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     If we know any two of these, it will be a simple matter to find the third or the unknown term. Suppose we have a street light circuit. We know that the voltage is 110. The street lamp has a resistance of 18 ohms (the unit of resistance is the ohm, named after Dr. Ohm). We want to find the amount of current flowing. According to our equation, I=E ÷ R, substituting numbers for the known terms we get I = 110 ÷ 18 = 6.3 amperes--and the unknown is known.
     You will find occasion to use this simple equation all through your studies, and in your practical work as well. In a very near lesson we shall study this equation thoroughly and

TABLE NO. 10

A.C.	Alternating Current	kv.	Kilovolt
AF	Audio frequency	kw	Kilowatt
B & S	Brown & Sharp Wire Gauge	M	Mutual inductance
C	Capacity	ma	Milliampere
cm	Centimeter	mfd	Microfarad (µf)
CW	Continuos Wave	mmfd	Micro-microfarad (µµf)
db	Decibel	PD	Potential difference
DC	Direct Current	Q	Quantity
DCC	Double cotton covered wire	R	Resistance
DSC	Double silk covered wire	RF	Radio Frequency
E	E. M. F.	SCC	Single cotton covered wire
emf	Electromotive force	SSC	Single silk covered wire
f	Frequency	T	Time
h	Henry	TU	Transmission unit
I	Intensity (current)	V	Voltage
ICW	Interrupted continuous waves	VT	Vacuum tube
kc	Kilocycle	wh	Watt hour

learn all its applications to Radio. Watch how often you will use it when you get to repairing sets. You will have many chances to use the "tools" you are becoming familiar with in this lesson.

FORMULAS      Equations that have been proved to hold true under all conditions are called formulas to distinguish them from ordinary equations which apply only to certain conditions. The equation which we developed p - s ÷ 4 applies only to the particular Radio dealer we had in mind. If we developed equations from

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Content	©1931, National Radio Institute
Webpage	©1997, Nostalgia Air
Transcriber	Richard Lancaster