Intermediate 1 Physics

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Intermediate 1 Physics . Practical Electricity. Electrical Circuits. Resistance. Mains Electricity. Intermediate 1 Physics . Practical Electricity. Electrical Circuits. Electrical Circuits. A circuit will always have, a source of e _ _ _ _ _ _ _ _ _ energy

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### Intermediate 1 Physics

Practical Electricity

• Electrical Circuits
• Resistance
• Mains Electricity

Beath High School - Int 1 Physics

### Intermediate 1 Physics

Practical Electricity

• Electrical Circuits

Beath High School - Int 1 Physics

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

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Electrical Circuits

complete

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

If the circuit is incomplete, there will be

no c _ _ _ _ _ _ .

current.

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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.

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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

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Circuit Symbols 2

Component

Symbol

Description

converts electrical energy into _ _ _ _ energy

heater

heat

Opposes current; it converts electrical energy into heat

resistor

variable resistor

A resistor whose resistance can be changed

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M

A

V

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

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W

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

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A

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.

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A

Series Circuits

series

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.

one

current

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Parallel Circuits

more

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

parallel

two lamps in p _ _ _ _ _ _ _

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V

Parallel Circuits

lamp, heater and voltmeter connected in parallel.

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V

Parallel Circuits

battery

A parallel circuit.

The b _ _ _ _ _ _ , lamp and

voltmeter are all connected in

p _ _ _ _ _ _ _ .

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

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Measuring Current

ammeter

• Current is measured in amperes (a _ _ _ ).

(The shorthand for amperes is ‘A’)

• Current is measured using an 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

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A

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

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Measuring Voltage
• Voltage is measured in v _ _ _ _ .
• Voltage is measured using a voltmeter

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.

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V

Measuring Voltage

Connecting the voltmeter

Before

After

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.

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A

A

Current and Voltage in Series Circuits

identical

The current through every component in a series circuit

is i _ _ _ _ _ _ _ _ and is the same as the supply

current.

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

series

Each ammeter will have the s _ _ _ reading.

same

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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.

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V

V

V

Current and Voltage in Series Circuits

across

This voltmeter measures the voltage a _ _ _ _ _ the

battery.

This is the supply voltage.

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.

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6V

A

A

0.2A

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

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V

V

V

1V

2V

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

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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.

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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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A

A

A

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.

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Voltage in parallel circuits

identical

The voltage across every component in a parallel circuit

is i _ _ _ _ _ _ _ _ and is the same as the supply

voltage.

The voltage across each lamp can be measured directly.

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V

Voltage in parallel circuits

voltmeter

This v _ _ _ _ _ _ _ _ measures the voltage across the

battery.

This is the supply voltage.

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V

V

V

Voltage in parallel circuits

a r a l l e l

To measure the voltage

across each lamp, connect a

voltmeter in p _ _ _ _ _ _ _

with each lamp.

Each voltmeter will have the

a m e

The supply voltage is the

s _ _ _ as the voltage across

each lamp.

a m e

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### Intermediate 1 Physics

Practical Electricity

• Resistance

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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

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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

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W

Measuring Resistance

h m s

(Shorthand for ohms is “W” – the Greek letter omega)

• Resistance is measured in o _ _ _ .
• 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).

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A

Calculating resistance from ammeter and voltmeter values

Measure the current through the resistor by

connecting an a _ _ _ _ _ _ in s _ _ _ _ _ .

Put the resistor or component into a circuit.

m m e t e r

e r i e s

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A

V

Calculating resistance from ammeter and voltmeter values

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

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voltage

resistance =

current

A

V

Calculating resistance from ammeter and voltmeter values

Calculate resistance using:

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voltage

resistance =

current

A

voltage

12

=

current

0.1

V

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

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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

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### Intermediate 1 Physics

Practical Electricity

• Mains Electricity

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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

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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).

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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

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The three pin plug

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.

1. The live wire (b _ _ _ _ )

o w e r

r o w n

h o c k

i v e

c o n n ec te d

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The three pin plug

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.

2. The neutral wire (b _ _ _ )

a i n s

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The three pin plug

e l l o w

r e e n

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

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

a f e t y

a u l t

a r t h

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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

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cable grip

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

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e a r t h

y e l l o w

b r o w n

u s e

b l u e

cable grip

l i v e

n e u t r a l

Wiring a plug

a n g e r

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!

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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 thel _ _ _ wire of the appliance. This

is so that if something goes wrong, the fusem _ _ _ _

and disconnects the live wire of the appliance from the

m _ _ _ _ power supply.

afety

able

igh

ive

ive

elts

ains

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power

current =

voltage

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:

mpere

mpere

urrent

oltage

ower

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power

current =

voltage

=

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

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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.

ay

ower

eter

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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.

ower

ff

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The Consumer Unit

Mains electricity comes from the power station into your

house through a service cable which goes to the

m _ _ _ _ board.

eter

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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.

ircuits

eparate

arallel

230

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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.).

alls

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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.

use

reaker

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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.

witch

arge

use

ircuit

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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.

ncreases

40

eat

ire

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Some Safety Rules

1. Never use worn or damaged flexes: you could get a

s _ _ _ _ from an exposed live wire.

hock

2. Avoid the use of extensions if possible: too many appliances connected to an extension could produce

o _ _ _ _ _ _ _ _ _ _ at the socket.

verheating

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Some Safety Rules
• Always use the correct flex: a flex which is too
• t _ _ _ could overheat.

hin

4. Always use the correct plug fuse: if the fuse rating is too high and a f _ _ _ _ develops, the flex could overheat.

ault

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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).

urrent

ulb

If there is a current, the series circuit is c _ _ _ _ _ _ _ .

If there is no current, there is a b _ _ _ _ in the circuit.

omplete

reak

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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

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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.

onnected

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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 _ _ _ _ _ _ _ .

esistance

pen

omplete

Safety Point

You must only test a component if there is no chance of there being any

current in it.

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### Intermediate 1 Physics

Practical Electricity

End of Unit

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