Topic 7 - ElectricityElectricity

• Charges• Electrons• Voltage• Current• Series• Parallel• Resistance

The slides are designed to tie in with a set of worksheets, but could be adapted or serve as a template for other teachers

Topic 7 page 1

4. I charged up a plastic comb by

When I put the charged-up comb near some foil

rubbing it rubbing it with a duster/pulling it through with a duster/pulling it through my hairmy hair the foil jumped up to stick the foil jumped up to stick to the combto the comb

Topic 7 page 2

ItemItem What it was What it was rubbed onrubbed on

Did the bits Did the bits of foil move?of foil move?

Plastic comb hair

Plastic ruler hair

Plastic bag cloth

Wooden ruler cloth

Plastic pen cloth

Metal spatula cloth

Text

yesyesyes

noyes

no

Topic 7 page 3

The electroscope

Stop!

Topic 7 page 4

Object ChargedObject Charged Effect on Gold LeafEffect on Gold Leaf

Plastic comb

Plastic rod

Plastic bag

Plastic ruler

Rises upRises upRises upRises up

If an uncharged object is brought near an electroscope the gold leafIf a charged object is brought near an electroscope the gold leaf

doesn’t move.rises up.

Topic 7 page 6

Pulling and Pushing

Pull together

Charged object Charged object 11

Charged object Charged object 22

What What happened?happened?

Comb Cling film

Cling film Cling film

Cling film Piece of record

Polythene rod Polythene rod

Polythene rod Perspex rod

Perspex rod Perspex rod

Pull together

Pull togetherPush apart

Push apart

Push apart

Topic 7 page 6

Is there a pattern?

Pull together

Charged object Charged object 11

Charged object Charged object 22

What What happened?happened?

Comb Cling film

Cling film Cling film

Cling film Piece of record

Polythene rod Polythene rod

Polythene rod Perspex rod

Perspex rod Perspex rod

Pull together

Pull togetherPush apart

Push apart

Push apart

samesame PushPush apart

samesame PushPush apart

samesame PushPush apart

differentdifferent PullPull together

differentdifferent PullPull together

differentdifferent PullPull together

Topic 7 page 6

5. If the charged objects are the same material then they will repel

Topic 7 page 7

Where Does Charge Come From?

The centre of the atom contains both yellow neutrons and green positive protons

Around the outside are the negative electrons

1. There are kinds of electrical charge called

2.a) To make an object positively charged you need to b) To make an object negatively charged you need to

3. If a substance is neutral it means that

Topic 7 page 7

twtwoopositive and negativepositive and negative

remove negative remove negative chargeschargesadd negative add negative chargescharges

the negative charges are exactly the negative charges are exactly balanced by the positive balanced by the positive chargescharges

Topic 7 page 8

4. Two charged polythene rods will repel because

5. A cleaned mirror will be dusty within 24hrs because

6. A woolen jersey could be attracted to a nylon shirt because

they have the same they have the same chargecharge

the charge attracts dustthe charge attracts dust

they would have they would have opposite charges which would opposite charges which would attractattract

Topic 7 page 10

1. A Van de Graff generator

2. a) Your hair stands on end when you touch a Van de Graff generator because

b) Your hair goes down when you touch a

water tap because

builds up builds up and stores a negative chargeand stores a negative charge

your hairs become your hairs become negatively charged and repel negatively charged and repel each othereach other

the negative the negative charges leave you flowing charges leave you flowing along the pipes to the ground along the pipes to the ground and the hairs stop repelling and the hairs stop repelling

Topic 7 page 11

Now fill the Now fill the blanksblanks

When a flows, charges are currentcurrent movinmovingg

-----------

Topic 7 page 12

BatteryBattery

AmmeteAmmeterr

A

Bulb Bulb

Switch Switch

Topic 7 page 13

Part of circuit StatementBattery measures current

Bulb pushes the current

Switch changes electrical energy to light

Ammeter carries current round circuit

Connecting wire turns the current on and off

The a bulb the bigger the

Topic 7 page 14

Dim bulb Bright bulb– small current - large current

brightbrighterer

currencurrentt

Topic 7 page 14

1. a) An electric circuit

b) A complete circuit has

5. A B C D

is a path that is a path that electricity can flow alongelectricity can flow along no gaps allowing no gaps allowing electricity to flow along itelectricity to flow along it

0.2A0.2A 0.5A0.5A 0.65A0.65A 0.95A0.95A

Topic 7 page 15

A

A

A.

A

Topic 7 page 15

B.

A

Topic 7 page 15

C. V

V

2a)The battery b) The wires c) The ammeter d) The switch3a) The energy change in the bulb is

b) The energy change in the battery is

4a) Electricians use symbols to

Topic 7 page 17

pushes the current through the wires

conduct the electricitymeasures the current

opens and closes a gap

Electrical energy Light energyChemical energy Electrical energy

make their diagrams clearer and tidier

0.2

Topic 7 page 18

X

A

AY

Z

Current at X A

Current at Y A

Current at Z A0.20.2

A0.2

A

A

0.2

0.2

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

same same

0.2

Topic 7 page 19

X

Y

Z

Current at X A

Current at Y A

Current at Z A0.20.4

A

A

A

0.2

0.2

0.4

In a parallel circuit the current taken from the battery the sum of the currents through the two bulbs

equals equals

Topic 7 page 20

Q1. The two bulbs in circuit B make less light than the one bulb in circuit A because

Q2. No current flows in circuit C because

Q3.

Q4. House lights are better wired in parallel than series; a) b)

B shares the current between two (dim) bulbs one of the bulbs is blown creating a break in the circuit

don’t dim

Broken bulb doesn’t put whole house into darkness

Using Voltmeters and AmmetersUsing Voltmeters and Ammeters

Voltmeter – connected in parallel

V

A

Ammeter connected in seriesseries

Correctly Wired?

V

No! The voltmeter has been connected in series – it should be parallel

Correctly Wired?

A

No the Ammeter has been connected in parallel – it should have been series

Correctly Wired?

A

Yes! This Ammeter has been connected correctly in series

Correctly Wired?

A

Yes! This Ammeter has been connected correctly in series

Correctly Wired?

VYes! The Voltmeter has been connected correctly in parallel

Correctly Wired?

A Yes! The Ammeter has been connected correctly in series

Effects of Series?

As more bulbs are added in series the bulbs grow dimmer

Topic 7 page 23

Circuit Diagram

Conductors

Insulators

IronBrassCopperSteelGraphite

PlasticRubberPerspexGlassWood

Topic 7 page 25

Wire Observation Use

Nichrome

copper

Tin-lead

Glows red hot

Conducts doesn’t get

hot Heats up

and melts

Electric fire

Conducting wires

Safety fuse

Topic 7 page 26, 27

Battery Battery voltage

Bulb brightness

1.

2.

3.

1.5 V

6 V

12 V

dim

brighterbright

When the voltage increases the current increases

Topic 7 page 28

5. Write down your ideas.

• The more batteries the brighter the bulb• This holds true as long as the batteries face the same way• If batteries are reversed they cancel each other out

Elephant handout

Topic 7 page 29

Text

Animation 1

Title:

Aim:

Method:

Topic 7 page 30

Choosing the best type of cable

To compare copper/nichrome, thick/thin, long/short wires and find the best Test thick and thin wires in a circuit and measure how it affects the current using an ammeter. Then test copper/nichrome and long/short wires.

Topic 7 page 30

Diagram:

Results:

A bulb may be used instead of an ammeterAWire Current

long

short

copper

nichrome

thick

thin

Topic 7 page 30

Conclusion:

• Short wires are better than long wires.• Copper wires are better than nichrome wires.• Thick wires are better than thin wires.

Topic 7 page 31

Copper has a resistance than nichrome

Thin wires have resistance than thick ones

Longer wires have resistance than short ones

lower

higher

higher

Topic 7 page 32

The variable resistor

4. Write down what you found out.

The longer the wire (coil) the dimmer the bulb, the shorter the wire the brighter the bulb.

Topic 7 page 33

The variable resistor

Write down what you found out.

The longer the wire (coil) the smaller the current and the dimmer the bulb.The longer wire has a higher resistance.

1. A long thin nichrome wire has a higher resistance because

2. a) Thick copper wires are good for carrying current because

b) Long thin coils of nichrome are used in electric fires because

Topic 7 page 35

thick has a lower resistance, as does copper and short wires.

copper is a good conductor and thick wires have low resistance

nichrome has a high resistance causing it to heat up without melting

Topic 7 page 35

3. A variable resistor is used to

4. When the volume on a radio is turned

Down

5. Cookers need thick cabling

increase and decrease the current by changing the length of a resistance wire

the resistance wire is the resistance wire is lengthened, causing a lengthened, causing a reduction in the current.reduction in the current.

because because they use much more current than they use much more current than lampslamps

Topic 7 page 36

The purpose of a fuse is to protect you from a short circuit - safetysafety

NotNot to make the device work

Circuit Symbols

(components used in slides)

VA

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