Presentation for Senior Level
Students
Learning outcomes:
- An
atom is the basic building block for everything. It is made of protons (positive
charge), electrons (negative charge), and neutrons (no charge)
- The
Bohr model illustrate the arrangement of the subatomic particles (protons and
neutrons are found in the center and the electrons orbit around)
- Insulators are materials that
hold onto electrons tightly while electrons in conductors (metals) easily move
through these materials
- Static
electricity is the charge imbalance that occurs when 2 insulators are rubbed
against each other. Note that charged atoms are called “ions”
- The
triboelectric series ranks materials in order of
their ability to hold or give up electrons (if 2 materials are rubbed against
each other, the one higher on the triboelectric table
will give up electrons and become more positively charged)
- Glass
rod and Silk cloth demo (explained in the Apparatus section under Demo #1)
-
Comb
and Hair demo (explained in the Apparatus section under Demo #2)
-
Coulomb’s
law says that charged objects create an invisible electric field around
themselves. The field is proportional to the charge and varies inversely with
the square of the distance between the charge and point charge
-
The
fundamental principle behind this apparatus is separating opposite charges at
both ends of the rubber belt
-
Materials
(explained in the How to Build a Van
De Graff Generator section)
-
Due
to difference in materials, the belt strips electrons from the upper roller
(made of metal) and transfers it to the bottom
-
When
the electrons reach the lower roller (made of plastic), another charge
separation occurs, giving a negative charge to the roller while the inside
surface of the belt becomes more positive
-
The
lower brush drains away these negative charges to the ground
-
So
what happens to the dome? Due to a series of charge separations between the
upper roller and brush as well as the brush and sphere, there are now excessive
positive charges spread out all over the surface of the dome
-
When
we touch the generator, electrons in our bodies want to attract to the protons
spread out over the dome. This leaves us positively charged. We are now a part
of the generator and the belt is basically stripping electrons from us instead
-
Our
hair is originally neutral, but the tennis balls move away upon contact. Since
there are mostly basketballs left on each strand of hair, the like charges will
repel each other (making our hair stand up)
-
Hair
raising demo (explained in the Apparatus section under Demo #3): If we are connected to the ground,
the VDG grab electrons from us and electrons from the ground in turn flow into
out bodies (this will create a circuit with little charge build up and it is
also bad for the human heart). As a result, a plastic stool is needed to
insulate ourselves from the ground
-
Electric
spark demo (explained in the Apparatus section under Demo #4): This is how
lightning and thunder is created. During a storm, harsh winds rub ice and dirt
together, stripping electrons and causing a massive positive charge build-up.
Since rain creates perfect low resistance air to jump across, electrons get
transferred up from the ground, generating lightning sparks. Note that we see
lightning before hearing thunder because light travels faster than sound
-
Factors
that affect static shocks include material involved, surface area connecting
materials and humidity
-
Since
water conducts electricity (like a superhighway where electrons can easily
travel), humidity allows electrons to “jump” from the ground into our bodies
(which neutralizes the charge imbalance)
-
The
same principle of static electricity applies when we feel a shock upon touching
a metal doorknob on a dry winter day