Friday, May 30, 2008

Utilities (Building Systems) Principles of Electricity


Definition of Electricity:

Below are the most common meanings of the word Electricity. Which one do you think is right?

- "Electricity" means electric charge.

- "Electricity" refers to the flowing motion of electric charge.

- "Electricity" means electrical energy.

- "Electricity" refers to the amount of imbalance between quantities of electrons and protons.

- "Electricity" is a class of phenomena involving electric charges.

- Other less common definitions:
"Electricity" refers to the flowing motion of electric energy (electric power, Watts of electricity)
"Electricity" means electric field (Volts of electricity)
"Electricity" means the nitrogen/oxygen plasma (sparks of electricity)
"Electricity" is a field of science (Basic Electricity, Advanced Electricity)

If we wish to agree on a single correct definition of "electricity," below is the "clear" and "simple" description of electricity that results:

Electricity is a mysterious incomprehensible entity which is invisible and visible at the same time.
It is both matter and energy.
It's a type of low-frequency radio wave which is made of protons.
It is a mysterious force which looks like blue-white fire and yet cannot be seen.

When electricity flows through a light bulb's filament, it gets changed entirely into light.Yet no electricity is ever used up by the light bulb, and every bit of it flows out of the filament and back down the other wire. College textbooks are full of electricity, yet they have no electric charge.

Electricity is a class of phenomena which can be stored in batteries!

If you want to measure a quantity of electricity, what units should you use? Why Volts of course. And also Coulombs, Amperes, Watts, and Joules, ALL AT THE SAME TIME.

Yet "electricity" is a class of phenomena; it's a type of event. Since we can't have an AMOUNT of an event, we can't really measure the quantity of electricity at all, right?

So never ask "WHAT IS ELECTRICITY". Instead, discard the word "electricity" and use the correct names for all the separate phenomena.

Here are a few of them:
What is electric charge? What is electrical energy? What are electrons? What is electric current? What is an imbalance of charge? What is an electric field? What is voltage? What is electric power? What is a spark? What is electromagnetism? What is electrical science? What is electrodynamics? What is electrostatics? What are electrical phenomena?

These questions all have sensible answers. But if you ask WHAT IS ELECTRICITY?, then all answers you find will just confuse you, and you'll never stop asking that question.

Electricity. A form of energy produced by the flow of particles of matter and consists of commonly attractive positively (protons [+]) and negatively (electrons [-]) charged atomic particles. A stream of electrons, or an electric current.

Electricity \E`lec*tric"i*ty\, n.; pl. Electricities. [Cf. F. ['e]lectricit['e]. See {Electric}.]
1. A power in nature, a manifestation of energy, exhibiting itself when in disturbed equilibrium or in activity by a circuit movement, the fact of direction in which involves polarity, or opposition of properties in opposite directions; also, by attraction for many substances, by a law involving attraction between surfaces of unlike polarity, and repulsion between those of like; by exhibiting accumulated polar tension when the circuit is broken; and by producing heat, light, concussion, and often chemical changes when the circuit passes between the poles or through any imperfectly conducting substance or space. It is generally brought into action by any disturbance of molecular equilibrium, whether from a chemical, physical, or mechanical, cause.

Note: Electricity is manifested under following different forms:

(a) Statical electricity, called also Frictional or Common electricity, electricity in the condition of a stationary charge, in which the disturbance is produced by friction, as of glass, amber, etc., or by induction.

(b) Dynamical electricity, called also Voltaic electricity, electricity in motion, or as a current produced by chemical decomposition, as by means of a voltaic battery, or by mechanical action, as by dynamo-electric machines.

(c) Thermoelectricity, in which the disturbing cause is heat (attended possibly with some chemical action). It is developed by uniting two pieces of unlike metals in a bar, and then heating the bar unequally.

(d) Atmospheric electricity, any condition of electrical disturbance in the atmosphere or clouds, due to some or all of the above mentioned causes.

(e) Magnetic electricity, electricity developed by the action of magnets.

(f) Positive electricity, the electricity that appears at the positive pole or anode of a battery, or that is produced by friction of glass; -- called also vitreous electricity.

(g) Negative electricity, the electricity that appears at the negative pole or cathode, or is produced by the friction of resinous substance; -- called also resinous electricity.

(h) Organic electricity, that which is developed in organic structures, either animal or vegetable, the phrase animal electricity being much more common.

2. The science which unfolds the phenomena and laws of electricity; electrical science.

3. Fig.: Electrifying energy or characteristic.

electricity n1: a form of energy associated with moving electrons and protons 2: energy made available by the flow of electric charge through a conductor [syn: {electrical energy}] 3: keen and shared excitement; "the stage crackled with electricity whenever she was on it"

Basic Terminologies:

Atoms and Molecules
Matter is anything that has weight and thus takes up space
All matter is made up of molecules
All molecules are made up of atoms
The atoms is made up of protons and neutrons in a nucleus forming shells around the – much like the solar system
Electrons have a negative charge and protons have a positive charge
The electrons can be forced to move from one atom to the next and this is accomplished using an electromotive force (EMF)
This movement of electrons is electric current

Electric Current:
- When electricity flows it is measured in amperes (coulombs per second)
- One ampere of current is when one coulomb (6 million million million electrons) move past a point in one second. Thus electrical current is the rate of flow of electricity
- To make the electricity flow, an electromotive force is required.

Let's imagine that you have a wire, and you somehow observe that 2 coulombs passes through the wire in one second. What is the value of the current?

Ans. 2 amperes

You observe charge going through a wire for 4 seconds, and you find that 20 coulombs passes. What is the current?

Ans. 5 amperes

Now, if you reallly understand what current is you can turn this around. In the problems above you were given the charge passing through a wire in a given amount of time. Turning that around we can ask a different question. If we have a constant current, I, flowing through a wire, then we can compute how much charge flows through the wire in some given time interval.

Say we have the following situation:
I = Current = 3.2 amperes
Time interval = 15 seconds.
Then we would know that the amount of charge that flowed through the wire in the 15 second time interval would be:
Total charge = 3.2 amperes x 15 seconds
= (3.2 coul/sec) x 15 sec
= 48 couloumbs

The flow of electricity has two major forms – DC and AC
Direct Current (DC) is the one that flows in the same direction continuously, intermittently, or pulsating.
Alternating current (AC) is the one that reverses direction at regular intervals

Electromotive Force
- Electromotive force is measured in volts
- EMF can be generated using batteries that operate from chemical reactions
- EMF can be generated by moving a conductor in a magnetic field (generators)
- EMF can be generated by rubbing two dissimilar materials together (car seats and you)
- EMF can be generated using many other means including light and pressure to crystals.

Resistance is the opposition to the flow of electricity.
All known matter resist the flow of electricity.
The movement of electricity through a resistor causes some of the electrical energy to be converted to heat energy.
The unit of resistance is the OHM.

Electric Circuit:

A circuit is the path electricity takes as it flows from a battery through an object and back to the battery. One end of the connecting wire must touch the positive terminal (+) of a battery (or cell); the other end must touch the negative terminal (-) of a battery.

An Electric circuit is made from a power supply, wires and electrical devices. They must be connected without a break for electric current to flow around the circuit.
Switches control where the current flows. Circuit diagrams show how the parts of the circuit are connected. The parts of the circuit can be connected in different ways.


Ampacity. "The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating." (Ampacity varies depending on many factors. You must use the appropriate NEC Tables to determine the correct ampacity.)

Relation between EMF, Current and Resistance (Ohm’s Law)

Ohm’s Law
By international standards, one volt is the amount of EMF required to move one ampere of current through a resistance of one ohm. Ohm’s Law is:
E = I x R I = E/R R = E/I

Given a circuit has a current of 4 amperes and a resistance of 10 ohms. What is the voltage?
E = I x R E(volts) = 4 amperes x 10 ohms = 40 volts

Given E = 120 volts, and resistance = 60 ohms, what is the current?
I = E/R = 120volts/60ohms = 2 amperes

Electric Circuits/Electric Currents
Discuss and review the vocabulary you will be using
dry cell


Electric current is the flow of electric charge from high potential to low potential. Therefore we say that current is caused by a potential difference. An electric circuit is a closed path through which charge can move (conductor).

When one coulomb of charge passes a given point every second, we say that a current of 1 Ampere (Amp or A) exists in the circuit.

How can the birds sit on the power lines without getting fried?
Why do electricians say, "It's not the volts, it's the amps that can hurt you."?

#1 - The birds can sit on the power lines because there is very little potential difference between their feet and therefore very little current will go through them.
#2 Amps are the actual moving of charges, which can cause damage to you as well as interfere with the electrical activity in your body. Volts (potential difference) are what would cause the current to go through you. Volts do not travel through anything and therefore cannot hurt you. The only reason volts are dangerous is the amps they can generate! ResistanceA high voltage (potential difference) does not necessarily lead to a high current, it depends on the resistance of the material that the current has to go through.

The resistance of a wire depends on three things: what it is made out of (resistivity), the cross-sectional area of the wire, and the length of the wire.

The resistance can be calculated as follows: r = ρL/A where the ρ resistivity is found using the reference tables.

What is the resistance of 1.0 meters of Nichrome wire (diameter = 0.04318 cm)?

First we have to find the cross-sectional area (in m2) of the wire.
Assuming the wire is round the cross-sectional area is that of a circle, which is: A= πr2 = π (.0002159m) 2 and resistance is =10.2Ω

Electric Power and Energy:

Power is the rate that energy is transferred.
Power is measured in watts which are joules per second.
P=VI watts = volts x amperes

To calculate the energy (in joules) which is dissipated (lost) in a resistor during a certain period of time just multiply the power in watts times the time in seconds.

Another unit of energy is the kilowatt hour (kWhr). This is found by multiplying the power in kilowatts (1000 watts) times the time in hours.

Joules. The modern definition of the calorie is based one the meter-Kg-sec units and is defined as 4.184 joules. The joule is the unit of energy in meter-Kg-sec units.

Electric Circuits:
Electric circuits are complete paths including resistors made between the positive and negative terminals of a battery.
Multiple resistors can either be connected to make one path, called a series circuit or multiple paths, called a parallel circuit.

Kirchhoff's Current Law (KCL).
KCL states that the algebraic sum of the currents in all the branches which converge in a common node is equal to zero

sum(Iin )=sum(Iout )

Kirchhoff's Voltage Law.
Kirchhoff's Voltage Law states that the algebraic sum of the voltages between successive nodes in a closed path in the network is equal to zero.

Sum(E) = sum(IR)

KIRCHHOFF'S RULES. The following two rules are known as Kirchhoff's laws.
1. Junction or Point rule: Sum of all currents entering a junction must equal sum of currents leaving the junction.
2. Loop or Circuit rule: For a closed loop in a circuit, the algebraic sum of all potential changes encountered while completing a cycle around the loop must be zero. In this Loop rule, we may consider a rise in the potential to be positive and a drop in the potential to be negative.

1 comment:

  1. wow... a big help!!!
    2nd year CAFA Student po ako ng PUP! tamang-tama to sa Utilities 2 subject namen...

    I guess I'll be dropping by here more often than I thought!

    have a nice day poh!!!