Intermediate 1 Physics

1
Intermediate 1 Physics

• Practical Electricity

• Electrical Circuits

• Resistance

• Mains Electricity

2
Intermediate 1 Physics

• Practical Electricity

• Electrical Circuits

3
Electrical Circuits

• 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
4
Electrical Circuits

• If the circuit is c _ _ _ _ _ _ _ , there will
  be current.
• If the circuit is incomplete, there will be
• no c _ _ _ _ _ _ .

complete
current.
5
Circuit Symbols

• 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.

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.
6
Circuit Symbols 1
Component
Symbol
Description
supplies electrical energy
Battery
Converts electrical energy into light energy
lamp
Open breaks a circuit Closed completes a circuit
switch
7
Circuit Symbols 2
Component
Symbol
Description
converts electrical energy into _ _ _ _ energy
heater
heat
Opposes current it converts electrical energy
into heat
resistor
A resistor whose resistance can be changed
variable resistor
8
Circuit Symbols 3
Component
Symbol
Description
Converts electrical energy into kinetic energy
Motor
Used to measure electric current always
connected in series
Ammeter
Used to measure voltage always connected in
parallel
Voltmeter
9
Circuit Symbols 4
Component
Symbol
Description
Measures resistance directly use when the
component is not connected.
Ohmmeter
A protection device. It melts when the current
gets too high.
Fuse
10
Series Circuits

• When components are connected to allow only one
  path for the current, we say that the components
  are connected in series.

three l _ _ _ _ in series
lamps
lamp, ammeter and fuse connected in series.
11
Series Circuits

• If the components form a circuit, the circuit is
  called a s _ _ _ _ _ circuit.

series
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.
one
current
12
Parallel Circuits

• When components are connected to allow m _ _ _
  than one path for the current, we say that the
  components are connected in parallel.

more
parallel
two lamps in p _ _ _ _ _ _ _
13
Parallel Circuits
lamp, heater and voltmeter connected in parallel.
14
Parallel Circuits

• A parallel circuit.
• The b _ _ _ _ _ _ , lamp and
• voltmeter are all connected in
• p _ _ _ _ _ _ _ .

battery
parallel.
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.
current
battery
other
15
Measuring Current

• Current is measured using an a _ _ _ _ _ _

ammeter

• Current is measured in amperes (a _ _ _ ).
• (The shorthand for amperes is A)

amps

• 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.

series
breaking
16
Measuring Current

• Connecting an ammeter

After
Before
The circuit is altered to include the ammeter in
series with the lamp.
The reading on the ammeter is the current t _ _
_ _ _ _ the lamp.
through
17
Measuring Voltage

• Voltage is measured using a voltmeter

• Voltage is measured in v _ _ _ _ .

volts
(Shorthand for volts is V)

• To measure the voltage across a component, always
  connect the voltmeter in p _ _ _ _ _ _ _ with
  the component.

parallel
The voltmeter forms another parallel branch
across the component.
18
Measuring Voltage

• Connecting the voltmeter

After
Before
The voltmeter is added to make another branch in
p _ _ _ _ _ _ _ with the lamp.
parallel
The reading on the voltmeter is the voltage
across the l _ _ _ .
lamp.
19
Current and Voltage in Series Circuits

• The current through every component in a series
  circuit
• is i _ _ _ _ _ _ _ _ and is the same as the
  supply
• current.

identical
To measure the current in each lamp, connect an
ammeter in s _ _ _ _ _ with each lamp.
series
Each ammeter will have the s _ _ _ reading.
same
20
Current and Voltage in Series Circuits

• The sum of the voltages across each component in
  a
• series circuit adds up to the supply voltage.

The voltage across each lamp can be measured
directly.
21
Current and Voltage in Series Circuits

• This voltmeter measures the voltage a _ _ _ _ _
  the
• battery.
• This is the supply voltage.

across
To measure the voltage across each lamp, connect
a voltmeter in parallel with each lamp.
The voltmeter readings across the lamps a _ _
up to the supply voltage.
add
22
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.

In a series circuit, the current is the s _ _ _
at all points.
same
The current reading on the other ammeter
A also the current through each lamp
A
0.2
0.2
23
Examples

• 2. Find the supply voltage in the circuit shown
  below.

In a series circuit, the voltages across each
component add up to the supply voltage.
The supply voltage 2 1 V
3
24
Current in parallel circuits

• The sum of the currents through each component in
  a
• parallel circuit adds up to the supply current.

The current through each lamp and the battery can
be measured directly.
25
Current in parallel circuits
To measure the current in each lamp, connect an
ammeter in s _ _ _ _ _ with each lamp.
series
26
Current in parallel circuits
u r r e n t

• This ammeter measures the c _ _ _ _ _ _ through
  the
• battery. This
  is the supply current.

To measure the current in each lamp, connect an
ammeter in s _ _ _ _ _ with each lamp.
series
To measure the current through the battery,
connect an a _ _ _ _ _ _ in series with the
battery.
ammeter
The ammeter readings a _ _ up to the ammeter
reading of the current through the supply.
add
27
Voltage in parallel circuits

• The voltage across every component in a parallel
  circuit
• is i _ _ _ _ _ _ _ _ and is the same as the
  supply
• voltage.

identical
The voltage across each lamp can be measured
directly.
28
Voltage in parallel circuits
voltmeter

• This v _ _ _ _ _ _ _ _ measures the voltage
  across the
• battery.
• This is the supply voltage.

29
Voltage in parallel circuits

• To measure the voltage
• across each lamp, connect a
• voltmeter in p _ _ _ _ _ _ _
• with each lamp.

a r a l l e l
Each voltmeter will have the s _ _ _ reading.
a m e
The supply voltage is the s _ _ _ as the
voltage across each lamp.
a m e
30
Intermediate 1 Physics

• Practical Electricity

• Resistance

31
Resistance

• Materials oppose current and some materials
  oppose it
• more than others.

The opposition to current is called r _ _ _ _ _
_ _ _ _ .
e s i s t a n c e
An increase in resistance causes a d _ _ _ _ _ _
_ in current.
e c r e a s e
32
Resistance

• 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
o t
t l e s
33
Measuring Resistance

• Resistance is measured in o _ _ _ .

h m s
(Shorthand for ohms is W the Greek letter
omega)

• Resistance can be measured using an o _ _ _ _ _
  _ _ .

h m m e t e r
To measure resistance, connect the ohmmeter
directly across the resistor or component whose
resistance you want to measure (nothing else
connected).
34
Calculating resistance from ammeter and voltmeter
values

• Put the resistor or component into a circuit.

Measure the current through the resistor
by connecting an a _ _ _ _ _ _ in s _ _ _ _ _ .
m m e t e r
e r i e s
35
Calculating resistance from ammeter and voltmeter
values

• Put the resistor or component into a circuit.

Measure the voltage across the resistor,
connecting a v _ _ _ _ _ _ _ _ in parallel.
o l t m e t e r
36
Calculating resistance from ammeter and voltmeter
values

• Calculate resistance using

37
Calculating resistance from ammeter and voltmeter
values

• Calculate resistance using

Example The current through a resistor is 0.1
amperes when the voltage across it is 12 volts.
Calculate the resistance.
resistance
120W
38
Variable resistors

• It is often useful to be able to adjust the flow
  of
• current continuously.

For example controlling the loudness or
brightness of a TV, the heat setting on a
toaster, adjusting the speed of a model train.
To do this we use a v _ _ _ _ _ _ _ resistor
symbol
a r i a b l e
When the resistance is reduced, the current i _
_ _ _ _ _ _ _.
n c r e a s e s
39
Intermediate 1 Physics

• Practical Electricity

• Mains Electricity

40
MAINS ELECTRICITY

• Safety Note Mains electricity is dangerous.
• Never experiment with mains electricity.

Electricity supplied to houses is called m _ _ _
_ electricity.
a i n s
Mains electricity is dangerous because your body
can c _ _ _ _ _ electricity and mains voltage
can cause a current large enough to k _ _ _ you.
o n d u c t
i l l
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.
o r e
b a t h
41
MAINS ELECTRICITY
The declared value of mains voltage is _ _ _
volts
2 3 0
All mains a _ _ _ _ _ _ _ _ _ in Britain are
designed to operate with a voltage of 230 volts
across them.
p p l i a n c e s
This means that the household wiring must be
such that all the appliances are connected in p
_ _ _ _ _ _ _ .
a r a l l e l
This ensures that each appliance receives the
same voltage (230V).
42
The three pin plug

• Household wiring consists of cables in which
  there are
• t _ _ _ _ wires.

h r e e
The cable is connected to the m _ _ _ _ using a
three pin plug one pin for each of the wires.
a i n s
43
The three pin plug

• 1. The live wire (b _ _ _ _ )

r o w n
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.
o w e r
r o w n
h o c k
i v e
c o n n e c t e d
44
The three pin plug

• 2. The neutral wire (b _ _ _ )

l u e
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.
a i n s
45
The three pin plug

• 3. The earth wire (g _ _ _ _ and y _ _ _ _ _ )

r e e n
e l l o w
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.
u r r e n t
a f e t y
a u l t
a r t h
46
Double Insulated appliances
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
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
47
Wiring a plug
All appliances are connected to the mains power
supply by a three pin p _ _ _ . The plug which
connects an appliance to the mains must
be connected as shown
l u g
e a r t h
y e l l o w
b r o w n
u s e
b l u e
l i v e
n e u t r a l
48
Wiring a plug
It is d _ _ _ _ _ ous to operate an appliance
if the wires are not connected as shown here. If
you are unsure about a plugs wiring, do not use
it!
a n g e r
49
The fuse
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 y
a b l e
i g h
i v e
i v e
e l t s
a i n s
50
Fuse values
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
m p e r e
u r r e n t
o l t a g e
o w e r
51
Fuse values
Example Calculate the fuse value required for a
mains appliance with a power of 1150 watts.
1150
5A
230
Therefore a ______ ampere fuse is required.
13
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
52
Electrical Power
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.
a y
o w e r
e t e r
53
Electrical Power
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.
o w e r
f f
54
The Consumer Unit
Mains electricity comes from the power station
into your house through a service cable which
goes to the m _ _ _ _ board.
e t e r
55
The Consumer Unit
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.
i r c u i t s
e p a r a t e
a r a l l e l
230
56
Mains Protection
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.).
a l l s
57
Mains Protection
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.
u s e
r e a k e r
58
The circuit Breaker
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.
w i t c h
a r g e
u s e
i r c u i t
59
Using Extensions
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.
n c r e a s e s
40
e a t
i r e
60
Some Safety Rules

• 1. Never use worn or damaged flexes you could
  get a
• s _ _ _ _ from an exposed live wire.

h o c k

• 2. Avoid the use of extensions if possible too
  many appliances connected to an extension could
  produce
• o _ _ _ _ _ _ _ _ _ _ at the socket.

v e r h e a t i n g
61
Some Safety Rules

• Always use the correct flex a flex which is too
• t _ _ _ could overheat.

h i n
4. Always use the correct plug fuse if the fuse
rating is too high and a f _ _ _ _ develops, the
flex could overheat.
a u l t
62
Testing for Continuity
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).
u r r e n t
u 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 e
r e a k
63
Testing for Continuity
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.
N
o
64
Testing for Continuity
The continuity tester must never be used with
equipment connected to the mains!
This simple continuity tester should not be used
for components which are still c _ _ _ _ _ _ _ _
in their circuits.
o n n e c t e d
65
Using a multimeter
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 _ _ _ _ _ _ _ .
e s i s t a n c e
p e n
o m p l e t e
Safety Point You must only test a component if
there is no chance of there being any current in
it.
66
Intermediate 1 Physics

• Practical Electricity

End of Unit