Monday, December 3, 2012

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
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