Warm Up 3.17.2014 3.18.2014 What is an electron? What charge does it have? What is a proton? Which move easier between atoms, electrons or protons? Note: To be graded, warm ups need to be dated. The questions should either be written into your notebook or rephrased into sentences with your answer.

Electric Charge March 17 & 18, 2014

Electric Charge What does it mean for an object to have an overall electric charge? Either the object has lost or gained electrons. If an object has gained electrons it is now negative. Why? If an object has lost electrons it is now positive. Why?

The Structure of the Atom Recall from Chemistry what happened when atoms lost or gained electrons. An atom that loses an electron becomes a cation. It now has more PROTONs than electrons and is now POSITIVE. An atom that gains an electron becomes an anion. It now has more ELECTRONs than protons and is now NEGATIVE.

Charge Interactions We’ve all heard the phrase “opposites attract.”

What about alike charges?

Interactions with Neutral Objects What type of interaction will a charged object have with a neutral one? It turns out, any charged object will attract a neutral one. Confusing huh? Let’s look at why.

Interactions with Neutral Objects Neutrally Charged Balloon Neutrally Charged Wall

Interactions with Neutral Objects Negatively Charged Balloon Neutrally Charged Wall

Interactions with Neutral Objects Negatively Charged Balloon Neutrally Charged Wall

Measuring Electric Charge What units do we use to describe charge? The Coulomb, with the unit symbol C. 1 C of charge = 6.241 x 1018 electrons

Coulomb’s Law There is very clearly a force that exists between two charged objects. How do we define it? Recall the gravitational force between two objects.

Coulomb’s Law The force that exists between two charged objects is called the electrical force. (Fe) It has units of Newtons. kc is known as the Coulomb’s Law constant

Example A charge of -2.0 x 10-6 C and a charge of +3.0 x 10-6 C are 0.50 m apart. What is the electrical force between them?

Fe is a vector Recall that force is expressed as a vector. It has size AND direction. A Fe that is negative indicates an attractive electrical force. A Fe that is positive indicates a repulsive electrical force.

The Inverse Square Law Doesn’t this pesky inverse square thing go away? If the distance between two charges doubles, what happens to the force between them? If the distance between two charges is cut in half, what happens to the force between them? Force (N) Distance (m)

Electrostatics Quantity Chart Symbol in Formula Unit Unit Symbol Charge q Coulombs C Potential Difference V Volts Voltage Current I Amperes or Amps A Resistance R Ohms Ω Power P Watts W Electrical Force Fe Newtons N