Question: What does a "dead circuit" in Thevenin's and Norton's theorem mean?


Answer:

A "dead circuit" means that all independent sources have been zeroed out. Zeroing out a source means that independent voltage sources are converted to short circuits while independent current sources are converted to open circuits.

Question: What technique is applied to convert a Thevenin equivalent circuit into a Norton equivalent circuit or vice versa?


Answer:

Source transformation is applied. A voltage source in series with an internal resistance is equivalent to a current source in parallel with the same internal resistance.

V thevenin = (I norton) x (R internal)
I norton = (V thevenin) / (R internal)
R internal = (V thevenin) / (I norton)

Question: How many responses are obtained from an N number of independent sources present in a given circuit?


Answer:

N responses are obtained from an N number of independent sources.

Implication of a negative response in superposition

Question: What does a negative response in superposition imply?


Answer:

A negative response implies that the original assumed direction of current or polarity of voltage should be reversed.

Mesh and Nodal Analysis Principles

Question: What basic laws are the underlying principles of Mesh Analysis and Nodal Analysis?


Answer:

Kirchoff's Voltage Law (KVL) is the underlying principle used in Mesh Analysis.

Kirchoff's Current Law (KCL) is the underlying principle used in Nodal Analysis.

Implication of a negative mesh current

Question: What does a negative mesh current imply?


Answer:

A negative mesh current implies that the original assumed direction of current is wrong and is in the reverse direction of the actual current.

Maximum Power Transfer in DC Circuits

Question: When is the maximum power delivered from a practical source to a load?


Answer:

Maximum power is delivered to the load when its resistance is equal to the source's internal resistance.

Ideal current source resistance

Question: How much internal resistance does an ideal current source have?


Answer:

An ideal current source has infinite resistance.

Ideal voltage source resistance

Question: How much internal resistance does an ideal voltage source have?


Answer:

An ideal voltage source has zero resistance.

Current for full scale deflection

Question: What current is required for full scale deflection of a galvanometer having a current sensitivity of 50 micro-amperes per scale division? The meter has exactly 50 divisions on either side of the mid-scale index.


Answer:

There are two possible interpretations of the problem. One has a meter having a mid-scale index value of zero, a maximum positive current reading, and a maximum negative current reading.

To solve for the maximum positive value of current that will cause full scale deflection, simply multiply the current sensitivity by the number of divisions. In this case, 50 micro-amperes per scale division multiplied by 50 divisions will give 2500 micro-amperes or 2.5 mA.

The other interpretation is that a meter can read from zero to a maximum positive value of current, and that there are 100 divisions in between these two extremes. In this case, 50 micro-amperes per scale division multiplied by 100 divisions will give 5000 micro-amperes or 5 mA.

Computing the value of a shunt resistor

Question: Determine shunt resistance needed to convert a galvanometer to an ammeter with a full scale reading of 10 A if the scale requires 2.5 mA to cause full scale deflection with a coil resistance of 10 ohms?

Answer:

I original meter max = I full scale deflection = 2.5 mA
Using the current divider principle:
(I original meter max)/(I adjusted meter max)=(R shunt)/(R meter + R shunt)
(25 mA) / (10 A) = (R shunt) / (10 ohms + R shunt)
R shunt =  0.0251 ohms

Computing the value of a series resistor

Question: Determine series resistance needed to convert a galvanometer to a voltmeter reading 15V on full scale deflection if a current of 2.5 mA causes full scale deflection and the resistance of the coil is 10 ohms?

Answer:

V original meter max = (I full scale deflection) x (R meter) = (2.5 mA) x (10 ohms) = 25 mV
Using the voltage divider principle:
(V original meter max)/(V adjusted meter max)=(R meter)/(R meter + R series)
(25 mV) / (15 V) = (10 ohms) / (10 ohms + R series)
R series =  5990 ohms

How to create a wattmeter

Question: What type of basic meters can be configured as a wattmeter?

Answer:

A wattmeter measures power. Since power is the product of voltage and current, if we have a voltmeter and an ammeter available, these basic meters can be configured to measure power. The ammeter will be connected in series to the circuit element while the voltmeter is connected in parallel to the circuit element.

Why a voltmeter is a high resistance instrument

Question: Why is it necessary that a voltmeter be a high resistance instrument?

Answer:

Since a voltmeter is connected in parallel to a circuit element, it should have a high resistance to prevent current passing through the circuit element from passing through it instead. This ensures an accurate voltmeter reading.

Why an ammeter has low resistance

Question: Why is it necessary that an ammeter be a low resistance instrument?

Answer:

Since an ammeter is connected in series to a circuit element, it should have a low resistance to avoid adding to the resistance of the circuit element. This prevents deviations in the value of the current being measured and ensures an accurate meter reading.

Use of a Series Resistor

Question: What device is used to extend the range of a DC voltmeter and how is it connected to the basic meter?


Answer:

A resistor connected in series to the voltmeter can be used to extend the voltmeter's range.

Use of a Shunt Resistor

Question: What device is used to extend the range of a DC ammeter and how is it connected to the basic meter?


Answer:

A resistor connected in parallel or shunt to the ammeter can be used to extend the ammeter's range.

Meter Movement

Question: Describe the type of movement used in analog meters

Answer:

The D'Arsonval movement is a DC moving coil-type movement commonly used in voltmeters, ammeters and ohm meters. An electromagnetic core is suspended between the poles of a permanent magnet as seen in the image below.

In an ammeter, current passes through the coils of the electromagnet (current path not shown in the figure). This current produces a magnetic field that opposes the magnetic field already set up by the permanent magnet in the figure. The stronger the current, the stronger the magnetic field, and the larger the pointer deflection. If current is no longer flowing, the upper and lower control springs will bring back the pointer to its default position for a zero current reading.