Transcript Electricity practical

Topic 7 - Electricity
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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 rubbing it
with a duster/pulling it through my hair
When I put the charged-up comb near
some foil the foil jumped up to stick to
the comb
Item
Topic 7 page 2
What it was
rubbed on
Plastic comb
hair
Plastic ruler
hair
Plastic bag
cloth
Wooden ruler
cloth
Plastic pen
cloth
Metal spatula
cloth
Did the bits of
foil move?
yes
yes
yes
no
yes
no
Topic 7 page 3
The electroscope
Stop!
Topic 7 page 4
Object Charged
Plastic comb
Plastic rod
Plastic bag
Plastic ruler
Effect on Gold Leaf
Rises
Rises
Rises
Rises
up
up
up
up
If an uncharged object is brought near an
electroscope the gold leaf doesn’t move.
If a charged object is brought near an
electroscope the gold leaf rises up.
Topic 7 page 6
Pulling and Pushing
Charged object 1
Charged object 2
Comb
Cling film
Cling film
Cling film
Polythene rod
Polythene rod
Perspex rod
What happened?
Pull together
Cling film
Push apart
Piece of record Pull together
Polythene rod
Push apart
Perspex rod
Pull together
Perspex rod
Push apart
Topic 7 page 6
Is there a pattern?
Charged object 1
Charged object 2
What happened?
Cling film
different
Cling film
Cling film
same
Cling film
Piece of record
different
Polythene rodsame
Polythene rod
Polythene roddifferent
Perspex rod
Perspex rod same
Perspex rod
Pull together
Push apart
Pull together
Push apart
Pull together
Push apart
Comb
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?
Around the
outside are the
negative electrons
The centre of the
atom contains
both yellow
neutrons and
green positive
protons
Topic 7 page 7
1. There are two kinds of electrical charge
called positive and negative
2.a) To make an object positively charged
you need to remove negative charges
b) To make an object negatively charged
you need to add negative charges
3. If a substance is neutral it means that
the negative charges are exactly
balanced by the positive charges
Topic 7 page 8
4. Two charged polythene rods will repel
because they have the same charge
5. A cleaned mirror will be dusty within
24hrs because the charge attracts dust
6. A woolen jersey could be attracted to a
nylon shirt because they would have
opposite charges which would attract
Topic 7 page 10
1. A Van de Graff generator builds up and
stores a negative charge
2. a) Your hair stands on end when you
touch a Van de Graff generator
because your hairs become
negatively charged and repel each
other
b) Your hair goes down when you touch a
water tap because the negative
charges leave you flowing along the
pipes to the ground and the hairs
stop repelling
Topic 7 page 11
When a current flows, charges are moving
-
Now fill the
blanks
Topic 7 page 12
Battery
A
Switch
Bulb
Ammeter
Topic 7 page 13
Part of circuit
Battery
Statement
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
Topic 7 page 14
Dim bulb
– small current
Bright bulb
- large current
The brighter a bulb the bigger the current
Topic 7 page 14
1. a) An electric circuit is a path that
electricity can flow along
b) A complete circuit has no gaps allowing
electricity to flow along it
5. A 0.2A
B 0.5A
C 0.65A D 0.95A
Topic 7 page 15
A.
A
A
Topic 7 page 15
B.
A
A
Topic 7 page 15
C.
V
V
Topic 7 page 17
2a)The battery pushes the current through
the wires
b) The wires conduct the electricity
c) The ammeter measures the current
d) The switch opens and closes a gap
3a) The energy change in the bulb is
Electrical energy  Light energy
b) The energy change in the battery is
Chemical energy  Electrical energy
4a) Electricians use symbols to make their
diagrams clearer and tidier
Topic 7 page 18
Z
A
X
0.2
Y
A
0.2
A
0.2
Current at X
Current at Y
Current at Z
0.2 A
0.2 A
0.2 A
In a series circuit the current is the same at all
points in the circuit.
Topic 7 page 19
A
0.4
Z
A
0.2
A
0.2
Current at X
Current at Y
Current at Z
0.2 A
0.2 A
0.4 A
X
Y
In a parallel circuit the
current taken from the
battery equals the sum of
the currents through the
two bulbs
Topic 7 page 20
Q1. The two bulbs in circuit B make less light
than the one bulb in circuit A because B shares
the current between two (dim) bulbs
Q2. No current flows in circuit C because one of
the bulbs is blown creating a break in
the circuit
Q3.
Q4. House lights are better wired in parallel
than series; a) don’t dim
b) Broken
bulb doesn’t put whole house into
darkness
Using Voltmeters and Ammeters
Voltmeter –
connected in
parallel
V
A
Ammeter
connected in
series
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?
V
Yes! 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
Iron
Brass
Copper
Steel
Graphite
Plastic
Rubber
Perspex
Glass
Wood
Topic 7 page 25
Wire
Observation
Nichrome
Glows red
hot
copper
Tin-lead
Use
Electric
fire
Conducts
Conducting
doesn’t get
wires
hot
Safety
Heats up and
fuse
melts
Topic 7 page 26, 27
Battery
Battery
voltage
Bulb
brightness
1.
1.5 V
dim
2.
6 V
brighter
3.
12 V
bright
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
Topic 7 page 30
Title: Choosing the best type of cable
Aim:To compare copper/nichrome,
thick/thin, long/short wires and find the
best
Method: 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:
Wire
long
short
copper
nichrome
thick
thin
Current
A bulb may be
used instead of
an ammeter
A
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 lower resistance than
nichrome
Thin wires have higher resistance than
thick ones
Longer wires have higher resistance than
short ones
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.
Topic 7 page 35
1. A long thin nichrome wire has a higher
resistance because thick has a lower
resistance, as does copper and
short wires.
2. a) Thick copper wires are good for
carrying current because copper is a
good conductor and thick wires have
low resistance
b) Long thin coils of nichrome are used in
electric fires because nichrome has
a high resistance causing it to heat
up without melting
Topic 7 page 35
3. A variable resistor is used to
increase and decrease the current
by changing the length of a
resistance wire
4. When the volume on a radio is turned
Down the resistance wire is
lengthened, causing a reduction
in the current.
5. Cookers need thick cabling because they
use much more current than lamps
Topic 7 page 36
The purpose of a fuse is to protect you
from a short circuit - safety
Not to make the device work
Circuit Symbols
(components used in slides)
A
V
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