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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 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 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 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
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
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
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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