Introto Circuit Analysis

Question 1

Define CA, DC, aims and relevance.

Answer 1

Direct current- constant, unidirectional flow of charge, Thomas Edison.
Alternating current- reverser direction at a constant frequency (50Hz in the Uk). Essential for designing efficient electrical systems, modern models combine DC and AC functions.

Question 2

Basic circuit concepts.

Answer 2

Electrical charge- electron as the unit of charge.
Electric field (E)- vector field, exerts force on charges. (+): sources, (-): sinks.
Voltage (V): how much potential energy per charge is available to move electrons between 2 points.
Current (I): rate of flow of charge
Resistance (R): opposition of flow to current. Dependant on material properties (resistivity, ρ) and geometry.

Question 3

Define Ohm’s law

Answer 3

V= IR, current through a conductor between 2 points, directly proportional to the voltage across 2 points, inversely proportional to resistance (R= ρL/ A), A- cross sectional area.

Question 4

What is power and how is it calculated

Answer 4

The rate of energy transfer, P= IV. In resistors power dissipated as heat- defined as P= I^2R. I

Question 5

What is passive sign convention PSC

Answer 5

Helps determine the direction of the current and voltage.
Resistor (passive element) absorbs energy when the current enters its positive terminal. Voltage sources, active elements generate energy.

Question 6

Resistors and conductivity

Answer 6

Metals- high conductivity, high conc. of free electrons.
Semiconductors have both electrons and holes as charge carriers, conductivity is modifiable by doping.

Question 7

What is ε and what is the formula

Answer 7

emf is the electromotive force, it’s the total voltage generated by a source when no current is flowing. It represents the energy supplied to each coulomb of charge as it moves through the power source.
V= ε- Ιr
r- internal resistance of source, I= current, V= terminal potential difference.
ε= V+ Ir

Question 8

What are the main equations for internal resistance

Answer 8

ε= V+ Ir
ε= I( R+r)

Question 9

Conventional current

Answer 9

Flow of positive charge- the movement of positive charge from positive to negative terminal of a power source. It is parallel to the applied E- field.

Question 10

How to find the power dissipated by a circuit

Answer 10

Pd= Pr1+ Pr2
Power dissipated by R1 and R2. Using Ohm’s law, power dissipated for each resistor:
P= I^2*R.