Presentation for Senior Level Students

Learning outcomes:

1. Atom:

-     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)

1. Like charges repel / Opposite charges attract:

-     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

1. Van de Graff Generator:

-          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

1. Conclusion:

-          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