Transcript Electrical &Potential Differences

Amps, Volts and
Resistance (Ohm’s Law)
Coulomb
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Recall that one Coulomb has 6.25 X 1018
electrons.
If the current coming out of the outlet on
the wall has 600 C, how many electrons are
coming out of the outlet?
1C = 6.25 X 1018 electrons
600 C
e-
Cross multiply and you get 3.75 X 1021 electrons
Current Intensity
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Symbol: I
Units:Amperes, A
Current Intensity - the amount of
electrons that flow past a given point in a
circuit every second (i.e through a wire)
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A
Example:
0.7 amperes is shown by
I = 0.7 A
An ammeter is the instrument used to
measure current intensity
Current Intensity
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The current intensity in a circuit can be
determined using the formula:
I = q/t
I is the current intensity in amps (A)
q is the charge in coulombs (C)
t is time in seconds (s)
NOTE: 1 Amp (A) = 1 Coulombs (C)/1 second (s)
A=C/s
Example:
What is the current flowing through a
car headlight if there are 900 C of
charge used in 1 minute?
I = q/t
I = 900 /60
I = 15A
Example:
How much charge does it take to
operate an MP3 player for 15
minutes if the current is 2A?
I = q/t
2 = q/900
q = 1800C
Potential Difference
(Voltage)
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Symbol: V
Units:Volts, V
Potential Difference is the amount of
energy transferred between two points in
an electrical circuit.
Example: Energy that is provided by a
battery or power supply. It could be a 12
volts battery (also know as 12V)
V
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A voltmeter is used to measure potential
difference
Potential Difference (Voltage)
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The potential difference in a circuit can be
determined using the formula:
V=E/q
V is potential difference in volts (V)
E is the energy in joules (J)
q is the electric charge in coulombs (C)
Note: 1 Volts = 1 Joule / 1 Coulombs
V=J/C
Example

In a house, how much energy is
provided by 120V service providing
200C of charge?
V=E/q
120 = E/200
E = 24 000J
Resistance
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Symbol: R
Units:Ohms, Ω
Resistance is how difficult it is for
current to flow
Resistance is the opposite of conductance!
A resistor is used to slow current down
and convert electrical energy into
heat energy (e.g. light bulb, stove
Resistor–
Conductor –
element).
high resistance &
low conductance
low resistance &
high conductance
Ohm’s Law

Ohm’s Law states – that for a
given resistance, the potential
difference in an electrical circuit is
directly proportional to the current
intensity.
Formula to Solve Circuits
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Resistance, current intensity and potential
difference are all related
R = V/I
R is the resistance in Ohm’s (Ω)
V is the potential difference (Volts)
I is the current intensity (Ampere)
Note: 1 Ohms= 1 Volts / 1 Ampere
1 (Ω) = 1 V / 1 A
Example
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An stove element 30 Amperes going
through it, and carries 120 volts of
electricity, how much resistance is
in this circuit?
R = V/I
R = 120 V/30 A
R = 4 V/A = 4 Ω
Example
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A circuit has a potential energy
difference of 240 V and offers a
resistance of 6Ω, what is the
intensity of the current flow?
R=V/I
6 = 240 /I
I = 240 /6
I = 40 A
Example
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A circuit has a resistance of 10Ω & a
current intensity of 5A. What is the
potential difference?
R=V/I
10 = V/ 5
10 X 5 = 50V
Summary Table
Resistance
Current
Potential
Difference
Definition
Slows current
down
The flow of
electrons
Causes
electrons to
flow
Symbol
R
I
V
Units
Ohms (Ω)
Amps (A)
Volts (V)
I=q/t
A=C/s
V=E/q
V=J/C
Ammeter or
formula
Voltmeter or
formula
Formula
(if applicable)
How measured
(if applicable)
R=V/I
Ω=V/I
Circuit
Formula