1. Principles of Physics

2. So far, we’ve talked about non-moving charge We know that charged objects :  exert an electrostatic force on each other  move when the force is unbalanced  gain and lose energy as they move toward and away from other charged objects  Moving toward a like charge → increase in PE  Moving away from like charge→ decrease in PE We also know that a voltage exists between charged objects

3.  Charged objects are not useful unless moving  They move if there is a voltage Circuit A system in which charged objects move in response to a voltage source Must include:voltage source (battery) closed path for charges to follow (wires) method of controlling rate of flow (resistor)

4. Current (I): flow of electrons (negative charge)  In circuits charge is moving in solid materials (copper wires)  Only electrons can move in solids (Positive charge may flow in liquids or gases)

5. Current/electron flow is calculated by I = Current q = charge (C) t = time (s) Current units: 1 C/s = 1 Ampere = 1 Amp = 1 A I = q t

6. Voltage supply (power supply) Resistor Wire -+-+

7. Electrons flow from the negative side of the voltage supply (the short side) Conventional current flows from the positive side of the voltage supply (the long side) -+-+

9. Junction: where multiple wires (paths) meet All current flowing into a junction = all current flowing out of a junction. 1.5 A 1.0 A 2.5 A 3.0 A Current flowing in: 1.5 A + 2.5 A = 4 A Current flowing out: 3.0 A IN = OUT *Always add x to the side with less current 4 A = 3.0 A + x

10.  When one electron leaves from the negative side of the voltage supply another one enters the positive side  The rate that electrons leave is current  How fast they leave depends on resistance in the circuit

11.  A material with high resistance typically causes the electrons to experience more collisions as they move through

12. RESISTOR

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14. Resistance, R, is related to: Type of material Some materials have more resistance than others Length Electrons will experience more collisions as they travel through the longer resistor Cross sectional area Increasing cross sectional area decreases resistance because more electrons can get through at one time Temperature In metallic conductors, as temperature increases, resistance increases