Download Observations of Electrical Phenomena

Observations of
Electrical Phenomena
ENGR 101
Lecture
Plato’s allegory of the cave …
The prisoners give
names to the
shadows.
Fire is lit behind the prisoners
Puppets perform in front of fire
A gathering of people who have
lived chained to the wall all their
lives
Shadows are cast on the wall
Electric Current
Flow of electric charge
-
-
-
-
- - - - - - - - - - - - - -
Not flow!
Electric Current
Flow of electric charge
-
-
-
-
- - - - - - - - - - - - -
Flow!
Electric Forces
Electric field at point P due to single charge
F
Electric force on a test charge placed at P
Voltage=> Electric Field
Distribution of charge
+++
+++
+++
+++++++++++++++
++
V
--------------------------
+++
+++
+++
Measuring voltage …
Voltage is measured across the
terminals of the resistor, and conveys a
global picture of cause and effect, but
does not convey the information at the
micro level.
1
𝑅=
𝜎𝐴
Measuring current …
The conductivity of a material is a measure of how
easily electrons can travel through the material
under the influence of an externally applied electric
field.
Capacitance
𝜀0 𝐴
𝐶=
𝑑
(Depends on geometry)
Magnetic Forces
Magnetic force
Electromagnetic (Lorentz) force
Magnetic Force on a Current Element
F
F
(B going in to
sheet of paper)
Left-Hand Rule for force
on a wire of current due
to magnetic field
(B going in to
sheet of paper)
Applications
Motor
Railgun