CHAPTER 12 USEFUL FORMULAE

D.C. CIRCUITS AND OHM’S LAW

                                                                                   

Ohm’s Law:	V	=	IR
or	I	=	V
			R
or	R	=	V
			I
Heating Rate:		=	I2R watts (W)

                                                                                   

INDUCTANCE

Back-emf       E	=	-L	di
			dt

Stored Energy:	=	½LI2 joules (J)

Time Constant	=	L	seconds
		R

CAPACITANCE

Stored Energy:	=	½CV2 joules (J)
Time Constant	=	CR	seconds

Capacitances in series	1	=	1	+	1	+	1	+	….
	C		C1		C2		C3

Capacitances in parallel

C

=

C1

+

C2

+

C3

+

….

RESISTANCES IN SERIES AND PARALLEL

Resistances in series	R	=	R1	+	R2	+	R3	+	….
Resistances in parallel	1	=	1	+	1	+	1	+	….
	R		R1		R2		R3

 

D.C. POWER

                                                         Power:         VI     watts

or	I2R	watts
or	V2	watts
	R