Values Units Ing Jaroslav Bernkopf Values Units Objectives

Values & Units Ing. Jaroslav Bernkopf

Values & Units Objectives • Symbols, units • Frequency – period • Types of current & voltage http: //skola. bernkopf. cz jaroslav@bernkopf. cz 2

Values & Units Vocabulary English abbreviation AC = Alternating Current again between bit bps byte capacitance capacity capital charge current DC = Direct Current efficiency event flow, flew, flown frequency happen in case of inductance information instead of letter maintain Czech http: //skola. bernkopf. cz English memory name after number occurrence often per second periodically polarity power factor propose pulsating quantity reciprocal resistance reverse successive sum the same unidirectional unit value jaroslav@bernkopf. cz Czech 3

Values & Units Symbols & Units Quantity Voltage Current Resistance Capacitance Inductance Power Frequency Period Memory capacity Qty of information Symbol Unit Abbreviation V volt V I ampere A R ohm Ω C farad F L henry H P watt W f herz Hz T second s http: //skola. bernkopf. cz bit, byte jaroslav@bernkopf. cz b, B 4

Values & Units Frequency & Period For base units, capital letters are normally used when the unit was proposed and defined by an individual after whom the unit is named. Take, for example, the bel (a unit that measures the intensity of sound). Abbreviated, the bel is "B", because it was named after Alexander Graham Bell. Others include the hertz ("Hz", Heinrich Hertz), the newton ("N", Sir Isaac Newton), and the watt ("W", James Watt). http: //www. writersblock. ca/tips/monthtip/tipnov 97. htm http: //skola. bernkopf. cz jaroslav@bernkopf. cz 5

Values & Units Frequency & Period Frequency is the number of periods per second. Frequency tells how often something happens. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 6

Values & Units Frequency & Period The unit of frequency is the Hertz (symbol Hz). http: //skola. bernkopf. cz jaroslav@bernkopf. cz 7

Values & Units Frequency & Period A period is the time between two successive occurrences of the same event. Period tells the time that something takes to happen again. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 8

Values & Units Frequency & Period The unit of period is the second (symbol s). http: //skola. bernkopf. cz jaroslav@bernkopf. cz 9

Values & Units Frequency & Period Frequency is equal to the reciprocal of the period. Frequency is equal to one over the period. Period is equal to the reciprocal of the frequency. Period is equal to one over the frequency. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 10

Values & Units Types of voltage and current A direct current is unidirectional flow of electric charge. A direct voltage has the same polarity at all times. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 11

Values & Units Types of voltage and current A pulsating current is a unidirectional current that changes in value. A pulsating voltage is a sum of a direct voltage and an alternating voltage. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 12

Values & Units Types of voltage and current Alternating voltage reverses its polarity periodically. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 13

Values & Units Types of voltage and current Physical Science 6. 3 b - DC and AC http: //www. youtube. com/watch? v=AI_6 lb. XA-HE http: //skola. bernkopf. cz jaroslav@bernkopf. cz 14

Values & Units Types of voltage and current Why do we use Alternating Current in our homes ? Why not Direct Current? I've heard that in case of AC Power = Voltage * Current * Power Factor and for good efficiency the Power Factor should be maintained properly. and In case of dc Power = Voltage * Current There is no Power Factor. Then if there is no problem of maintaining power factor in dc then why don't we use DC instead of AC? http: //skola. bernkopf. cz jaroslav@bernkopf. cz 15

Values & Units Types of voltage and current Best Answer - Chosen by Voters There are two separate issues involved in this question that people have been asking for well over one hundred years. [1] Which is better for transporting electrical energy from the power station to the consumer's house, AC or DC? [2] Which is better for powering appliances in the consumer's house, AC or DC? There is no doubt that AC is better than DC for long distance transportation because it is easy to produce the high voltages that make it economical to transport energy over long distances. Once the supply reaches the consumer's house or factory, it would be useful to have it "divide" into AC and DC as both types of supply would be useful BUT this would be extremely complicated as a wide range of voltages would be needed. Houses would not benefit greatly from having a DC supply. In a factory, many machines would be best designed to run on DC but AC versions are perfectly satisfactory. Where large electric motors are concerned, AC is essential. I have installed 500 Horsepower AC motors in circumstances in which I would never have considered DC motors. Low power factor is an inherent part of an AC system. If the electricity fairies banished low power factor, they would have to do so by banishing induction and by banishing induction, they would make it impossible to run a transformer or motor. In short, both AC and DC supplies would be useful but it is more economical to use an AC supply and then use converters to produce DC for special purposes. Were you building a house 300 miles from the nearest power line, you could use photovoltaic arrays to charge a large bank of batteries that would then supply DC appliances. This would make efficient use of the energy stored in the batteries but you would have to have a lot of the appliances custom made for you. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 16

Values & Units Types of voltage and current 1. Why do we use Alternating Current in our homes? Why not Direct Current? 2. What is frequency? 3. Describe a pulsating current. 4. What does the following sentence mean? „It reverses its polarity periodically. “ 5. What is the unit of frequency? http: //skola. bernkopf. cz jaroslav@bernkopf. cz 17

Values & Units Q&A Thank you. Questions? http: //skola. bernkopf. cz jaroslav@bernkopf. cz 18

Values & Units Container Napětí, proud, výkon Střídavý, stejnosměrný, pulzující Kmitočet, perioda, periodický Kapacita paměti, bit, byte, kb, k. B, . . resistance is equal to - odpor je roven resistance is zero – odpor je nulový The input voltage is positive. - Vstupní napětí je kladné. The output voltage is positive, too. - Výstupní napětí je také kladné. http: //skola. bernkopf. cz jaroslav@bernkopf. cz 19