CHAPTER 16 Electric Charge and Electric Field

•In static electricity, electrons are transferred to an object and it is – while the other object becomes +

•Opposites attract…like charges repel.

•The law of conservation of electric charge states that the net electric charge produced in any process is zero.

16-2 Electric Charge in the Atom

• Atoms have electrons in an orbit or cloud.• When electrons are gained, an atom

becomes - …when electrons are lost, - a- makes a +.

• Molecules with two different charged ‘ends’ are polar molecules.

• Subtract electronegativities and greater than .4 = polar bond…two ends = a polar molecule.

16-3 Insulators and Conductors

• Conductors carry a charge easily.

• Insulators are nonconductors.

• Semiconductors are borderline or act like both conductor and insulator at different times.

• Free electrons are required for a substance to be a good conductor.

16-4 Induced Charge; the Electrosope

• See diagram p479 for charge by contact and by induction.

• An electroscope is a device used to measure or detect a charge.

• Electrometers are an electronic device that measures a charge.

16-5 Coulomb’s Law

• F=k (Q1Q2)/r2

• Charles Coulomb (1736-1806)• The Coulomb is the SI unit of charge.• k= 8.988x109(N.m2)/r2

• One electron = 1.602x10-19C• F=[1/(4o)] (Q1Q2)/r2

o=1/4k= 8.85x10-12C2/N.m2

• See Example 16-1 p483

HOMEWORK• P497 q1 and pr#1-8