. Elementary and dental radiography . induction coil is, however, practically auni-directional one, while the current supplied by the high-frequency coilis alternating at the inconceivably high frequency of tens of thousandsor millions. Hence the term high frequency, which is applied to thecurrent and the coil producing it. The frequency is governed by the size of the condenser; the smallerthe condenser the higher the frequency. Thus most high-frequency andX-ray machines are equipped with a switch, by means of which all, or X-RAY MACHINES 35 a part, of the condenser may be used. When using the
. Elementary and dental radiography . induction coil is, however, practically auni-directional one, while the current supplied by the high-frequency coilis alternating at the inconceivably high frequency of tens of thousandsor millions. Hence the term high frequency, which is applied to thecurrent and the coil producing it. The frequency is governed by the size of the condenser; the smallerthe condenser the higher the frequency. Thus most high-frequency andX-ray machines are equipped with a switch, by means of which all, or X-RAY MACHINES 35 a part, of the condenser may be used. When using the coil for X-raywork, this switch should be turned to low frequency, so that all of thecondenser is used. When using the coil for high-frequency treatments—using the current as a therapeutic agent—the switch should be on highfrequency, so that only a part of the condenser is used. By means of the regulating spark gap, we can control to an extentthe secondary current of the second coil—the current supplied by the -•^ *Sp<irk. Fig. 24. machine for use. Widening the gap increases voltage at the expense ofthe amperage; narrowing the gap increases amperage at the expense ofthe voltage. The wattage remains the same. For X-ra}- work the gapshould l)c as short as possible, without reducing the voltage to a pointwhere the current will not pass through the X-ra} tube. The ideal current U^x exciting an X-ray tube (in other words, pro-ducing X-ra\s) is a uni-directional one. C\)mpared with that of thehigh-fre(|uency c<)il the current of the induction coil more nearly ap-l)r(^aches this ideal, liccause of tliis, the writer advises the use of theinduction coil in preference to the high-fre(|uency coil, unless a verysmall machine is desired. We thus eliminate large high-fre(iuenc\ coilsfrom further consideration. The small, portable, suitcase, high-fre(|uency coils called X-rayand high-frequency coils, may be used where the lack of space makesthe installment of a larger machine i
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