1. Voltage And you

2. A small positive test charge (q o ) would move from point A to B * F = E q o + (parallel to F = ma) to move q o from B to A q o pt. A would require work (W = fIId) q o has more EPE than q o f q o f pt.B ΔEPE b-a /q o = -W/q o = J/C = Volt = electric potential (potential difference, electromotor force, EMF)

3. SO VOLTAGE IS: A measure of the difference in electric potential at 2 separate points (or terminals on a battery) This electric potential is transformed into other forms of energy (kinetic, heat, light) If charges flow then potential can equalize

4. Battery example: ++ charges not equalized = ++ Potential difference present ++ therefore voltage present + + charges equalized = + + no potential difference + + = no voltage

5. VDG Demos Pie plates Florescent tube Grounding apparatus Student circuit – insulate and charge entire group – then ground to water faucet Feel the flow of charges

6. What can be done with voltage All electronic devices transform EPE into other forms of energy – through the movement of charges (light, heat, magnetic fields)

7. EX: Transatlantic cable – Morris code communications When the war of 1812 treaty was signed in Europe, the fighting did not stop across the Atlantic for weeks – because there was no way to communicate ~ 1850 work began on first transatlantic cable Very heavy and thick – problems with breaking, sinking to bottom of ocean

8. Lab 15 Making the Pasco system work is most difficult part – problem solving focus!!! Make certain that your sensor is correct – and input is correct You can change the scale on the graph Now work on the lab please

9. POST LAB Battery voltage has no voltage oscillations = DC = direct current In series has additive effect on voltage Analogue signal – waves moving through the air – sensor changes to volts = oscillates hundreds of times per second 20Hz – 20,000 Hz = good hearing High frequency used in malls to keep kids away

11. Parallel charged plates direction of field direction of e- motion Battery ++++++++++++++ ++++++ + * e- will accelerate through 1.5V hole = particle accelerator - * EPE e- = qV = 2.4 E -19 J e- * ΔEPE = KE = ½ mv 2 - - - - - - - - - - - - - - - - - - - - - * v ~ 7 x 10 5 m/s Recall q e- = 1.6 x 10 -19 J If V = 1, then EPE e- = 1.6 x 10 -19 J = 1 electron Volt (eV) = unit of Energy

12. Back to the Voltage Basics A + chg. accelerates from region of high electric potential (voltage) to regions of low electric potential. A – chg. Accelerates from regions of low to high electric potential

13. Voltage and EPE are measureable only in terms of work – one point relative to another point (just like GPE at one height is relative to GPE at an arbitrary zero point)

14. Voltage equation summary: V = Joules/Coulomb = ΔEPE b-a /q o = - W/q o = F II d /q o = E q o d / q o = Ed = KQ /r * you would use this last one if calculating the electric potential at a point near a point charge NOTE: not the absolute value of Q

15. Finally The total electric potential (V) at a given location due to 2 or more charges is the algebraic sum of the potential due to each charge This will be important when you do the chapter 19 homework #13, 24, 36