Art of Electronics 2nd edition, pages 2-4

**Overview**

Voltage & Current describe two aspects of electronic circuits that are fundamental to understand and on which everything else will build on.

**What you MUST learn**

Voltage refers to a force that when applied across a circuit causes current to flow. Voltage is measured in volts (using the symbol V) also called a “potential difference”. It is measured across two points in a circuit. A joule of work is needed to move a coulomb of charge through a potential difference of one volt. A coulomb is the charge of about 6×10^18 electrons.

Current (symbol: I) is the measure of electronics through a point in a circuit. It is measured in amperes (amps) (symbol: A). 1 ampere (amp) is 1 coulomb of charge passing through a point per second.

Conservation of Charge: Kirchhoff’s current law

The sum of currents into a point or node is equal to the sum of the currents out of a point or node. This is referred to as Kirchhoff’s current law.

Kirchhoff’s voltage law

The sum of voltage drops through one branch of a circuit will equal the sum of voltage drops across the other branches of the circuit.

P=VI

Power (work per unit time), measured in watts. (1 W = 1 J/s)

P=VI = (work/charge) x (charge/time) = work/time

P=VI= (1 joules/1 coulomb) x (1 coulomb/1 second) = 1 joules/second = watt.

**Things good to learn**

Voltage is usually written with the symbol V but sometimes E is used. Voltage is also called a “potential difference” or electromotive force (EMF).

Prefixes:

Multiple | 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 |

When abbreviating a unit with a prefix, the unit follows the multiplier with no space and the unit is capitalized. However, no capitalization for both prefix and unit when spelled out. 1mW = 1 milliwatt

1 MV = 1 megavolt

**Related information and insights from my other books**

Introductory Circuit Analysis 9th edition – chapter 2

Structure of the atom:

nucleus is made up of protons (that have a positive charge) and neutrons that have a negative charge. The proton and neutron are relatively the same mass. But the electron is considerably smaller (1836 times smaller) than the proton but has a negative charge that is equal to the positive charge of the proton.

**Other things of interest**

**If you need more help**

Voltage

Current

Joule

**If you wanted to know**

Who defined:

Voltage

Volt

Current

amp

joule

watt

multiplier prefixes

People who contributed:

Watt

Power Point:

GadgetNateJourneyThroughArtOfElectronics-01.01-VoltageAndCurrent