1.
Electric Current Calculations
K Warne
V1
R1
A
VT
V2
R2
A1
A2
2.
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For FULL presentation click HERE >> www.warnescience.net
Electrical Circuits
A
V1
Voltmeter
Ammeter
Resistance
The Ammeter measures
the current flowing in
the circuit. (Amps A)
The Voltmeter Measures
potential difference or
voltage in volts. (V)
The Resistance of the
Resistor is given in
Ohms (Ω).
V1 = V2 V2
3.
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Series Circuits
• Adding resistors in series…increases
the total resistance  because all the
current flows through all the resistors.
Rt = R1 + R2
• The total potential difference (voltage)
is the sum of the potential differences
of the resistors – the total potential
loss must equal the all the potential
lost along the way.
Vt = V1 + V2
The potential differences will be
proportional to the
resistances.
• The current flowing is the same all
over the circuit and would decrease as
more resistances are added 
I = I2 = I3
VTA
V1 V2
R1 R2
VT
V1 v2
A
VT
A2
A3
3Ω1Ω
12v
VT = 12 V
V1 = 3 V
V2 = 9 V
I = ...
4.
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Parallel Circuits
• Adding resistors in
parallel…decreases the total
resistance.
1 1 1
Rt R1 R2
• The potential difference
(voltage) is EQUAL over the
resistances – there is no
potential lost between the
resistors and the cells.
VT = V1 = V2
• The current flowing is divided
between the resistances and
would increase as more
resistances are added more
routes for the current to flow.
= +
V1
R1
A
VT
V2
R2
A1
A2
IT= I1 + I2
5.
Electric Current in a Conductor
Conventional current
 positive to negative
Maintaining a current
Conductor  closed
circuit
Potential difference
Replacement of charges
 SOURCE
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e
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< electrons “Positive spaces” >
Conventional current is the movement of positive “spaces” from + to  in a
conductor.
Conventional current e
If 160 C of charge flow through the ammeter in 3s what current is flowing?
The current is the number
of charges passing any
point in one second
Current (I) = Charge(Q)
Time (t)
6.
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Calculating Current
Calculate the current flowing through the circuit.
+
_
Ammeter
A53.3333
If 160 C of charge flow through the ammeter in 3 s what current
is flowing?
I = Q/t
= 160/3
=53.3 A
7.
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Current & Resistance
RESISTANCE
• Electrical charge experiences resistance as it moves through
a conductor.
• The resistance is due to collisions with particles in the metal
atoms and ions.
• The moving charges lose kinetic energy in the collisions
which heat up the conductor.
+_
CURRENT: An electrical current is a movement of charges
through a conducting material from positive to negative. (?!)
8.
Effects of Current
+_
Electric current generates heat in a conductor.
+_
A small current (0.1A) would have only a few charges flowing.
A large current (15A) would have a large number of charges
flowing and generate far more heat.
As a conductor heats up the RESISTANCE INCREASES.
9.
Factors affecting Resistance
Material: Different materials have different resistance.
Length: Increasing the length will increase the resistance.
Temperature: As temp increases – atoms vibrate faster
RESISTANCE INCREASES.
+ 
+ 
A V
1. Material
2. Length
3. Temperature
R
10.
Current, voltage & resistance
We define the unit of resistance; one ohm () is one volt
per ampere.
R =
V/I 1 = 1V/1A
+ 
+ 
A V
The ratio: Voltage
Current
will always give a constant
value for any resistor.
If the resistance increases
the ratio increases.
We therefore use this ratio
to represent the
resistance of a resistor.
R
Resistance (R) =Voltage (V)
Current (I)
Ohm’s law: The current passing through a resistor is directly
proportional to the potential difference across the resistor provided
the temperature remains constant.
11.
Hi 
This is a SAMPLE presentation only.
My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as
other resources, are freely available on my resource sharing website:
www.warnescience.net
(paste into your browser if link above does not work)
Have a look and enjoy!
Keith Warne
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