1 ELECTRICAL TECHNOLOGY EET 103/4 Define and explain the meaning of current, voltage, resistance, power, conductor, and insulator

2 Electric charge (Q) Nucleus –Protons –Electrons –Neutrons Atoms and their structure The orbiting electron carries a negative charge equal in magnitude to the positive charge of the proton.

3 Electric charge (Q) The atomic structure of any stable atom has an equal number of electrons and protons.

4 Electric charge (Q)

5 Ions are imbalance atoms (+ve or –ve) Electric charge (Q)

6 Opposite charges attract; same charges repel Unit for electric charge is coulomb (C). 1 coulomb (C) is equal to the total charge of x electrons. Electric charge (Q)

7 Coulomb is not normally used because it is too big a unit. The common units are millicoulomb (mC) and microcoulomb (  C): Electric charge (Q) 1 mC = C 1  C = C

8 Voltage (V) The flow of charge is established by an external “pressure” derived from the energy that a mass has by virtue of its position: Potential energy Energy: the capacity to do work – If a mass (m) is raised to some height (h) above a reference plane, it has a measure of potential energy expressed in joules (J) that is determined by –W (potential energy) = mgh where g is the gravitational acceleration (9.8 m/s 2 )

9 Voltage (V) The unit of measurement is volt (V) A potential difference of 1 volt (V) exists between two points if 1 joule (J) of energy is exchanged in moving 1 coulomb (C) of charge between the two points

10 Voltage (V) For large values of voltage, kilovolt (kV) and megavolt (MV) are used: 1 kV = 10 3 V 1 MV = 10 6 V For low values of voltage, millivolt (mV) and microvolt (  V) are used: 1 mV = V 1  V = V

11 Voltage (V)

12 A potential difference or voltage is always measured between two points in the system. Changing either point may change the potential difference between the two points under investigation. Potential difference between two points is determined by: V = W/Q (volts) Voltage (V)

13 Notations for sources of voltage and loss of potential – E - Voltage sources (volts) – V - Voltage drops (volts) Potential – The voltage at a point with respect to another point in the electrical system. Typically the reference point is the ground, which is at zero potential. Voltage (V)

14 Potential difference: The algebraic difference in potential (or voltage) between two points of a network. Voltage: When isolated, like potential, the voltage at a point with respect to some reference such as ground. Voltage (V)

15 Voltage difference: The algebraic difference in voltage (or potential) between two points of a system. A voltage drop or rise is as the terminology would suggest. Electromotive force (emf): The force that establishes the flow of charge (or current) in a system due to the application of a difference in potential. Voltage (V)

16 Voltage Sources DC voltage source

17 Voltage Sources DC voltage source

18 Voltage Sources DC voltage source

19 Voltage Sources DC generator

20 Voltage Sources Symbol OR

21 Current (I) The free electron is the charge carrier in a copper wire or any other solid conductor of electricity With no external forces applied, the net flow of charge in a conductor in any one direction is zero

22 Motion of negatively charged electrons in a copper wire when placed across battery terminals with a difference in potential of volts (V). Current (I)

23 Basic electric circuit Current (I)

24 Unit for electric current is ampere (A). 1 ampere (A) = 1 coulomb (C) per second (s) Current (I)

25 Current (I) 1 kiloampere (kA) = 10 3 A 1 milliampere (mA) = A 1 microampere (  A) = A

26 Safety considerations – Even small levels of current through the human body can cause serious, dangerous side effects – Any current over 10 mA is considered dangerous –currents of 50 mA can cause severe shock –currents over 100 mA can be fatal – Treat electricity with respect – not fear Current (I)

27 Current Source An ideal current source supplies a constant current to any load irrespective of the value of the load. Symbol

28 Conductors and Insulators Conductors are those materials that permit a generous flow of electrons with very little external force (voltage) applied In addition, Good conductors typically have only one electron in the valance (most distant from the nucleus) ring.

29 Insulators are those materials that have very few free electrons and require a large applied potential (voltage) to establish a measurable current level Insulators are commonly used as covering for current-carrying wire, which, if uninsulated, could cause dangerous side effects Conductors and Insulators

30 Conductors and Insulators Rubber gloves and rubber mats are used to help insulated workers when working on power lines Even the best insulator will break down if a sufficiently large potential is applied across it

31 Conductors and Insulators

32 Conductors and Insulators Table 2.1 shows the relative conductivity of various materials

33 Table 2.2 shows breakdown strength of some common insulators Conductors and Insulators