Electric Current The Flow of Electrons -...
Transcript of Electric Current The Flow of Electrons -...
12/10/2015
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Electric Current
What is Electricity?
• The Flow of Electrons
Closed Circuits
• Circuit – a closed,
continuous conducting
path
• Electric current – the flow
of charges (electrons)
through a wire or any
conductor
What is Voltage?
• It is the electric potential energy per
charge.
• Pushes and pulls electrons through the
circuit.
• Units: volts (v)
Voltage
• Voltage : created by a chemical cell
(battery) or generator
Chemical
Electrical Energy
Mechanical
Electrical Energy
Batteries
• Chemical reactions provide a voltage difference
between the (+) and (-) terminals
• When the terminals are connected, an electrical
current pushes through the conductor because of
the voltage difference
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Chemical Cells
• In Series
– Wired to make a battery
– Increases voltage of battery
• In Parallel
– Do not change voltage
– Makes battery last longer.
Electrical Pressure
• Charge flows from high voltage areas
to low voltage areas
• Voltage difference – the push that
causes charge to move
– Units: volts (v)
Electricity
• Battery: One terminal has extra electrons (-
charge). The other does not (+ charge)
• Pushed by (–) charges and pulled by (+)
charges
What is Electric Current?
• Flow of electrons through a conductor
• The Symbol for CURRENT is I
• Units: Amperes (A)
What is Resistance?
• Resistance – a measure of how much a material opposes the flow of electric current through it
• good conductors – lowresistance
• good insulators – highresistance
Good
Conductor
Good
Insulator
Resistance
– Units: ohms (Ω)
– Affected by four factors:
1. Material it is made of
2. Size of the conductor
– Smaller wires (conductors)
provide more resistance
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3. Length of wire
• Longer wires provide more
resistance
4. Temperature of wire
- the higher the temperature the
greater the resistance
Ohms Law
• One volt pulls one amp through one
ohm of resistance.
• Voltage = current x resistance
• V = I x R
• If R remains the same then what?
• If V remains the same then what?
Calculations using Ohm’s Law
Example #1
What is the voltage difference that flows
through a copper wire if a current of
0.75 amps is flowing through it. The
resistance of the wire is 10 Ω.
V = I * R
Control the Flow
• The flow of electrons is dependent on the voltage difference and the resistance
–The greater the voltage difference, the greater the flow
–The lower the resistance, the greater the flow
• Ohm’s Law
V = I * R
V = voltage (volts)
I = current (amps)
R = resistance (Ohms)