2. Electrical Fundamentals

Question 1

what is an ideal current source

Answer 1

source that can apply any voltage while maintaining a constant current from its terminals

Question 2

for a power source, the arrows for voltage and current are

Answer 2

in the same direction

Question 3

what is an ideal voltage source

Answer 3

one that can supply any current while maintaining a constant voltage across its terminals

Question 4

what is the terminal characteristic of a battery

Answer 4

the graph of battery voltage versus battery current; a negative slope due to internal resistance

Question 5

what is a load?

Answer 5

device or circuit connected to the output of another circuit

Question 6

in a series circuit with 10 and 20 ohm resistors, which resistor draws a larger load?

Answer 6

10 ohm resistor as it draws a larger current/ higher power dissapation (this is the definition of load)

Question 7

A good test for sensibility when calculating resistance values in series and in parallel is

Answer 7

Series: total resistance larger than largest individual
Parallel: total resistance smaller than smallest individual

Question 8

What is the difference between a node and an essential node?

Answer 8

A node is a point where two or more circuit elements join, whereas an essential node is a point where THREE or more circuit elements join

Question 9

What are the four key steps in node-voltage analysis?

Answer 9

1. Select one of the essential nodes to be the reference/ground point (zero voltage), marking it with an earth symbol
2. Define voltage(s) for remaining essential nodes (e.g label ‘V1’)
3. Write node-voltage equation for each of the essential nodes in step 2 (total current leaving node=0)
4. Solve the node-voltage equations simultaneously

Question 10

Law of superposition

Answer 10

The total response of a circuit is the sum of the responses that occur when the current and
voltage sources are considered one at a time while setting all the other sources to zero.

Question 11

In superposition, to set a current source to zero:

Answer 11

replace with open circuit

Question 12

In superposition, to set a voltage source to zero:

Answer 12

replace with short circuit (ie replace with wire)

Question 13

What is a Thevenin equivalent circuit?

Answer 13

a circuit consisting of an ideal voltage source in series with a resistance, equal in output current and voltage to the original

Question 14

Find Thevenin resistance

Answer 14

setting all current and voltage sources to 0, then calculating the resistance “looking back” into the terminals