Something called "electric charge" exists on matter Something called "electric charge" exists on matter. We detect it's presence by attraction or repulsion to other "charge". Two kinds of charge: Positive - which we attribute to a deficit of electrons Negative - which we attribute to an excess of electrons "Electrons" are carriers of negative electric charge Like charges repel; unlike charges attract Charge is conserved in a closed system. The number of electrons always remains the same Conductors permit electrons to flow; Insulators inhibit the flow of electrons

What makes a good conductor? SHELL Sub shell Max # of electrons K s 2 L p 6 M d 10 Nickel Atom

Copper atom 29 Protons 29 Electrons 29 Neutrons

Let's introduce some definitions before we continue: to quantify "electric charge" we label the amount of charge on a body as: q q = quantity of electric charge We can have -q (negative charge) or +q (positive charge)

One Coulomb = 1.0 C = 6.242 x 1018 electrons We further define a basic unit of charge (just as we defined the basic unit of mass as a kilogram) as: the "Coulomb" One Coulomb = 1.0 C = 6.242 x 1018 electrons This means that a SINGLE electron carries a very small charge. Can you figure out how much charge (in "Coulombs") are on a single electron? -____________ C on 1 e- This number is a constant and a very important value. It also represents the charge on the PROTON ( but + )

Inside a thunderhead, electrical charges become separated Inside a thunderhead, electrical charges become separated. Warm updrafts sweep positive charges aloft, leaving the bottom of the cloud negatively charged. The attraction between the ground and the negative charges in the bottom of the cloud creates the lightning stroke, a brief current of negative charge that travels from cloud to ground. Typical current in a lightning bolt is 40,000 Amperes (that’s about 40,000 Coulombs per second) with a voltage of up to 100,000,000 volts.

- THE ELECTRIC FIELD + + + + + + + + + + + + + + + Between two charged bodies there is a force, F, of attraction or repulsion: + + + + + + + + + - + + + + + + A We don't understand why; we can only say this is what happens. We can think of a charged body as changing the nature of the space surrounding it.

The field gets weaker as we move away from the charge…it follows the “inverse square law” just as Gravitation did and just as our recent study of Sound Intensity showed. Why? + A

Direction of the Electric Field + Outward (away) from a positive charge These are called “field arrows” _ Inward (towards) a negative charge

We draw the number of arrows proportional to the charge…more charge, more arrows. Say the charges are in “mCoulombs” (that’s micro-coulombs, or 10-6 Coulombs) 6 12 ?

We draw the number of arrows proportional to the charge…more charge, more arrows. Say the charges are in “mCoulombs” (that’s micro-coulombs, or 10-6 Coulombs) +6 +12 -8 -10

When charges get near each other, these fields interact For unlike charges, the arrows go from the positive charge to the negative charge: +6 -4

For like particles the arrows are repelled: -4 -4 The field arrows never cross in either case

+ - k|q1q2| F = r2 Coulomb’s Law quantifies the attractive and repulsive behavior we observe in electrostatics Coulomb used a torsion balance (similar to the one Cavendish used to determine the gravitational constant) k|q1q2| r2 F = + - degrees of twist determines force

k|q1q2| F = r2 Force = Newtons q1 = charge on particle one (in Coulombs) q2 = charge on particle two (in Coulombs) r = distance between particles (in meters) k = 9 x 109 (N·m2)/C2 (Coulomb's constant)

SUPERPOSITION OF ELECTRIC CHARGE (super - pose: to place on top of; to add) The electrostatic force is additive q1 q2 q3 - + 1.0 m 1.8 m The force on this charge = force from q1 + force from q3 The force on this charge = force from q1 + force from q2

- + + 1.0 m 1.8 m q1 q2 q3 -1.3 x 10-6 C +2.3 x 10-6 C +1.8 x 10-6 C The force on this charge = force from q1 + force from q3 The force on this charge = force from q1 + force from q2 F = k|q1q2| / (r12)2 + k|q2q3|/ (r23)2 F = k|q1q3| / (r13)2 + k|q2q3|/ (r23)2 The subscripts on "r" refer to the particle distance; that is, r12 represents the distance between particles 1 and 2.

This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg) Just as we defined a gravitational field, we define an "electric field" in a similar manner: This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg)

This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg) Just as we defined a gravitational field, we define an "electric field" in a similar manner: This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg)

This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg) Just as we defined a gravitational field, we define an "electric field" in a similar manner: This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg)

This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg) Just as we defined a gravitational field, we define an "electric field" in a similar manner: This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg)

This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg) Just as we defined a gravitational field, we define an "electric field" in a similar manner: This is the gravitational field (Earth = 9.8 m/s2 or 9.8 N/kg)

The general equation for an ELECTRIC FIELD is: (compare this to the equation for the gravitational field)

Notice that for gravity, F = mg We see that in electrostatics, F = qE

Here’s our equations to date Here’s our equations to date. At first we will only deal with POSITIVE charges: Electric Field Force F = |q|E