» Named for Georg Simon Ohm (1789-1854)

𝑽 = 𝑰𝑹, where V is voltage, R is resistance and I is current

*only holds when Resistance is independent of Voltage

Not a fundamental Law, meaning it only holds under certain conditions

» Ohmic: follows Ohm’s Law, using the equation the resistance of a circuit can be calculated using voltage and current

» Non- Ohmic: does not follow Ohm’s Law, equation does not work due to variable resistance that is dependent upon voltage

As current I flows through a given element in a circuit it loses voltage V in the process

» This power dissipation is found using equations:

P = I × V

or

P = I 2× R˃ Unit : Watts

Resistance: the opposition to the flow of current in an electrical wire or element

˃ Think “friction”

˃ Symbol: R

˃ Unit : Ω (Omega) Ohm, equivalent to 1V/1A

˃ Equation: 𝑹 =𝑽

𝑰

Equivalent Resistance: total resistance of a circuit based on number of components and their configuration (series or parallel)

» Series Rule: 𝑹𝑻𝒐𝒕𝒂𝒍 = 𝑹𝟏 + 𝑹𝟐 + 𝑹𝑵

» Parallel Rule: 𝟏

𝑹𝑻𝒐𝒕𝒂𝒍=

𝟏

𝑹𝟏+

𝟏

𝑹𝟐+

𝟏

𝑹𝑵

NOTE: Rules only work when circuit, or portion of a circuit are only series or only parallel

» Resistance is Dependent Upon:

˃ Length of wire/element: longer = ↑ resistance

˃ Cross-sectional area of wire/element: larger= ↓ resistance

˃ Material type: copper vs aluminum, etc.

˃ Temperature: decrease in temperature= ↓ resistance

» Gustav Robert Kirchhoff, German Physicist (1824 –1887)

» Credited with two laws essential to understanding circuits.

1. Kirchhoff's Junction Rule

2. Kirchhoff’s Voltage Rule

Rule: At any node (junction or branch point) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node

» The algebraic sum of voltages around each loop is zero

˃Beginning with one node, add voltages across each branch in the loop (if you encounter a + sign first) and subtract voltages (if you encounter a – sign first)

» Σ voltage drops - Σ voltage rises = 0

» Or Σ voltage drops = Σ voltage rises

10 V

6 V

4VLoop #1 Loop #2

Loop #3

Loop #3

4V

» Notes Circuit Resolution