Introduction Dr. Farid Farahmand CET 323

Introduction Electricity is everywhere! But what is it? –Movement of electrons through a conductor metal –Electrons move all over the place in a conductor –They glide through like marbles sliding on the floor Less resistance  More moving The electrons can move but something must more them The force that pulls electrons from one place to another is called voltage

Electrical Energy Electrical Energy can be generated from other forms of energies Coal, oil, natural gas –Creates steam to drive a turbine that generates electricity. Nuclear or solar energy –Creates the steam to drive the turbine. Solar photovoltaics or fuel cells and batteries –Rely upon chemical reactions to generate electricity

Movement of Electrons Early experiments appeared as if flow of electrons is from + voltage to – voltage But in reality, flow of electrons is from - voltage to + voltage When electrons move from negative to positive terminals, the flow is called an electric current Voltage is the driving force in electric circuits and is what establishes current

Current Flow Current flow can be Direct or Alternating –Direct of DC: Electric flow is only in one direction –Alternating or AC: Electric flow is in one direction and then in another Property of material that resists the flow of electrons is called resistance

Units Voltage V is represented by Volt (V) Current is I represented by Amp (A) Resistance R is represented by Ohm (  ) It turns out that V = IR

Electric Shock! Remember V = IR; I = V/R Humans are conductors of electricity and have electrical resistance similar to any other material. –The human body's resistance to current flow varies depending on the internal and external moisture — exposed sub-epidermal tissue and skin thickness. So, what is electric shock? –Current flow through body  Pain! –Human resistance is about 10,000 ohms on the high side and as little as 1,000 ohms if the person is wet –If 10 Volt is applied to human body, it results in a current flow of about 1-10 mA: That hurts! –The longer the path of the electricity through the body  More damage!

Electrical Components By controlling the flow of electrons and the energy potential between two points we do wonders! Resistors: Resist or limit electrical current flow in a circuit –Axial leads, Network of resistors, Power resistors, Variable resistors Capacitors: Store electric charges; block DC current and pass AC –Electrolytic (Have polarity) –Ceramic (No polarity) –Variable

Electrical Components Inductors: Coils storing energy in an electromagnetic field Transformers: Coupling or changing the magnitude of AC voltage Semiconductor Devices –Diodes –Transistor –Integrated circuits

International System (SI) Units We use many different measurable quantities –Different components have different units To represent these quantities, we use SI units –Electrical SI units: Capacitance, resistance, frequency, resistance –Magnetic SI units: Density, tesla, etc.

Engineering and Scientific Notations SI units can have very small or large quantities –We typically use scientific notations – representing number in power of 10 –Examples: 2x10 -2, 5.4x10 +3, , x10 +6 –Engineering notations uses 10 +/-3, 10 +/-6, 10 +/-9, 10 +/-12, 10 +/-15, etc.

Scientific Notations To express a large number as a power of 10, move the decimal point to the left and count the number of places the decimal point is moved. The number of places counted indicates the power of 10. As an example let’s convert 81,337 to scientific notation. We would start out by changing the number to Count the number of places the decimal moved to the left. Since it moved to the left 4 places, the number becomes X Here are a few other examples: 320,000 becomes 3.2 X ,050,000 becomes X 10 8 To express a decimal fraction in scientific notation, express the fraction as a whole number times a power of 10. Move the decimal to the right and count the number of places it has been moved. The number of places moved will be the negative power of 10. Consider the number First change the number to 3.2. Count the number of places the decimal moved to the right. We moved the decimal 2 places, thus the number is 3.2 X Here are some other examples: becomes 4.5 X becomes 3.06 X 10 -5

The prefixes associated with engineering notation

Using Engineering Notations For the number 6,250,000,000,000,000,000 we would move our decimal point to the left 18 positions. Our number would become 6.25 X That’s right! A coulomb represents the quantity of electrical charge carried by 6.25 X electrons. It’s been said that if electrons were house flies, a "coulomb" of dead flies would cover the state of New York to a depth of several feet! To convert , we would move our decimal point to the right 6 positions. Our number would then become 3 X According to our list, this number would have a "Micro" prefix. Thus our radio would break squelch at 3 microvolts or, using the symbol, 3 m volts. What about the number 3.06 X ? This number is expressed in scientific notation not engineering notation. If you told some one that you wanted to measure 3.06 X amperes you would probably get a strange look at the very least. This answer is impractical and inappropriate. If we move the decimal place to the right one position, the exponent will decrease by one (remember -6 is less than -5). Our number becomes 30.6 X or 30.6 microamps. A technician would have no trouble determining what scale to use to measure this quantity.

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