. The American journal of roentgenology, radium therapy and nuclear medicine . vel as astarting point for measuring levels. When anelectric charge tends to move to or from theearth the body on which this charge islocated is said to be at a potential of a cer-tain number of volts. If a point on any con-ducting system is joined by a conductingpath to the earth that point is said to bebrought to zero potential, or is grounded. The function of a generator, battery, dy-namo, or transformer is to create differencesof potential by the separation and movementof charge, thereby causing and maintaininge
. The American journal of roentgenology, radium therapy and nuclear medicine . vel as astarting point for measuring levels. When anelectric charge tends to move to or from theearth the body on which this charge islocated is said to be at a potential of a cer-tain number of volts. If a point on any con-ducting system is joined by a conductingpath to the earth that point is said to bebrought to zero potential, or is grounded. The function of a generator, battery, dy-namo, or transformer is to create differencesof potential by the separation and movementof charge, thereby causing and maintainingelectric current when conditions permittransfer of charge by any outside conductingpath. To illustrate, consider first the primarycircuit of the usual .r-ray transformer. Thegenerator (Fig. i) causes a voltage or po-tential difference of 220 volts between itsterminals; a portion of this may be used inthe control resistance, the rest is consumedin the primary. This distribution is cjuite in-dependent of the potential of any part of 434 Electrical Dangers in X-Ray Laboratories. this system as referred to the earth. In factthe entire system may be insulated fromearth and given a static charge to thousandsof volts and operate just as before. If now we join any single point to earth,as at Q, that point acquires earth or zeropotential. Assuming a good conductor be-tween O and A, the latter point will likewisebe at zero potential and P will differ fromQ by 140 volts, while B will be 220 volts RESISTA/ZCe PIp PRIMARy Ff\RTH i » Fig. I. Effect of Grounding One Side of thePrimary Circuit Operating an X-ray Trans-former THROUGH Resistance. Potential difference between earth and line G toK, 220 V. Potential drop in resistance 80 difference between lines C, F and earth,140 V. Fall in potential through primary, 140 another point, as P, may seriously dis-turb electrical conditions, depending on the resis-tance of path PEQ. above or below zero. Grounding a secon
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