beath high school - int 1 physics1 intermediate 1 physics practical electricity electrical circuits...
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Beath High School - Int 1 Physics 1
Intermediate 1 Physics Practical Electricity
Electrical Circuits
Resistance
Mains Electricity
Beath High School - Int 1 Physics 2
Intermediate 1 Physics Practical Electricity
Electrical Circuits
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A circuit will always have,
a source of e _ _ _ _ _ _ _ _ _ energy
an electrical comp _ _ _ _ t
wires forming a c _ _ _ _ _ _ _ path from
one end of the source back to the other end.
electrical
onent
complete
Electrical Circuits
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If the circuit is c _ _ _ _ _ _ _ , there will be
current.
If the circuit is incomplete, there will be
no c _ _ _ _ _ _ .
complete
current.
Electrical Circuits
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Each electrical component has a symbol - called a
"circuit symbol". When we draw circuit
diagrams, we draw the circuit symbol instead of
trying to draw the component itself.
Circuit Symbols
The following table is a list of the circuit symbols
for all the electrical components needed for this
course as well as a brief description of the
function of the component.
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supplies electrical energy
Circuit Symbols 1
Component
Symbol Description
Battery
Open: breaks a circuitClosed: completes a circuit
Converts electrical energy into light energy
lamp
switch
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converts electrical energy into _ _ _ _ energy
Circuit Symbols 2
Component
Symbol Description
heater
A resistor whose resistance can be changed
Opposes current; it converts electrical energy into heatresistor
variable resistor
heat
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Converts electrical energy into kinetic energy
Circuit Symbols 3
Component
Symbol Description
Motor
Used to measure electric current – always connected in series
Used to measure voltage – always connected in parallel
Ammeter
Voltmeter
M
A
V
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Measures resistance directly – use when the component is not connected.
Circuit Symbols 4
Component
Symbol Description
Ohmmeter
A protection device. It melts when the current gets too high.
Fuse
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When components are connected to allow
only one path for the current, we say that
the components are connected in series.
three l _ _ _ _ in serieslamps
lamp, ammeter and fuseconnected in series.
A
Series Circuits
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If the components form a circuit, the circuit
is called a s _ _ _ _ _ circuit.
A series circuit. The battery, switch, lamp, variable resistor and ammeter are all connected in series.There is only o _ _ path for the c _ _ _ _ _ _ from one end of the battery, through each component in turn to the other end of the battery.
series
Aone
current
Series Circuits
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When components are connected to allow m _ _ _
than one path for the current, we say that the
components are connected in parallel.
two lamps in p _ _ _ _ _ _ _
more
parallel
Parallel Circuits
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lamp, heater and voltmeter connected in parallel.
Parallel Circuits
V
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There is more than one separate path
for
the c _ _ _ _ _ _ . You can trace a
separate path from the b _ _ _ _ _ _
through either component back to the
o _ _ _ _ end of the battery.
A parallel circuit.
The b _ _ _ _ _ _ , lamp and
voltmeter are all connected in
p _ _ _ _ _ _ _ .
battery
Parallel Circuits
parallel.
current
battery
other
V
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Current is measured using an a _ _ _ _ _ _
Current is measured in amperes (a _ _ _ ).
(The shorthand for amperes is ‘A’)
To measure the current through a component,
always connect the ammeter in s _ _ _ _ _ with
the component. This means b _ _ _ _ _ _ _ the
circuit to insert the ammeter.
ammeter
Measuring Current
amps
series
breaking
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The reading on the ammeter is the current t _ _ _ _ _ _ the lamp.
Connecting an ammeter
Measuring Current
A
The circuit is altered to include the ammeter in series with the lamp.
AfterBefore
through
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Voltage is measured using a voltmeter
Voltage is measured in v _ _ _ _ .
To measure the voltage across a component,
always connect the voltmeter in p _ _ _ _ _ _ _
with the component.
volts
Measuring Voltage
parallel
(Shorthand for volts is ‘V’)
The voltmeter forms another parallel branch
across the component.
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V
The reading on the voltmeter is the voltage across the l _ _ _ .
Connecting the voltmeter
Measuring Voltage
The voltmeter is added to make another branch in p _ _ _ _ _ _ _ with the lamp.
AfterBefore
parallel
lamp.
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The current through every component in a series circuitis i _ _ _ _ _ _ _ _ and is the same as the supplycurrent.
Current and Voltage in Series Circuits
To measure the current in each lamp, connect an ammeter in s _ _ _ _ _ with each lamp.series
Each ammeter will have the s _ _ _ reading.same
A A
identical
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The sum of the voltages across each component in aseries circuit adds up to the supply voltage.
Current and Voltage in Series Circuits
The voltage across each lamp can be measured directly.
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The voltmeter readings across the lamps a _ _ up to the supply voltage.
This voltmeter measures the voltage a _ _ _ _ _ thebattery.This is the supply voltage.
Current and Voltage in Series Circuits
To measure the voltage across each lamp, connect a voltmeter in parallel with each lamp.
add
across
V V
V
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The current reading on the other ammeter = Aalso the current through each lamp = A
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.
Examples
In a series circuit, the current is the s _ _ _ at all points.
same0.20.2
A A
6V
0.2A
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The supply voltage = 2 + 1= V
2. Find the supply voltage in the circuit shown below.
Examples
In a series circuit, the voltages across each component add up to the supply voltage.
3
V V
V
1V
2V
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The sum of the currents through each component in aparallel circuit adds up to the supply current.
Current in parallel circuits
The current through each lamp and the battery can be measured directly.
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Current in parallel circuits
To measure the current in each lamp, connect an ammeter in s _ _ _ _ _ with each lamp.series
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This ammeter measures the c _ _ _ _ _ _ through thebattery. This is the supply
current.
Current in parallel circuits
To measure the current in each lamp, connect an ammeter in s _ _ _ _ _ with each lamp.
u r r e n t
To measure the current through the battery, connect ana _ _ _ _ _ _ in series with the battery.The ammeter readings a _ _ up to the ammeter reading of the current through the supply.
series
ammeteradd
A
A
A
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The voltage across every component in a parallel circuitis i _ _ _ _ _ _ _ _ and is the same as the supplyvoltage.
Voltage in parallel circuits
The voltage across each lamp can be measured directly.
identical
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This v _ _ _ _ _ _ _ _ measures the voltage across thebattery.This is the supply voltage.
Voltage in parallel circuitsvoltmeter
V
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To measure the voltageacross each lamp, connect avoltmeter in p _ _ _ _ _ _ _ with each lamp.
Voltage in parallel circuits
a r a l l e l
V
Each voltmeter will have the
s _ _ _ reading.The supply voltage is the s _ _ _ as the voltage
acrosseach lamp.
a m e
a m e
V
V
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Intermediate 1 Physics Practical Electricity
Resistance
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An increase in resistance causes a d _ _ _ _ _ _ _
in
current.
The opposition to current is called r _ _ _ _ _ _ _ _ _ .
Materials oppose current and some materials
oppose it
more than others. e s i s t a n c e
Resistance
e c r e a s e
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A resistor causes electrical energy to be converted
into h _ _ _ energy in the material. Sometimes
this is
a nuisance – when circuits heat up and get too h _
_ .
Sometimes it is useful – when heat is required, for
example in k e t _ _ _ _ or cookers.
e a t
Resistance
o t
t l e s
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Resistance can be measured using an o _ _ _ _ _ _
_ .
Resistance is measured in o _ _ _ .h m s
Measuring Resistance
h m m e t e r
(Shorthand for ohms is “” – the Greek letter
omega)To measure resistance, connect the ohmmeter
directlyacross the resistor or component whose resistance
youwant to measure (nothing else connected).
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Measure the current through the resistor byconnecting an a _ _ _ _ _ _ in s _ _ _ _ _ .
Put the resistor or component into a
circuit.
m m e t e r
Calculating resistance from ammeter and voltmeter values
e r i e s
A
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Measure the voltage across the resistor, connecting a
v _ _ _ _ _ _ _ _ in parallel.
Put the resistor or component into a
circuit.
o l t m e t e r
Calculating resistance from ammeter and voltmeter values
V
A
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Calculate resistance using:
Calculating resistance from ammeter and voltmeter values
V
A
resistance =voltage
current
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Calculate resistance using:
Calculating resistance from ammeter and voltmeter values
V
A
resistance =voltage
currentExample:
The current through a resistor is 0.1 amperes when the
voltage across it is 12 volts. Calculate the resistance.
resistance =voltage
current
120.1
= = 120
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When the resistance is reduced,
the current i _ _ _ _ _ _ _ _.
To do this we use a v _ _ _ _ _ _ _ resistor; symbol:
It is often useful to be able to adjust the flow of
current continuously.
a r i a b l e
Variable resistors
n c r e a s e s
For example; controlling the loudness or brightness of
a TV, the heat setting on a toaster, adjusting the
speed of a model train.
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Intermediate 1 Physics Practical Electricity
Mains Electricity
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Mains electricity is dangerous because your body can
c _ _ _ _ _ electricity and mains voltage can cause a
current large enough to k _ _ _ you.Your body conducts even m _ _ _ if it is wet or
damp,
this is the reason why there must be no sockets or
switches in a _ _ _ _ room.
Electricity supplied to houses is called m _ _ _ _
electricity.
Safety Note: Mains electricity is dangerous.
Never experiment with mains electricity. a i n s
MAINS ELECTRICITY
o n d u c t
i l l
o r e
b a t h
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This ensures that each appliance receives the same
voltage (230V).
All mains a _ _ _ _ _ _ _ _ _ in Britain are designed
to operate with a voltage of 230 volts across them.
This means that the household wiring must be such
that all the appliances are connected in p _ _ _ _ _ _ _ .
The declared value of mains voltage is _ _ _ volts2 3 0
MAINS ELECTRICITY
p p l i a n c e s
a r a l l e l
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Household wiring consists of cables in which there
are
t _ _ _ _ wires.
h r e e
The three pin plug
The cable is connected to the m _ _ _ _ using a
three
pin plug – one pin for each of the wires.
a i n s
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The live wire is the wire connected to the 230 volts
supply
from the p _ _ _ _ station. It is coloured
b _ _ _ _ . If you touch the brown wire of an appliance
which is connected to the mains you will get a s _ _ _
_
which can kill you. The switch in an appliance is
always
connected to the l _ _ _ wire so that when the
switch
is off, the appliance is dis _ _ _ _ _ _ _ _ _ from
the 230 V supply from the mains.
1.The live wire (b _ _ _ _ )r o w n
The three pin plug
o w e r
r o w n
h o c k
i v e
c o n n e c t e d
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The neutral wire is used to complete the circuit from
the
appliance to the mains. If you touch the blue wire in
an
appliance you can still get a shock if the appliance is
connected to the m _ _ _ _ and working.
2.The neutral wire (b _ _ _ )l u e
The three pin plug
a i n s
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The earth wire does not normally carry c _ _ _ _ _ _ .
It is a s _ _ _ _ _ device.
It only carries current if there is a f _ _ _ _ in the
appliance. All appliances with metal parts which can
be
touched must have an e _ _ _ _ wire.
3.The earth wire (g _ _ _ _ and y _ _ _ _ _ )r e e n
The three pin pluge l l o w
u r r e n t
a f e t y
a u l t
a r t h
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Appliances are called "double insulated" if it is
impossible
to touch the l _ _ _ wire inside it. These appliances
do
not need an e _ _ _ _ wire and only have a live and
neutral wire. Double insulated appliances have this
symbol
on them.
i v e
Double Insulated appliances
a r t h
Double insulated symbol. Appliances with this symbol do
not have an earth wire since it is impossible to touch any
m _ _ _ _ parts.
e t a l
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_ _ _ _ _ pinEarth wire
(Green/ _ _ _ _ _ _ )
Neutral wire( _ _ _ _ )
Live wire( _ _ _ _ _ )
_ _ _ _ _ _ _ pin
_ _ _ _ pin
F _ _ _
All appliances are connected to the mains power supply by
a three pin p _ _ _ .The plug which connects an appliance to the mains
must beconnected as shown:
l u g
Wiring a plug
e a r t h
y e l l o w
b l u e
n e u t r a l
l i v e
u s e
b r o w n
cable grip
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It is d _ _ _ _ _ ous to operate an appliance if the wires
are not connected as shown here. If you are unsure about
a plug’s wiring, do not use it!
a n g e rWiring a plug
_ _ _ _ _ pinEarth wire
(Green/ _ _ _ _ _ _ )
Neutral wire( _ _ _ _ )
Live wire( _ _ _ _ _ )
_ _ _ _ _ _ _ pin
_ _ _ _ pin
F _ _ _
e a r t h
y e l l o w
b l u e
n e u t r a l
l i v e
u s e
b r o w n
cable grip
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The fuse in a plug is a s _ _ _ _ _ device to protect
the c _ _ _ _ . It melts if the current in the cable
gets too h _ _ _ . All plugs contain a fuse.
The fuse is always connected between the l _ _ _ pin
of the plug and the l _ _ _ wire of the appliance. This
is so that if something goes wrong, the fuse m _ _ _ _
and disconnects the live wire of the appliance from
the
m _ _ _ _ power supply.
a f e t yThe fuse
a b l ei g h
i v ei v e
e l t s
a i n s
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Fuse values are usually 3 a _ _ _ _ _ or 13 a _ _ _ _ _
in
domestic appliances.
It is important to use the correct fuse values to avoid
too
high a c _ _ _ _ _ _. The fuse value can be calculated
from the v _ _ _ _ _ _ and the p _ _ _ _ rating:
m p e r e
Fuse valuesm p e r e
u r r e n to l t a g e o w e r
current =power
voltage
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Example:
Calculate the fuse value required for a mains appliance
with a power of 1150 watts.
13
Fuse values
current =power
voltage
1150230
= = 5A
Therefore a ______ ampere fuse is required.
As a general rule if the power rating is 700 W or more,
a
13 ampere (13 A) fuse must be used. If the power
rating is
less than _____ W a 3 ampere (3 A) fuse must be
used.
700
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Electrical energy is not free! We have to p _ _ for
batteries to get electrical energy from them and we
have
to pay for the electrical energy supplied by the
p _ _ _ _ station. The amount of energy used by a
household is measured by the m _ _ _ _ at the
consumer
unit.
Electrical Powera y
o w e r
e t e r
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Every appliance has a p _ _ _ _ rating marked on it
(usually in kilowatts kW, or watts W).
The greater the power of the appliance, the more/less
energy it uses in one second (this is because it uses
more/less current).
Also, the longer the time the appliance is used, the
more/less energy it uses. So to save energy and
money,
always switch o _ _ appliances after use.
Electrical Power
f f
o w e r
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Scottish Power
kWh
Fusebox for allhousehold
circuits
meter
Main Fuse
Mains electricity comes into a house fromthe power station to the consumer unit.This is where the electricity meter is
Mains electricity comes from the power station into
your
house through a service cable which goes to the
m _ _ _ _ board.
The Consumer Unit
e t e r
Beath High School - Int 1 Physics 55
Scottish Power
kWh
Fusebox for allhousehold
circuits
meter
Main Fuse
Mains electricity comes into a house fromthe power station to the consumer unit.This is where the electricity meter is
From here the mains supply is split into various
domestic
c _ _ _ _ _ _ _ . The lights, power sockets and cooker
each have s _ _ _ _ _ _ _ circuits which are wired in
p _ _ _ _ _ _ _ .
The parallel wiring ensures each circuit has the same
_____ V voltage needed to operate appliances.
The Consumer Unit
i r c u i t se p a r a t e
a r a l l e l
230
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Although the fuse in the three pin plug protects the
cable
of the appliance, it does not protect any wiring in the
house which comes from the mains supply (wires
behind
the w _ _ _ _ , etc.).
Mains Protection
a l l s
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Household wiring is protected at the point where it
comes
into the house - at the consumer unit. Every circuit in
the
house is protected in the mains consumer unit. In
older
houses, a f _ _ _ is used to protect each circuit but in
newer houses and houses which have been recently
rewired, a circuit b _ _ _ _ _ _ is used.
Mains Protection
u s e
r e a k e r
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A circuit breaker is a very fast s _ _ _ _ _ which opens
and disconnects the circuit when the current gets too
l _ _ _ _ . It disconnects the circuit by switching faster
than a f _ _ _ can by melting.
This means that c _ _ _ _ _ _ breakers are much safer
and are gradually replacing fuses altogether.
The circuit Breakerw i t c h
a r g e
u s ei r c u i t
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When appliances are plugged into an extension block,
the
total current i _ _ _ _ _ _ _ _ . A kettle carries a
current of about 10 amperes. If four kettles were to
be
plugged into an extension block, the total current
being
carried would be about ____ amperes.
This very high current causes the cables behind the
wall
or under the floor, to h _ _ _ up and become a f _ _ _
risk. Unfortunately, this is the cause of many house
fires.
Using Extensions
n c r e a s e s
40
e a t i r e
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2. Avoid the use of extensions if possible: too many
appliances connected to an extension could
produce
2. o _ _ _ _ _ _ _ _ _ _ at the socket.
1. Never use worn or damaged flexes: you could get
a
1. s _ _ _ _ from an exposed live wire.
Some Safety Rules
h o c k
v e r h e a t i n g
DANGER
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4. Always use the correct plug fuse: if the fuse rating
is too high and a f _ _ _ _ develops, the flex could
overheat.
3. Always use the correct flex: a flex which is too
t _ _ _ could overheat.
Some Safety Rules
h i n
a u l t
DANGER
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Simple conductors can be tested for continuity by
trying
to pass a c _ _ _ _ _ _ through them in series with
some
indicator device (e.g. a b _ _ _ or ammeter).
Testing for Continuity
u r r e n tu l b
If there is a current, the series circuit is c _ _ _ _ _ _ _ .
If there is no current, there is a b _ _ _ _ in the
circuit.
o m p l e t er e a k
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Switches can be tested, after removing them from
their
circuit, by using this simple continuity tester. There
should be a current with the switch in the O _
position.
There should be n _ current when the switch is
changed
to the OFF position.
Testing for Continuity
N
o
A
indicator(could be a lamp)
resistor to limit current
item to be tested
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This simple continuity tester should not be used for
components which are still c _ _ _ _ _ _ _ _ in their
circuits.
The continuity tester must never be used with
equipment
connected to the mains!
Testing for Continuity
A
indicator(could be a lamp)
resistor to limit current
item to be tested
o n n e c t e d
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When using the multimeter to test for
faults, set the multimeter to measure
r _ _ _ _ _ _ _ _ _ and place the probes
across the component or circuit element.
If the reading is infinity ( a " 1 " shows on the left of
the display) there is an o _ _ _ circuit (this is O.K. if
you
are testing a switch set to OFF). If there is a reading,
the circuit is c _ _ _ _ _ _ _ .
Using a multimeter
e s i s t a n c e
23.04
i tem to be tested
p e n
o m p l e t eSafety PointYou must only test a component if there is no chance of there being anycurrent in it.
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Intermediate 1 Physics Practical Electricity
End of Unit