Voltage And you

Every charge has an electric field Just like every mass has a gravitational field When the fields of 2 masses interact there is a force of attraction (Fg) When 2 electric fields interact, there is a electrostatic force! (Fele)

A small positive test charge (qo) would move from point A to B * Fele = E qo + (parallel to F = ma) q1 pt.A q1 has more EPE than q2 I would need to do work to move q2 pt.B the charge from pt. 2 to pt. 1

So if position 1 has more EPE than position 2 Then it has more Voltage!!! Volt = electric potential = J/C (potential difference, electromotor force, EMF) The gravity parallel is when I hold an object up higher in the air, it has more gravitational potential energy

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

Analogous to: A lake located at a high elevation that is connected to a lake at a low elevation There is the potential for water to flow because of the elevation difference. In a similar fashion charges have the potential to flow when there is a voltage difference (for example from one terminal of a battery to the other terminal).

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

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)

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 Use of voltage difference to transmit messages Very heavy and thick – problems with breaking, sinking to bottom of ocean

Voltage and Electric Potential Energy 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)

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 voltage to high electric potential (voltage)

Voltage equation summary: V = Joules/Coulomb R = resistance (ohms) I = current (amps) = Ohm’s law is: V = IR Show PHET battery simulation

Electrodynamics investigation introduction Flow of charges = current (I) = charge/time = Δq/Δt 1 coulomb/ 1 sec = Ampere (amps) Resistance (R) = voltage/current = V/I 1 volt/ampere = Ohm (Ω) That is to say, lg. V with small current = high resistance

DC = direct current (moves in same direction) AC = alternating current (changes directions)

Lab activity here…

Resistance in wires In a wire: R = ρ (L/A) ρ = resistivity of the material (Ω  meters) L = length, A = cross sectional area

POST LAB Battery voltage has no voltage oscillations = DC = direct current In series has additive effect on voltage