V = Volts
R = Resistance (ohms, )
I = Current ( Amps)

Formular

Example

V
= R * I

5
* 2A = 10Vs

I
= V / R

10V
/ 5
= 2A

R
= V / I

10V
/ 2A = 5

Watts

W
= Watts
V = Volts
I = Current ( Amps)

Formular

Example

W
= V * I

10V
* 2A = 20W

I
= W / V

20W
/ 10V = 2A

V
= W / I

20W
/ 2A = 10V

W
= R * I2

5
* 2^{2} = 20W

W
= V2 / R

10V^{2}
/ 5
= 20W

R
= W / I2

20W
/ 2A^{2} = 5

R
= V2 / W

10V^{2}
/ 20W = 5

AC Theory

RMS

0.707
Peak voltage

Impedance

AC current in a capacitive or inductive component.
Impedance is the resistance ( measured in ohms ) of a reactive component
( capacitor, inductor ) at a certain AC frequency.

Capacitor

Inductor

Xc
= 1 / ( 2 * Pi * f * C )

Xl
= 2 * Pi * f * L

where

Pi
= 3.14

where

Pi
= 3/14

f
= frequency in Hz

f
= frequency in Hz

C
= capacitance in Farads

L
= Inductance in Henry

eg

A
100uF cap at 50Hz

eg

A
20mH inductor at 50Hz

Xc
= 1/(2*3.15*50Hx*0.0001F)

Xl=2*3.14*50Hx*0.02

Xc
= 31.8 ohms

Xl
= 6.28 ohms

Multipliers.

Pica

0.000,000,000,001

1^-12

Nano

0.000,000,001

1^-9

Micro

0.000,001

1^-6

Milli

0.001

1^-3

Centi

0.01

1^-2

Unit

1

1

Kilo

1,000

1^3

Mega

1,000,000

1^6

Giga

1,000,000,000

1^9

Tera

1,000,000,000,000

1^12

The Metric system.

All measurements are based on a unit, and a multiplier,
like those above. ie for distance we use a measure called the meter,
and thats the only unit of distance we need to remember. We also
use a multiplier, so we call 1000 meters a KiloMeter, or 1/1000
of a meter is a MilliMeter. Easy.

Another easy one to remember is Centigrade as a
measurement of temperature. Water freezes at 0 degrees, and boils
at 100 degrees. Body temperature is about 32 degrees C.