8.2 – Electric Circuits
Some definitions…
• Current Electricity- continuing motion or flow
of electric charge/electrons in a complete
circuit made by a device such as a battery or
electric generator.
• Electric Circuit = a complete pathway that
allows electrons to flow
• Electric load = any device that transforms
electrical energy into other forms of energy
• Examples of electric loads include light bults,
buzzers, heaters and motors.
Batteries convert chemical energy to
electrical potential energy…
• Chemical energy in the battery give the electrons
on the negative terminal electric potential
energy.
• The electrons are attracted to the positive
terminal of the battery.
• Since there is a pathway for them to travel, the
electrons are pushed by the energy from the
batter through the conducting wire to the load,
where it is turned into a different type of energy
(ex: sound, light, heat etc).
• Electrons travel back to the batter to complete
the circuit.
Electrical Circuit
C: Electrons do not
lose energy in the
wire
D: Electrons lose
potential energy &
do work
A & B:
Electrons get
potential energy in
the battery
E: Electrons don’t
have potential
energy
Think of it this way….
B. Guy has
potential
energy
Stairs =
battery,
(provide
potential
energy)
A. Guy at bottom
of stairs,
(electron)
No potential
energy
C. No change in potential
energy
(electrons passing in wire)
D. Lose potential
energy
(changes to
kinetic energy)
E. Guy has NO
potential
energy
Circuit Components and Diagrams
All circuits are made of four basic
types of parts:
• Source – the source of electrical energy
– Ex: battery, generator, etc.
• Conductor – the wire through which an
electric current can flow
• Load – device that transforms electrical
energy
– Ex: motor, bulb, fan, buzzer, etc.
• Switch – a device that turns a circuit on or off
by closing or opening the circuit.
Circuit Diagrams
• Circuit Diagrams: use symbols to represent
components of the circuit.
Circuit Diagrams
• Circuit Diagrams give an organized
representation of the actual circuit.
• Rules for drawing circuit diagrams:
1. Draw your diagrams with a ruler
2. Make all connecting wires straight lines and 90°
corners.
3. If possible, don’t let conductors cross
4. Your finished diagram should be a rectangle
Example:
Current Electricity and Static Electricity
• The charge in a battery is NOT an example of
static electricity, even though the charge
remains fixed on the battery terminals when
the circuit is not closed.
• Current vs. Static Venn Diagram
Current: The Measure of Flow
• Electric Current: amount of charge passing a
point in a conductor per second.
• Amperes: the measure of electrical current (A)
– Can also be thought of as C/s
• Ammeter: device used to measure current in a
circuit
• The ammeter symbol on a circuit diagram
looks like
Conventional Current
• The conventional current moves from positive
to negative which is opposite of electron flow!
• The concept of electron flow describing
current was not accepted by scientists until
the late 1800’s, after the discovery of the
electron.
Alternating Current and Nikola Tesla…
• http://www.youtube.com/watch?v=iEJNJ0rFSe
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