Physics Announcements WebAssign – –Chapter 22 due next Wednesday Exam #2 corrections still not graded Exam #3 is on April 9

Class Schedule 3/19Chapter 10Projectile and Satellite Motion (Pg ) 3/21Chapter 11Atomic Nature of Matter (Pg ) 3/26Chapter 22 Electrostatics, Part 1 (Pg ) 3/28Chapter 22Electrostatics, Part 2 (Pg ) 4/2Chapter 23Electric Current, Part 1 (Pg ) 4/4Chapter 23Electric Current, Part 2 (Pg ) 4/9Midterm Exam #3

Chapter 22 Electrostatics, Part 2 Charge Polarization Electric Field Electric Potential Electric Charge Storage

Charge Polarization A charge can be induced in a conductor by bringing another charged object close by: This is because charges are free to move around in a conductor. In an insulator, charges aren’t free to move around, so when a charged object is brought near, the charges within the insulator’s atoms and molecules get redistributed: Charged rod Metal sphere Insulator atom + - More accurately, the centers of charge are moved so that one side of the atom is more positive, the other side is more negative. The atom becomes electrically polarized. Examples: A comb and paper A balloon and the wall.

Electric Field We know that a force acts between charges – the “Coulomb Force” This force acts even though the objects aren’t in contact, and extends through all space … just gets weaker as you move away from the charged object. The force field due to a charged object exists in the space around it regardless of whether another object is there to “feel” it (just like gravity).. And it’s called the “Electric Field”. The field acts in the direction that a positive “test” charge would be pushed. +- Field due to a positive charge Field due to a negative charge See text pg 423 for pictures of some example electric field diagrams.

Electric Shielding The electric field on the inside of any conductor is zero, regardless of how large the field is on the outside. The field strengths due to all the charges on the outside of the conductor cancel each other on the inside, making the field inside completely zero. Shape and size of the conductor don’t matter.

Electric Potential Recall that gravitational potential energy depended on position of a mass in a gravitational field. Similarly, the potential energy of a charge depends on its position in an electric field. We call this its Electric Potential Energy. The electric potential energy per unit charge is the Electric Potential. The voltage in your wall plug is an indication of the energy that each electron has as it goes through your house. The “120V” electric potential of your outlets means there is that much potential difference between the sides of the plug.

Question 1 How much energy is give to 1 Coulomb of charge flowing through a 1.5 Volt battery? A.400 Joules B.25 Joules C.1.5 Joules D.1.9 billion Joules

Electric Energy Storage Electric energy can be stored in a device called a Capacitor Air Or Other insulator conductors The plates of the conductors are charged, then the wires are disconnected, leaving the charges on the plates. The electric energy is stored in the field between the charged plates. A Van de Graaff Generator is another way to store electric energy.