Bauhaus-Universität Weimar

Titel:
Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine
Person:
Gage, Henry Simon and Henry Phelps Gage
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit39438/542/
534 
RHEOSTATS AND OTHER BALLAST 
[Ch. XIII 
case there are two coils (fig. 291). If an alternating current supply 
is connected with the primary coil an alternating current can be 
drawn from the secondary coil. 
The voltage and amperage 
which can be drawn from the 
secondary coil will depend upon 
the electric supply and upon the 
relative number of turns of wire 
in the primary" and in the second¬ 
ary" coils. If the number of turns 
is the same in both, then the 
voltage and amperage remain 
practically the same as if the 
coils were not present. In other 
Fig. 290. Use of a Special Trans¬ 
former with an Arc Lamp. 
6' Dynamo. 
=*= Alternating current circuit. 
T Transformer. 
A Arc lamp. 
The primary of the transformer is 
connected to the dynamo while the 
secondary is connected to the arc words the circuit is in everv way 
lamr 
ip. 
The transformer has sufficient “re¬ 
actance" to serve as a ballast for the 
arc as well as to act as a step-down 
transformer. 
almost as if the wire were contin¬ 
uous. If the transformer were 
perfect the voltage and amperage 
would be exactly" the same as if it 
were not present. In practice they* are a little less, but a good 
transformer gives an efficiency" of 95% to 98%. 
If the secondary coil has a different number of turns from the 
primary coil then the voltage will vary directly as the ratio of the 
number of turns in the two coils, and the amperage will vary 
inversely" as that ratio. That is, assuming that there is no loss in 
the transformer, the watts delivered will remain constant as the 
product of volts x amperes remains the same. 
For example, suppose the secondary coil has J^ th as many turns 
as the primary" coil, then the number of volts across the secondary 
will be }4th the number across the primary" and the number of 
amperes delivered by" the secondary" will be four times the number 
drawn by" the primary". If now the primary" is connected to a 220 
volt line there will be a potential difference of one-fourth that 
number or 55 volts across the terminals of the secondary coil. 
Suppose the secondary" coil supplies 60 amperes, as might be the 
case with an arc lamp, then the primary" coil would draw one-fourth
        

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