PSC 151
Laboratory Activity 8
Electric Circuits I
An Introduction
Electricity
The Ancient Greek philosopher Thales of Miletus around 600 BC,
reported that charge (or electricity) could be accumulated by
rubbing fur on various substances, such as amber. The Greeks
noted that the charged amber buttons could attract light objects
such as hair. They also noted that if they rubbed the amber for long
enough, they could even get a spark to jump.
In 1600 the English scientist William Gilbert coined the modern
Latin word electricus from the Greek word for "amber", which
soon gave rise to the English words electric and electricity
All electrical phenomena derive from two of the particles that
compose every atom: electrons, protons.
nucleus
neutrons
electrons
protons
The electron and the proton have an intrinsic property called
electric charge.
Properties of Electrons, Protons, and Neutrons
Electron:
Charge = -1.6x10-19 Coulombs
Mass = 9.11x10-31 kg
Proton:
Charge = +1.6x10-19 Coulombs
Mass = 1.672x10-27 kg
Neutron:
Charge = 0
Mass = 1.674x10-27 kg
Electric Current: Moving Electric Charge
Conventional current was defined early in the history of electrical
science as a flow of positive charge.
In solid metals, like wires, the positive charges are immobile, and
only the negatively charged electrons flow in the direction opposite
conventional current,
An electric circuit is a closed path around which electric charge
flows.
An electric circuit consists of a source of the moving electric
charge such as a battery and other devices such as a light bulb or
motor.
The source of moving electric charge provides electrical energy to
the circuit while devices like lights and motors convert the electrical
energy into other forms…light, heat, mechanical energy.
In an electric circuit there must be a complete path through which
the charge can move from the source, through any external devices
and return to the source.
For an external device such as a light bulb to work the current
must flow through that device.
Glass
Housing
Filament
Filament
Supports
Threaded
Side of
Base
Tip of
Base
Base
Heavy Duty
+
In drawing electric circuits symbols are often used to represent
different circuit components.
wire
battery
+ + -
light bulb