1.01 Voltage and Current

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Fundamentals

• charge – coulomb (charge of about 6x10^18 electrons)• current – amperes, amp, A (coulomb/second)• newton - (equivalent to accelerating 1 kg by 1 meter/second^2)• energy – joule (1 newton through 1 meter)• voltage – volts, V (1 joule of work is needed to move a coulomb of charge through 1 volt)• power – watt, W (1 joules per second: 1W = 1J/s)

Introductory Circuit Analysis 9thEdition – chapter 2 (voltage and current)Getting Started in Electronics (Forrest M. Mims, III) – chapter 1Physics for Scientists and Engineers 3rd edition – chapter 25Wikipedia: http://en.wikipedia.org/wiki/Joule http://en.wikipedia.org/wiki/Newton_(unit)

Voltage, Current, Power

Voltage (V): electrical force between two points or across two points. Also seen as the force between a point and a common reference called “ground”; measured in volts (V); 1 joule is required to move 1 coulomb of charge through 1 volt

Current (I): 1 coulomb passing through a point in a second. Measured in amperes (amps) (A).

Power (P): measured in watts. P=VI

Kirchhoff’s current and voltage laws

• Kirchhoff’s current law (conservation of charge). The sum of the currents into a point is equal to the sum of the currents out of the point.

• Kirchhoff’s voltage law – the voltage between two nodes is the same across every branch connecting those two nodes

prefixesMultiple Prefix Symbol

10^12 tera T

10^9 giga G

10^6 mega M

10^3 kilo k

10^(-3) milli m

10^(-6) micro µ

10^(-9) nano n

10^(-12) pico p

10^(-15) femto f

Property Unit Symbolvoltage (V) volt Vcurrent (I) amp Apower (P) watt W

When using the prefix with the unit or using symbols there are no spaces. Also, spelled out it is in all lower case, but when using the symbol for the unit, a capital letter is used.

Examples:

10 kiloamps = 10 kA12 millivolts = 12 mV8 picowatts = 8 pW