Topic 2 & 3

Question 1

What is a branch?

Answer 1

A single element, e.g. a voltage source or resistor

Question 2

What is a node?

Answer 2

The point of connection between two or more branches.

Question 3

What is a loop?

Answer 3

Any closed path in a circuit.

Question 4

What is a mesh?

Answer 4

A loop with no other loops within it.

Question 5

What do nodes have to do with series?

Answer 5

If two or more elements exclusively share a single node, they are in series and carry the same current.

Question 6

What do nodes have to do with parallel?

Answer 6

If two or more elements are connected to the same two nodes, they are parallel, and share the same voltage.

Question 7

What is resistance?

Answer 7

The ability to resist current.

Question 8

How do you calculate resistance of a material?

Answer 8

Where R is resistance, p is the resistivity of the material measured in ohm metres, l is the length of the material, and A is the cross section area.

Question 9

What is Ohm’s Law?

Answer 9

The voltage across a resistor is directly proportional to the current flowing through the resistor. The constant of proportionality is R (resistance).

Question 10

What is a nonlinear resistor?

Answer 10

Unlike linear resistors, they do not obey Ohm’s law, as their resistance varies with current. E.g. Lightbulbs, diodes.

Question 11

What is the pronumeral denoting conductance? (Not unit)

Answer 11

G. Conductance is measured in mhos (Ʊ) or Siemens (S).

Question 12

How do you represent power in terms of resistance?

Answer 12

Question 13

What is KCL?

Answer 13

Kirchhoff’s current law, stating the sum of currents entering a node is equal to the sum of currents leaving the node.

Question 14

KCL current sign convention

Answer 14

Currents entering the node are positive, while currents leaving are negative.

Question 15

What is KVL?

Answer 15

Kirchhoff’s voltage law states that the sum of all voltages around a loop is zero. Sum of all voltage drops = sum of all voltage rises (In a loop)

Question 16

Important rules to avoid violating KCL and KVL?

Answer 16

A circuit cannot contain two different currents in series or two different voltages in parallel.

Question 17

What is the Req (equivalent resistance) of resistors in series?

Answer 17

They can be simplified into a single resistor with the sum of all of their resistances.

Question 18

What happens to Req (equivalent resistance) with short circuits?

Answer 18

In a short circuit, the current will flow through the smallest resistance.

Question 19

What happens with Req (equivalent resistance) with an open circuit?

Answer 19

Current will flow through the path with the lowest resistance.

Question 20

What is circuit ground?

Answer 20

Voltage is a differential quantity, it is a relative, so you need a reference node. This is referred to as the circuit ground, usually 0 Volts.

Question 21

How do you calculate the voltage across each resistor in series?

Answer 21

Where vn is the voltage across the resistor of interest, Rn is the resistance of the resistor, v is the input voltage and Req is the sum of all resistances.

Question 21

What is the proportionality between resistances of resistors and the voltage drop across them?

Answer 21

The larger the resistance, the larger the voltage drop.

Question 21

What is Req (equivalent resistance) of parallel resistors? Also fact about Req?

Answer 21

Req is always smaller than the resistance of the smallest resistor.

Question 21

What does the principle of current division state about currents flowing through larger and smaller resistances?

Answer 21

More current flows through smaller resistances.

Question 22

How do you calculate current across resistors in parallel?

Answer 22

Question 23

Voltage and current over nodes and meshes?

Answer 23

The voltage across a node is uniform. The current through a mesh is uniform.

Question 24

Positive and negative terminal of a diode?

Answer 24

Anode and cathode

Question 25

What is superposition?

Answer 25

States that the voltage/current through an element in a linear circuit is the sum of all the contributions of each independent source to the variable.

Question 26

What must be kept in mind when applying superposition principle?

Answer 26

1. We consider one independent source at a time while all others are turned off. (All voltage and current sources are 0.) 2. Dependent sources are left alone as they are controlled by circuit variables.

Question 27

Why can't superposition be applied to calculating power?

Answer 27

It is only applicable to linear responses. Power is a non linear response, as it is a quadratic.

Question 28

What is source transformation?

Answer 28

Transforming a voltage source in series with a resistor with a current source in parallel with a resistor. And the other way around.

Question 29

What does source transformation state about Req and the switching between voltage and current?

Answer 29

States that: - If we turn off all the sources, the Req must be the same. - The current and voltage are related by Ohm's law.

Question 30

What is Thevenin's theorem?

Answer 30

Basically any linear two-terminal circuit can be replaced by a voltage source (Vth) in series with a resistor (Rth).

Question 31

Second method of obtaining Rth + Required conditions.

Answer 31

Works for a circuit with both indep and dep, but can't work for a circuit with only dependent sources. Rth is equal to open circuit voltage/short circuit current. Vth/isc. To get short circuit current, connect a-b, and measure the current.

Question 31

First method of obtaining Rth. Required conditions

Answer 31

Only works if all sources are independent. Rth can be measured when all sources are turned off (voltage source = short circuit, current source = open circuit). Rth is then just Req.

Question 31

What is Vth?

Answer 31

Vth is equal to the voltage as if there was an open circuit across the terminals of the load.

Question 32

Third method of obtaining Rth + Required conditions

Answer 32

Always valid. Turn off all independent sources and attach a voltage source (vo) to the terminals +a,-b and find the current. Or, attach a current source (io) and find the resulting voltage. For simplicity, set vo/io = 1V/A.

Question 33

What is the Vth of a dead network?

Answer 33

Question 33

What do we call a circuit with only dependent sources? What is its property?

Answer 33

We call it a 'dead network'. As there are only dependent sources, all voltages and currents are zero.

Question 34

What is Norton's theorem? What is In equal to?

Answer 34

The dual form of Thevenin's. It states that any linear two-terminal circuit can be replaced by a current source (In) in parallel with a resistor (Rn)

Question 35

What is the maximum power than can be transferred to a load?

Answer 35

When the resistance of the load is equal to the Thevenin resistance, then you apply this equation.