# Lecture 1 - Resistors

- Created by: Jeeves3865
- Created on: 03-10-20 11:28

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- RESISTOR, RESISTANCE + BASIC ELECTRONICCIRCUITS
- KIRCHOFF'S LAWS
- CURRENT LAW
- "Sum of currents in a network of conductors meeting at any node = ZERO."
- I1 + I2 + I3 + I4 = 0

- VOLTAGE LAW
- "Sum of all voltage drops + sources around any loop = ZERO."

- CURRENT LAW
- RESISTIVITY
- Resistance of an ohmic conductor...
- Proportional to LENGTH
- Inversely proportional to CROSS SECTIONAL AREA

- Resistivity = Resistance x cross-sectional area / length

- Resistance of an ohmic conductor...
- VOLTAGE DROP + CURRENT
- Current PROPORTIONAL to VOLTAGE.

- RESISTANCE
- Resistance = Voltage / Current
- R = V / I

- Ohm's Law
- Voltage = Current x Resistance
- V = IR
- R independent of V

- Collisions between electrons + fixed charges in material

- Voltage = Current x Resistance
- Units
- Volts per Ampere

- Admittance
- Reciprocal of resistance
- Y = 1 / R

- Reciprocal of resistance

- Resistance = Voltage / Current
- ORIGIN OF A MATERIAL'S RESISTANCE
- 1. Electrons move in conductor due to external potential
- 2. Electrons collide with the conductor's lattice
- 3. Energy lost and repeatedly re-accelerated by electric field
- 4. Collision process creates internal friction

- 3. Energy lost and repeatedly re-accelerated by electric field

- 2. Electrons collide with the conductor's lattice

- 1. Electrons move in conductor due to external potential
- RESISTANCES iN CIRCUITS
- SERIES
- Follows voltage law
- R = R1 + R2 + ... + Rn

- PARALLEL
- Follows current law
- 1/R = 1/R1 + 1/R2 + ... + 1/Rn

- Follows current law

- SERIES
- RESISTIVITY OF CONDUCTORS
- Good conductors = LOW resistivity
- Insulators = HIGH resistivity

- KIRCHOFF'S LAWS

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