Electrical Engineering

Fundamentals

Viktor Hacker, Christof Sumereder

• Publisher: De Gruyter Oldenbourg
• Year: 2020
• ISBN:
  9783110521139
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Fundamentals of Electrical Engineering is an excellent introduction into the areas of electricity, electronic devices and electrochemistry. The book covers aspects of electrical science including Ohm and Kirkoff's laws, P-N junctions, semiconductors, circuit diagrams, magnetic fields, electrochemistry, and devices such as DC motors. This text is useful for students of electrical, chemical, materials, and mechanical engineering.

1 The basic physic principles and definitions

1.1 The simple circuit

In everyday life, people do not distinguish between technically correct designations for electric quantities but abbreviate and incorrectly name it “electricity”. Colloquially, the expression “electricity bill” is used, when in reality the electrical energy consumption is meant; when an electrical accident happens, it is referred to as “electric shock”.

A person with technical knowledge is aware that a flow of an electric charge is designated “electric current” and that the physical quantity of current (intensity) uses the unit ampere. Furthermore, an expert knows that it is the voltage (measured in volts) that drives the current and that resistance (measured in ohm) at constant voltage determines the current (Figure 1.1).

To better understand the correlation between electric current, voltage and resistance, we look at the water cycle as analogue to the electric circuit.

Figure 1.1: Correlation between current, voltage and resistance.

Table 1.1:Water cycle as analogue to electric circuit.

Water cycle (analogue)	Electric circuit
Figure 1.2: Closed water cycle.	Figure 1.3: Closed circuit.
The flow of water $\frac{{\displaystyle Q}}{{\displaystyle t}}$is caused by the pressure difference $\mathrm{\Delta }P$ generated by pump P.	The current flow is caused by the potential difference (= voltage $V$) generated by the voltage source.
The pressure difference $\mathrm{\Delta }P$ determines the amount of water pumped via the load per time.	The potential difference (voltage $V$) determines the electric charge per time (current I) flowing through the load.
The pressure loss due to the resistance in the container $C$ is as high as the pressure difference $\mathrm{\Delta }P$ generated by the pump.	The voltage loss on the resistance $R$ is as high as the generated voltage $V$.

Considering this, it becomes apparent that

• a higher voltage with constant resistance causes a higher electric current and this correlation is linear³: $V\sim I$ → $I\sim V$
• a higher resistance with constant voltage causes lower electric current and the correlation is once again linear: $R\sim \frac{1}{I}$ → $I\sim \frac{1}{R}$

Combining these two aspects directly leads to Ohm’s law: $I=\frac{V}{R}$

1.1.1 The schematic diagram

The schematic diagram (see Figure 1.4) is a graphic representation of an electric circuit widely use...