Download Series circuits - Eyemouth High School

S3 Physics – Exam revision
Electric current (I) is the flow of electric
charge around a circuit and is measured in
amperes (A)
Voltage is a measure of the energy given to the
charges in the circuit. Voltage is measured in
volts (V)
Electrical symbols
• Cell
• A.C. Supply
?Low Voltage Supply?
• D.C. Supply
• Resistor
• Lamp
• Voltmeter
• Ammeter
• Switch
?connecting wire?
Page 9 Physics study mate will help
Circuit symbols
These symbols are used so that everyone worldwide can
understand a circuit diagram when they see it.
Series circuits
• In a television series, you get several episodes, one after
the other. A series circuit is similar. You get several
components one after the other.
• If you follow the circuit diagram from one side of the cell
to the other, you should pass through all the different
components, one after the other, without any branches.
• In a series circuit, if a lamp breaks or a component is
disconnected, the circuit is broken and all the components
stop working.
New
Cell symbol
What will be the Ammeter readings on A 1 - 3
We measure electric current ( flow of electrons)
with an ammeter (A). The circuit symbol for an
ammeter is :
A
An ammeter must always be connected in series
8V d.c.
A1
3
2
1
A2
A3
A4
What is actually going on in
electric circuits?
• http://www.bbc.co.uk/learningzone/clips/anintroduction-to-electricity/10596.html
• Cell v battery
v
---
From the diagram above, what is the reading at:
1) Position 1: more than 0.1 A, 0.1 A or less than 0.1 A
2) Position 2: more than 0.1 A, 0.1 A or less than 0.1 A
3) Position 3: more than 0.1 A, 0.1 A or less than 0.1 A
Voltage
Voltage is a measure of the energy given to the
charges in the circuit. We measure voltage in
volts (V). The circuit symbol for a voltmeter is :
V
A voltmeter must always be connected in parallel
8V d.c.
v1
1
v3
v2
2
3
• Resistance is measured in ohms – if a
substance has a high resistance it will not
allow electricity to flow through it
http://www.youtube.com/watch?v=BBa42qpKyfg
Ohms law calculations
Calculate the resistance of the
resistor in the circuit. The current is
5A, the voltage across the resistor is
15V.
A
15V
5amp
Step 1: Choose the correct equation
V
I
Step 2: Write down the equation.
R=V÷I
Step 3: Fill in the numbers for V and I.
R = 15 ÷ 5
Step 4: work out your answer and do not
forget to put in the correct units.
R =3 Ω
R
Copy and complete this table :-
Voltage
Current
Resistance
0.2 A
60
12V
1000
230V
48
230V
100 mA
1.5V
20 mA
V
I
R
Copy and complete this table :-
Voltage
Current
Resistance (Ω)
12 V
0.2 A
60
12V
0.012 A
1000
230V
4.8 A
48
230V
100 mA
2300
1.5V
20 mA
75
V
I
R
Hair Dryer Super model
1.
230 V
2.
50 Hz
600 Watts
3.
Which electrical quantity is
measure in watts?
Calculate the current in the
hair dryer
What size fuse should be
fitted?
P = IV
I =P
V
I = 600
230
= 2.6 Amp
• Page 19 Success Guide Q 1 -5
Appliance
Likely power rating
Clock
Upto 720 Watts
Hair dryer
500 Watts
Heater / fire
3,000 Watts
Vacuum cleaner
1400 Watts
Television
100 Watts (not a flat screen giant TV)
Cooker
12000
The fuse
13 amp or 3 amp
• A safety device found in plugs & main
fuse box
• If a larger current than normal flows
then the fuse will melt
• This cuts off the electricity
• The flex of my hair dryer only has two
wires which terminal does not have a
wire attached to it?
Type of wire
Colour of wire
Live
Brown
Earth
Green and
yellow
Blue
Neutral
The element of a heater has a current of
1.25 amps and is plugged into UK mains
voltage, what is it’s resistance?
-
A
+
Granny has a 1800 watt electric heater, she uses it 8
hours per day for one week – how many kilowatt-hours are
used by Granny?
Series and parallel circuits
1. What happens to the current flowing around these circuits?
2. How would you describe the voltage in each of these
circuits?
3. How do we calculate the total resistance of each of these
circuits?
Resistors in Parallel
15 Ω
30 Ω
10 Ω
10 Ω
10 Ω
5Ω
From what we have learnt so far in Physics –
Copy & Accurately complete this table
Series
Current
Voltage
Total
Resistance
Parallel
How did you do ?
Out of ten?
Series
Parallel
Current
Is the same at all
points
The sum of currents in
parallel branches is
equal to the current
drawn from the supply
Voltage
The sum of voltages
across components in
series is equal to the
supply voltage
The voltage across
components in parallel
is the same for each
component
Total
Resistance
R
1 = 1+ 1
Rtotal R1 R2
total
= R 1 + R2
http://www.bbc.co.uk/bitesize/standard/physics/using_electricity/movement_from
_electricity/revision/3/
•
On the following diagram of a basic DC electric
motor label: the axle, the brushes, the
commutator, the armature, the magnets, the
current carrying loops.
http://www.bbc.co.uk/bitesize/standard/physics/using_electricity/move
ment_from_electricity/revision/3/
Electric motor
• Commercial motors are different in several ways from the
simple model discussed here.
• A commercial motor has carbon brushes for good electrical
contact with the commutator and also so that when the brushes
wear away, they can easily be replaced. Carbon brushes do not
wear away as quickly as metal brushes
• A commercial motor has a multi-section commutator - two
sections for each of several rotating coils wound in different
planes. Although only one of these coils carries a current at any
one time, having a lot of them makes the rotation far more
smooth.
• A commercial motor uses field coils not a permanent magnet.
These coils become magnetised when a current is passed
through them. Field coils give a stronger, more easily shaped
magnetic field than permanent magnets. cheaper / lighter
Step 1: Choose the correct equation
V
I
Step 2: Write down the equation.
R=V÷I
Step 3: Fill in the numbers for V and I.
R = 15 ÷ 5
Step 4: work out your answer and do not
forget to put in the correct units.
R =3 Ω
R
We used an oscilloscope to view the difference
between direct and alternating current
Alternating current (a.c.) is
when the current changes
direction every fraction
of a second. 50 times
every second in UK.
Direct current (d.c.) is
when the current passes
in one direction only.
Batteries supply d.c.