Electronics

Kirchhoff's Rules

Current Rule or Junction Rule (conservation of charge)

 

The algebraic sum of the currents entering any junction must equal the sum of the currents leaving that junction.

Therefore, in a series circuit the current is the same everywhere.

 

Voltage Rule or Loop Rule (conservation of energy)

 

The algebraic sum of the potential differences (voltage drops) around a closed conducting loop must equal zero.

Therefore, components connected in parallel have the same voltage across them.

Ohm's Law

where voltage V is in volts, resistance R is in ohms and current I is in amperes.

Joule's Law

where power P is in Watts, voltage V is in volts, resistance R is in ohms and current I is in amperes.

Thévenin's Theorem

Any two-terminal network of resistors and voltage sources is equivalent to a single resistor in series with a single voltage source.

Definitions

1 ampere = 1 coulomb/second

1 coulomb = 1 ampere · second

1 farad = 1 coulomb/volt

1 joule = 1 newton · meter

1 newton = 1 kg · meter/second²

1 ohm = 1 volt/ampere

1 volt = 1 joule/coulomb

1 Watt = 1 joule/second

Symbols, Dimensions and Units of Physical Quantities

Quantity	Common Symbol	Unit	Unit Symbol
Capacitance	C	farad	F
Charge, electrical	q, Q, e	coulomb	C
Current	I	ampere	A
Energy	E, U	joule	J
Force	F	newton	N
Frequency	f, v	hertz	Hz
Length	l, L	meter	m
Potential, electrical or Voltage	V	volt	V
Power	P	Watt	W
Resistance	R	ohm
Time	t	second	s
Work	W	joule	J

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