17.1 Electric Chargepp.

Mr. Richter

Agenda

Warm-Up

Introduction to Electricity and Magnetism

Explore Van de Graaff Generator

Notes: Electric Charge Transfer of Electric Charge

Conductors and Insulators Methods of Charging

Objectives: We Will Be Able To…

Understand the basic properties of electric charge.

Differentiate between conductors and insulators.

Distinguish between charging by contact, charging by induction, and charging by polarization.

Warm-Up:

When you feel an electric shock, what do you think is happening? Why does this occur?

Electric Charge

Electricity at an Atomic Level

All matter has electric charge because it contains:

protons (positive charge), and

electrons (negative charge)

Most moving charge comes from electrons because they: are smaller and lighter on the outside of

atoms

Electric Charge

Like magnets like charges repel each other and unlike charges attract.

Electric Charge

Electric charge is conserved. If an object gives electrons to

another object, it becomes more positively charged while

the other object becomes negatively charged.

Losing electrons = more positive

Gaining electrons = more negative In the picture above, the balloon gains electrons from the woman’s hair.

Quantifying Electric Charge

Because charge comes from the transfer of electrons, all amounts of charge are multiples of the charge of an electron (e).

Charge (q) is measured in Coulombs [C]. electron: -1.60 x 10-19 C proton: 1.60 x 10-19 C neutron: 0 C

A charge of -1.0 C (1/e) contains 6.2 x 1018 electrons. Therefore, 1 Coulomb is a HUGE amount of charge. A lightning bolt has a charge of about 25 C.

The Transfer of Charge

Conductors and Insulators

Conductors allow electrons to flow freely through them. Charge is easily distributed through

the material evenly. Most metals.

Insulators inhibit the flow of electrons. Excess charge has nowhere to go,

and remains on the surface. Glass, rubber, silk, plastic…

Charging by Contact

When two materials are rubbed together, like balloons and hair, electrons are physically knocked off the hair onto the balloon.

This is charging by contact.

Conductors that are charged quickly become neutral unless protected by an insulator. Think copper rod with a rubber

handle. Or screwdrivers.

Charging by Induction

If an object is grounded, it can be charged by induction. No electrons transfer between the objects.

Excess electrons flee to the ground when a charged object is brought nearby, leaving a positive charge.

This is induction. The charge is induced on the object.

Polarization

A surface charge can be induced in insulators.

The electrons can’t flow, but they can turn away. This is polarization.

This is why a charged balloon can stick to a wall (but not a metal doorknob).

Wrap-Up: Did we meet our objectives?

Understand the basic properties of electric charge.

Differentiate between conductors and insulators.

Distinguish between charging by contact, charging by induction, and charging by polarization.

Homework

p. 633 #1, 3-5