Electric Circuits: Day 1
Millikan’s Oil Drop Experiment
• Experiment was done to verify/prove the
charge of an electron (which we now know
is the elementary charge of -1.6 x 10-19 C)
What is an Electric Circuit?
• It is a set of electrical
components including:
1. A source of emf
(electromotive force)
2. A conducting pathway
(conducting wires)
3. A load to consume
energy such as light bulbs,
resistors, or appliances
Sources of Electromotive Force (EMF)
• Electromagnetic – a coil of wire is rotated in a
magnetic field to induce a current (Power
stations use generators to produce a current)
• Chemical – Redox reactions transfer electrons
between chemicals (Batteries are an example)
• Photovoltaic– converts sunlight to electricity
(solar calculators, solar panels)
General Circuit Info
• A current will always take the shortest path in
the circuit (path of least resistance)
• If the current reaches back to the source
without passing through any electrical
components a “short circuit” can occur; the
excess heat could cause a fire without a fuse or
circuit breaker
CURRENT
• Current - the movement of electrons through an
electric circuit
Current Variable
I
Current SI Unit
Amps
• A battery and many appliances utilize direct
current (DC) while your house wiring utilizes
alternating current (AC)
Tesla, Topsy and Edison
A bitter rivalry between electricity-savvy
inventors may sound fictional, but the
tension between Thomas Edison and
Nikola Tesla was real. Tesla championed
alternating current, while Edison insisted
that it was too dangerous. The only
casualties in this "war of currents" were the
animals Edison publicly electrocuted with
Tesla's high voltage system to prove his
point. The early victims were dogs and
cats, but Edison eventually electrocuted an
elephant named Topsy [source: Ruddick].
Voltage (Electric Potential)
• In order for a current to flow, there must be an
electric potential difference between two points;
this is so the electrons have a reason “to do
work” in changing locations
Voltage Variable
V
Voltage SI Unit
Volts
Ex: batteries are named by there electric potential
(voltage) so a 9V battery has the ability to do
more work than a 1.5V battery
Power
• Formula: P = VI
Power
Variable
P
Power SI Unit
Watts
Calculate the power of a motor if the
current through the motor is 3 Amps and
the potential difference is 120 Volts.
P = VI
P = (120)(3)
P = 360 Watts