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 - the movement of electrons through an electric circuit

• A battery and many appliances utilize direct current (DC) while your house wiring utilizes alternating current (AC)

CURRENT

Current Variable Current SI Unit

I Amps

Tesla, Topsy and EdisonA 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].

• 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

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

Voltage (Electric Potential)

Voltage Variable Voltage SI Unit

V Volts

Power• Formula: P = VI

Calculate the power of a motor if the current through the motor is 3 Amps and

the potential difference is 120 Volts.

P = VIP = (120)(3)

P = 360 Watts

Power Variable

Power SI Unit

P Watts