Beath High School - Int 1 Physics1 Intermediate 1 Physics Practical Electricity Electrical Circuits Resistance Mains Electricity

Beath High School - Int 1 Physics 1

Intermediate 1 Physics Practical Electricity

Electrical Circuits

Resistance

Mains Electricity



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

Electrical Circuits


If the circuit is c _ _ _ _ _ _ _ , there will be

current.

If the circuit is incomplete, there will be

no c _ _ _ _ _ _ .

complete

current.

Electrical Circuits


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.


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


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


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


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


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


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


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


lamp, heater and voltmeter connected in parallel.

Parallel Circuits

V


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


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


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


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.


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.


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


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


The voltage across each lamp can be measured directly.


The voltmeter readings across the lamps a _ _ up to the supply voltage.

This voltmeter measures the voltage a _ _ _ _ _ thebattery.This is the supply voltage.


To measure the voltage across each lamp, connect a voltmeter in parallel with each lamp.

add

across

V V

V


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


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


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.



To measure the current in each lamp, connect an ammeter in s _ _ _ _ _ with each lamp.series


This ammeter measures the c _ _ _ _ _ _ through thebattery. This is the supply

current.


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


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


This v _ _ _ _ _ _ _ _ measures the voltage across thebattery.This is the supply voltage.

Voltage in parallel circuitsvoltmeter

V


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



Resistance


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


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


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).


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


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


V

A


Calculate resistance using:


V

A

resistance =voltage

current


Calculate resistance using:


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


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.



Mains Electricity


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


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


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


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


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


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


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


_ _ _ _ _ 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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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

A

indicator(could be a lamp)

resistor to limit current

item to be tested


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!


A

indicator(could be a lamp)

resistor to limit current

item to be tested

o n n e c t e d


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.



End of Unit

Documents

Beath High School - Int 1 Physics1 Intermediate 1 Physics Practical Electricity Electrical Circuits Resistance Mains Electricity