AEG Electrolux ERN 2922 User Manual download pdf (Page 49)

Mathematical

Variations

of Ohm's

Law

By C.R.

Ball Jr.

German

physicist

Georg

Si-

mon Ohm

discovered

the

relationship

between

volt-

age,

current

and

resistance,

circa

1854. In

honor of

his discovery,

the

relationship

became

known

as

Ohm's

Law,

and the "Ohm,"

abbre-

viated

as

S2 (the

Greek

letter omega),

ultimately

became

the officially

rec-

ognized

MKS unit

of resistance.

Several

mathematical

variations

and definitions

of Ohm's

Law exist.

These

are

mathematically

summar-

ized

in the Ohm's

Wheel

shown

here.

With

this Wheel,

you

can start

at

the

hub and derive

any

variation of

the

TABLE

1

MATHMATICAL

VARIATIONS

OF OHM'S

LAW

Ohm's

Wheel

WHERE

E =

Potential

Difference

in Volts

I

=

Current

in Amperes

R =

Resistance in

Ohms

W = Power in Watts

Law by going

to the

appropriate

quadrant.

Traditionally,

electromo-

tive

force, or

voltage is

represented

by an

"E," current

by

an "I" and

re-

sistance

by

an "R."

To these

three

basic

parameters

have been

added

power

in

watts, represented

by a

"W

In essence,

Ohm

postulated

that

when

a potential

of

1

volt is placed

across a

1 -ohm

resistance,

the cur-

rent flowing

through

the

resistance

would

be

1 ampere.

To use Ohm's

Wheel to calculate

any given

parameter,

you

start

at the

hub and

use the

appropriate

formula

of the

three shown

in that specific

quadrant.

For example,

if you

know

the

voltage

applied

to a

known

value

of resistance,

you

would

start

at the

hub

of

the unknown

current

(lower

-

left)

quadrant

and discover

that

volt-

age (E)

divided by

resistance

(R)

will

provide the

unknown

current.

If the

potential

is

10

volts

and

the current

is

1 ampere, you

would solve

the prob-

lem

as

follows:

I =

E/R

I = 10

volts/

1 ampere

I = 10 ohms

Now you

can

go a step

further

and

calculate

the

power

dissipated

by the

resistor. The easiest

way to do

this

is

to use

any of

the

formulas

in the

power

quadrant

(lower-

right)

of the

Wheel.

In the

simplest

of these

for-

mulas, you

just

multiply

voltage by

current:

W = I

x E

W =

1 ampere

x 10

volts

W = 10

watts.

That's all there

is to

it!

Newcomers

to

electronics,

and

even old

hands,

will

want

to

keep this

Ohm's Wheel

handy

as a

reference.

AE

Say

You Saw

It In Modern

Electronics

NEW

FROM

EEB

NOW buy

that

test

equipment

you've

wanted

and save!

DIPMETER

1.5

To 250

MH:

AM

Modulation

6

Plug -In

Coils

Xtal

-osc

1 -15

MHz

9V

battery _

DM4061

\ ` $109.95

Vah,

.

I

ONLY

57995

«$4

UPS

Measure

resonance

of antennas

and

tank circuits.

Check

for

Harmonic

radiation.

Use

as OSC

for

Rec. alignment.

More uses detailed

in the

RSGB

Hand-

book.

pages

18.15 to

18.21.

RF SIGNAL

SG4160

GENERATOR

100 KHz -150

MHz to

450

MHz

on

harmonics.

RF Output

100 mVs.

Modulation:

Int. -

1 KHz

Ext.

-

50

Hz to 20

KHz.

Crystal OSC

1 - 15 MHz.

ONLY

514995 + $4

UPS

" .-

a "' ' ' -

S219.95

Value

PM330

RF

POWER

METER

/LOAD

1

8

to 500

MHz.

500HM

-N -J

Connector.

5W, 20W,

120 Watts.

Accurate to

+/-

10 %.

ONLY

57995+

$4

UPS

5109.95 Value

FREQUENCY

FC5250

COUNTER

10 Hz

to

150 MHz

7

Digit

readout.

Gate

1s 8 6 sec.

Accurate to

+/-

1

count.

25

-

100 mV to

30

MHz

100

- 300

mV

to

150 MHz

ONLY

$12995 +

$4

UPS

included

with

unit.

l

SENSITIVITY:

$169.95

Value

AC

Adapter is

RF ATTENUATOR

DC -500

MHz

RFA8000

0 - 81

dB

in

1

dB steps.

Accurate

to

+/-

.3 dB

Steps

1.

2. 3, 5,

10

and

20 dB

50 OHm

- v?

Watt

Insertion

Loss .5 dB.

S299.00

Value

ONLY

514995 +

$4

UPS

SWR

/RF

ANTENNA

METER

SWR3P

Read SWR,

RF

power and

field

strength.

17 150

MHz.

10 or

100

watt range.

SWR

+/- 5 %:

POWER

+1 -10 %accuracy

$29.95

Value ONLY

51995 +

$4

UPS

Prices and

Specs

Subject

to

Change

Equipment

Bank

Mill Street,

N.E.

Virginia

22180

orders.

technical

questions

703

-938

-3350

CHOICE.

and DISCOVER

-368

-3270

-

33:

Electronic

516

Vienna,

Virginia

VISA.

MASTERCARD

800

CIR(

I 1 12

UN

F

REF. INFORMA

HON

CARI)

February

1988

/ MODERN

ELECTRONICS

/ 61

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 79 80

Comments to this Manuals

No comments