3a. Circuits KCL, resistors

Question 1

How can we mathmatically model our electrical devices?

Answer 1

Break them down to only consider p.d. and current in and out of each electrical device in a system.

Question 2

What is a resisitor and how does it work?

Answer 2

Resistors: resist the flow of energy. Requires a voltage flow through it.

Works by causing vibrations on nuclui, reducing the current flow.

It follows ohm’s law: V = IR, R = V/I.

Power = IV = I^2R = V^2/R

Question 3

What is the equation for resistance, ρ?

Answer 3

R = ρL / A = L/σA

Where ρ = resistivity, σ = conductivity.

Question 4

State Kirchov’s Current Law, KCL

Answer 4

KCL: The sum of the currents into a node is zero

Question 5

What are the equation for finding Total resistance in series and parrallel?

Answer 5

In Series:
Rt = R1+ R2 + … + Rn

In parrellel:
1/Rt = 1/R1 + 1/R2 + … + 1/Rn
for 2 parallel resistors: Rt = R1R2 / R1 + R2.
Resistors in paralell will always combine to create a smaller resistance than either of the individual ones.

Question 6

What are Nodes / Ground?

Answer 6

• Nodes have a specific voltage with respect to ground. They can move along a wire, and the voltage will be the same, assuming wires have zero resistance, and it doesn’t pass through a component.
• Ground is a reference point usually.
• Nodes can be found and unique in different wires, one might be zero like ground while other range between components

Question 7

How do we define series and parallel resisters?

Answer 7

• Series: each resistor in chain shares a central node with notheing else that draws current (so current is same in all resistors).
• Parallel: they all start and end at the same pair of nodes (so same voltage across).
• Examples below:

Question 8

True or false:

Resistance doesn’t vary with temperature

Answer 8

Fasle, they do in elements vary with temp. This is why we have themoristors.

Question 9

What is a short-circuit?

Answer 9

A wire that joins two parts of the circuit together with zero resistance.