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The electron is existentially indispensable. It is at the heart of chemical reactions; and the electrical energy that propelled humans into their unique technological sphere of influence. The electron will also play a fundamental role in homo -sapiens series' journey towards infinite intelligence.

Figure 7.7 is an electric circuit of a lab power supply put together in the TECTechnics Lab. Space of interest : S₇P₁A₁₃ (1' by 1' by 4" container)
(a) Define: (i) electricity (ii) voltage (iii) resistance (iv) electric circuit.
(b) Identify the components of the circuit and their respective functions in the circuit.
(c) What are the three primary stages of the circuit? What are the PjProblem Strings associated with each of the stages? Thus establish the PjProblem String Sequences of the lab power supply.

The strings: all PjProblems at play. However, the following PjProblemStrings are of primary interest:
S₇P₁A₁₄ (containership - volume)
S₇P₂A₂₁
S₇P₃A₃₂ - (force-push)
S₇P₄A₄₁ - (motion - linear)
S₇P₅A₅₁ - (change - physical)
S₇P₆A₆₅ - (grouping/interaction - physical)
S₇P₇A₇₂ - (equilibrium - dynamic)



(ai) Electricity is charge in motion. There are two types of charges: positve (+) charge and negative (-) charge. The unit of measurement of charge is the Coulomb (named after Charles A, Coulomb). In the context of electricity, the charge in motion that is of primary interest is the electron (negative charge, -e = -1.602 x 10^-19 C). In particular, the motion of valence electrons of metals called conductors. For example, copper (about 8.5 x 10²⁸ electrons per cubic meter are free to move) and silver are good conductors. In electronics, the concept of holes as positive charges in motion is also of interest. The motion of charge is current. The unit of measurement of current is the Ampere (named after Andre Marie Ampere) and its symbol is i. When the current is a function of time it is represented by i(t).
Technically, i = dq/dt (rate of change of charge with respect to time). In other words, 1 ampere is equal to 1 coulomb of charge moving through a fixed surface in 1 second. There are two types of current: direct current (DC) which flows in one direction; and alternating current (AC) which reverses polarity periodically.
(ii) Voltage is the electromotive force (emf) that moves charges from one point to another in an electric circuit. Voltage is also called potential difference. In other words, an electric energy with the capacity to do work under appropriate conditions. This energy is a consequence of the charge fields (electrostatic fields) of charges which exert attractive and repulsive forces. When one charge differs from another a potential difference is established between them. Electromotive force is the sum of potential differences in an electrostatic field. The unit of measeurement of voltage is the volt (named after Alessandro Volta). Consider points a and b in an electric field. If 1 joule of work is done in moving 1 coulomb of charge from a to b, then point b is at a potential difference of 1 volt with respect to a. In other words, the voltage or potential difference between two points in a circuit is the work done in moving charge from one point to the other.
(iii) Resistance is opposition to current flow. The material opposing the current is called a resistor. The unit of measurement of resistances is the ohm (named after Georg Simon Ohm). Ohm's Law relates voltage, current and resistance as follows:
voltage = current x resistance
(iv) Electric circuit is a current conducting network of connected electrical/electronic components that are being supplied by at least one voltage source. Any branch of an electric circuit is open (no current flows through it) if there is discontinuity in the contections of the branch (a branch is any portion of a circuit with two terminals connected to it). The branch is closed (current flows through it) if the connections are continuous. A short circuit implies zero resistance to current flow and therefore infinite current flow.

(b) Electric/electronic components of figure 7.7
- AC power supply: supplies primary voltage to the circuit
Conducting wire
- Fuse (F): monitors magnitude of current flowing. Effects an open circuit if current is above specification.
- Switch (S): on/off switch of the circuit.
- Step-down transformers (T1 and T2) : step down primary voltage to desired secondary voltage.
- Bridge (full wave) rectifier: changes AC to DC
- The following components work together to regulate stepped-down voltage:
- Capacitors (C1, C2, C3, C4). C1
- Resistors (R1, R2, R3, R4, R5, R6, R7, R8)
- Potentiometer (P1 and P2).
- Diodes (D1, D2, D3, D4, D5, D6).
- Bipolar Junction Transistors (Q1, Q2, Q3, Q4,Q5,Q6)
The capacitors, resistors, potentiometer, diodes and BJT transistors are doubled because the regulation circuit consists of two parts, the positive part (above circuit common) and the negative part (below circuit common. Both parts function in similar manner except for the difference in voltage polarity.

(c) Three stages of lab power supply circuit
- Primary voltage stepped down ---------> Rectification of AC ------------>Regulation of desired voltage.
Primary ac voltage: S₇P₃A₃₂ - (force-push)
AC is set in motion: S₇P₄A₄₁ - (motion-linears)
Transformers step down primary voltage to secondary voltage: S₇P₅A₅₁ - (change - physical)
Bridge rectifier changes AC to DC: S₇P₅A₅₁ - (change - physical)
Regulation of voltage stabilizes voltage: S₇P₇A₇₂ - (dynamic - equilibrium)

S₇P₁A₁₄S₇P₂A₂₁S₇P₆A₆₅S₇P₃A₃₂S₇P₄A₄₁S₇P₅A₅₁S₇P₇A₇₂