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Current Electricity
What Happened Here??
https://www.youtube.com/watch?v=0OK0VKz9mkc
https://www.youtube.com/watch?v=TIy3GqS-cd8
Electric Current –
The rate that
electric charges
move through a
conductor.
Unit is Ampere.
1 Amp = 1 Coulomb
1 Second
Forget
the
Coulomb,
I just
need a
regular
COMB!
Electrical Resistance
The tendency of a
material to resist the
flow of electrons*.
* Caused by collisions (and
friction) of charges and atoms
of the conductor.
A light bulb is a resistor. It
changes electrical energy into
light and thermal energy
Electrical Resistor – Device
designed to slow the movement
of electrical current.
Ohm’s Law
The ratio of voltage
across a conductor
to the current it
carries.
Resistance (R) = Voltage (V)
Current (I)
Measured in Ohms.
1 Ohm (Ω) = 1 Volt
1 Ampere
Georg Ohm
(1787 – 1854)
No e for me just
G-E-O-R-G!
V
I
R
1. If the current through a certain
resistor is 6.2 Amps and the
voltage across the resistor is
110V, what is the resistance?
2. If the Voltage across a
flashlight bulb is 3V and the
bulbs resistance is 6Ω, what is
the current through the bulb?
Electrical Circuit
An assembly of
electrical devices
connected so that
it provides a
predictable,
controlled path
for the electrical
current.
Series Circuit –
A circuit that
forms a single
path for electrical
current.
Parallel Circuit
A circuit consisting of devices
connected at common points that
provide two or more paths for electrical
current.
Schematic Diagram
A diagram that
uses standard
symbols to
represent
components of an
electrical circuit.
Schematic Diagram
What type of circuit?
In a Series Circuit;
• The current is the equal throughout
the circuit.
• The equivalent resistance is the
sum of the individual resistors.
REq = R1 + R2 + R3
• The total voltage is the sum of the
voltage drops across each resistor.
For the following circuit determine;
• The current
• The equivalent resistance.
• The voltage drop across each
resistor.
In a Parallel Circuit;
• The total current is the sum of the
currents through each path.
• The equivalent resistance is the
sum of the individual resistances.
1
=
1
1
1
REq
R1 + R2 + R3
• The voltage is the same for each
resistor.
For the following circuit determine;
• The total current
• The equivalent resistance.
• The voltage drop across each
resistor.
In a Series-Parallel Circuit;
1. Draw a schematic.
2. Calculate the equivalent resistance for
parallel resistors.
3. Re-draw schematic.
4. Calculate the new equivalent
resistance for series resistors.
5. Find the total current.
6. Go backwards to find voltage drops
and currents across individual
resistors.
Circuits
- Combine equivalent resistance
for resistors R3 + R4.
R34 = R3 + R4 = 5 Ω + 15 Ω = 20 Ω
- Re-draw schematic.
Calculate the new equivalent
resistance for parallel resistors.
-
1 = 1 + 1 = 15Ω
REq 60Ω 20Ω
- Re-draw
schematic.
- Calculate the new equivalent
resistance for series resistors.
Req = 25 Ω + 15 Ω + 20 Ω = 60Ω
- Find total current and voltage
drops across individual resistors.
I = 120V = 2 Amps
60Ω
- Finally, calculate the current
through each parallel resistor
(using the voltage for each section)
I = 30V = 0.5 Amps
60Ω
I = 30V = 1.5 Amps
20Ω
etc…