a current large enough to kill you. Your body conducts
electricity even better when it is wet or damp. This is why there are no
so
ckets in a bathroom.


The declared value of mains voltage is __________ V.



The three pin plug


All appliances are connected to the mains supply by a three pin plug.


In the box below draw a three pin plug, label each wire either live,
neutral or earth an
d colour each one the correct colour.


















L Hogg @ Glenwood 2005

11




The live wire

The live wire is connected to the 230V supply from the power station.
It is coloured ____________. If you touch the live wire of an
appliance you will get a shock which could kill you. T
he switch in an
appliance is always connected to the live wire so that when the switch
is off, the appliance is disconnected from the mains supply.




The neutral wire

The neutral wire is used to complete the circuit from the appliance to
the mains. It is co
loured ______________. If you touch the neutral
wire you can still get a shock.




The earth wire

The earth wire does not normally carry ______________. It is a
____________ device, which protects the ___________ It only
carries a current if there is a _____
_______ in the appliance. All
appliances with ____________ parts that can be touched must have
an earth wire. The Earth wire is coloured ________ and ________.



Double insulated appliances


Some appliances are double insulated. This means that it is impos
sible to
touch the live wire inside. If an appliance is double insulated it does not
need an __________ wire and there are only ____ wires in the flex; the
__________ wire and the __________ wire.


In this space draw the double

insulated symbol which would


be found on the rating plate of

a double insulated appliance.



Appliances that have the double insulation symbol usually have

______________ casings.

L Hogg @ Glenwood 2005

12


The fuse


The fuse is a _____________ device which protects the ___________.


In the space below expl
ain how the fuse works.


______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
_______________
_______________________________________
______________________________________________________
______________________________________________________
______________________________________________________



Fuse Values



Fuse values are usually _____ ampere o
r _____ ampere in domestic
appliances.


It is important to choose the correct fuse value to avoid too high a
current flowing through the appliance. The fuse value is calculated by
first calculating the current which flows through the appliance when it is
w
orking properly.





Current = _____________



The next value of fuse up is then used.





L Hogg @ Glenwood 2005

13


Example


Calculate the fuse value required for a mains appliance with a power of
1150 watts.




Current =
power

=

1150

= 5A





voltage

230


So a 13 ampere fuse should be used.












Mains voltage is always ___________ V.

Household wiring connects appliances in ______________ so they all
receive the ___________ voltage.



Example:


What size of fuse should be used in a 460W applia
nce?









As a genera
l rule:

If the power rating is 700W or more, a 13 ampere (13A) fuse
should be used.

If the power rating is less than 700W, a 3 ampere (3A) fuse
should be used.

L Hogg @ Glenwood 2005

14


The consumer unit


Mains electricity comes from the

power station into your house

through a service cable which

goes to the meter board.


From here the mains supply is

split into various domestic

circuits. The lights, power

sockets and cooke
r each have

separate circuits which are wired

in parallel. The parallel wiring ensures each circuit has the same 230V
needed to operate the appliance.



Mains protection


Although the three pin plug protects the flex of the appliance, it does
not protect a
ny wiring behind the walls. Household wiring is protected
where it enters the house


at the consumer unit.


In older houses this is done with fuse wire. In newer houses a circuit
breaker is usually used.


In the space below explain how a circuit breaker w
orks and give the
advantages of a circuit breaker compared with a fuse.


______________________________________________________
______________________________________________________
______________________________________________________
_____________________
_________________________________
______________________________________________________

______________________________________________________

______________________________________________________

L Hogg @ Glenwood 2005

15


Safety rules


In the space below list 4 safety rules yo
u should

remember when dealing with electricity. For each,

give a reason why this rule is important. The first one

has been started for you







DANGER



1.

Rule ______________________________________________


____________________________________________
______

__________________________________________________

Reason ____________________________________________

__________________________________________________
__________________________________________________


2.

Rule ____________________________________
__________

__________________________________________________

__________________________________________________

Reason ____________________________________________

__________________________________________________
_________________________________________
_________


3.

Rule ______________________________________________

__________________________________________________

__________________________________________________

Reason ____________________________________________

____________________________________
______________

__________________________________________________


4.

Rule ______________________________________________

__________________________________________________

__________________________________________________

Reason _______________________
_____________________

__________________________________________________
__________________________________________________

L Hogg @ Glenwood 2005

16


Testing for continuity


Simple conductors can be tested for continuity by trying to pass a
current through them in series with some
indicator device. (e.g. a bulb or
an ammeter).




If there is a very high current, the circuit is _________________.



If there is no current, the circuit is ________________________.


In the box below draw the circuit diagram for a circuit which could be
used

to test for continuity.
















Switches can be tested by removing them fr
om

their circuit and
connecting them in the above circuit.

There should be a current when the switch is in the ______ position and
no current when the switch is in the ____
_ position.


Continuity testers must never be used for any components still
connected into circuits or for any equipment connected to the mains.



L Hogg @ Glenwood 2005

17


Using a multimeter


When using a multimeter to test for faults,


set the multimeter to measure

___________
and place the probes

across the component to be tested.


If the reading is _________________

(a “1“ shows on the left of the display),

there is an _________ circuit.


If there is a zero reading, the circuit is

________________.


If there is no fault i
n the circuit, the ohmmeter will read somewhere in
between these two values.


Electrical power


Electrical energy is not free. We have to pay for the energy supplied by
the power station. The energy used by a household is measured by the
meter at the consu
mer unit.


Every appliance has a power rating marked on it (usually in watts W or
Kilowatts kW). The greater the power, the more energy used per second.


Also the longer the time an appliance is switched on for, the more energy
it uses. So to save energy a
nd money,
always switch off appliances after
use.


Energy used by an appliance depends on

1.

_________________________________________________

2.

_________________________________________________