Physics Unit 2 Electricity and Circuits

Current

Measure of amount of charge moving per second (in Amperes/A)

e- usually drift in a random direction with no net movement of charge

Current Formula

I(A) = change in charge (Q, Coulombs)/change in time (t, seconds)

Potential Difference

When a potential difference is applied across a conductor, current is produced, causing a net movement of charge rather than a rapid flow

Conventional Current

Current being drawn flowing in the opposite direction although electrons flow from a circuits negative terminal to its positive one

Voltage

Potential Difference, measure of the energy given to current carriers (Volts)

Voltage Formula

V = Work (Joules)/Charge (Coulombs)

difference in potential between 2 points, must connect a voltmeter in parallel

Resistance

Measure of the opposition a material exerts against the flow of electrons

Resistance Formula

R (Ω) = V (Voltage)/I (Current)

Voltage/Current Graph for Resistor (Ohmic)

Linear Graph
R is Constant, meaning it is Ohmic
Metals are ohmic resistors

Voltage/Current Graph for Non-Ohmic Device

Curved Graph
Not constant
Non-Ohmic

Series Circuit

All elements arranged in same path
Current is same across circuit
Voltage is different across resistors, total is same (it adds up)

Parallel Circuit

Elements connected across multiple branches
Resistors receive same Voltage
Current is different, it splits at each junction

Resistance using Resistivity

R = (p) L/A

p = Resistivity
L = Length (m)
A = Area (m²)

Factors affecting a Substance’s Resistance

• Cross-sectional area: larger cs A = lower resistance

  • ex. for a wire it is a circle (cylindrical shape face)

• Length

  • Length of a conductor is proportional to resistance

• Material

  • Resistivity changes depending on material used as conductor for electricity

  • lower resistivity = better conductor