Blog 5. Note: Resistance - Ohm's Law.

flow in a circuit depends on two things (characteristics):

• the amount of push
  

• the nature of the pathway

RESISTANCE: the opposition to flow.
The more difficult the path, the more opposition to the flow.

R = V/I, a ratio called 'Ohm's law'

R --> volts per ampere = Ohm
V --> volts
I --> current --> Amperes

The resistance of a conductor depends on:

• length
• cross-sectional area (thickness)
• material its made of
• temperature

Factor	Description	Proportionality
Length	The longer the conductor, the greater the resistance.	If length is doubled, resistance is doubled. R1 / R2 = L1 / L2
Cross-sectional area (thickness)	The thicker the conductor, the less the resistance.	If thickness is doubled, resistance is ½ original. R1 / R2 = A1 / A2
Type of Material	The general measure of resistance of a substance = Resistivity (unit: Ω · m)	If resistivity (p) is doubled, resistance is doubled. R1 / R2 = P1 / P2
Temperature	Greater molecular motion @ higher temperatures tend to ↑ resistance.	↑ in temp. of the conductor usually ↑ in the resistance, but not for all substances.

SUPERCONDUCTIVITY - ability of a material to conduct energy w/o heat loss due to electrical resistance.