theorems

Question 1

what are voltage sources

Answer 1

ideal sources in series with sources resistance
- internal resistance is 0, source reduce to ideal 1

Question 2

what are current sources

Answer 2

ideal source with a parallel source resistance
- when source resistance is infinite, current source is ideal

Question 3

how are voltage source and current source related

Answer 3

Is = Vs / Rs
Vs = Is x Rs

Question 4

what is the superposition theorem

Answer 4

• current/voltage in any given branch of a multi-source linear circuit can be found by determining the current/voltage in the particular branch produced by each source acting independently with all other sources replaced by internal resistance
• total current/voltage for the branch is the algebraic sum of the responses in that branch
• take 1 source at a time and sum the results

Question 5

what is Thevenins theorem

Answer 5

any 2 terminal resistive circuit can be replaced with a simple equivalent circuit when viewed from the 2 output terminals

Vth = the open circuit voltage between the two output terminal

Rth = the total resistance between the two output terminals when all sources have been replaced by their internal resistance

Question 6

how to calculate thevenins theorem (Rth & Vth)

Answer 6

• open the 2 terminals
• determine vth across the terminals
• determine rth across the terminals with all sources replaced by their internal resistance (ideal values)
• connect vth & Rth in series
• replace load across the terminals & calculate load Q & V using ohms laws

Question 7

what is nortons theorem

Answer 7

any 2 terminal resistive circuit can be replaced with a simple equivalent circuit when viewed from output

IN & RN in parallel

IN - the output current when the terminals are shorted
RN - total resistance appearing between the 2 outputs terminals when all sources have been replaced by internal resistance

Question 8

how to calculate Nortons theorem

Answer 8

• open the 2 terminals
• short the 2 terminals between the ones you want
• determine IN between the shortened terminals
• determine RN between 2 open terminals with all sources replaced with internal resistance
• connect IN & RN in parallel

RT = R1 + (R2xR3 /R2 +R3)
IT = Vs/RT -> IN = (R2/R2 +R3) x IT

Question 9

what is the maximum power transfer theorem

Answer 9

• used when you need to know the value of a load a which the most power is delivered from a source
• for a given source voltage, maximum power is transferred from a source to a load when the load resistance is equal to internal source resistance
• maximum power occurs whens RL =Rs

current source : a device that ideally provides a constant value of current regardless of load

Question 10

what is lenz law

Answer 10

when the current through a coil changes, an induced voltage is created across the coil that always opposes the change in current