An elementary book on electricity and magnetism and their applications . a highpotential or pressure constitutes apositive charge, and electricity atrest at low potential or pressureconstitutes a negative terms, positive and negativecharge, must be taken as relativeterms, exactly as are the termshigh and low potential. An elec-trometer is an instrument formeasuring the attraction betweentwo charges. Electrometers made for com-mercial use in the measurementof voltage are usually called electrostatic voltmeters. Figure108 shows the construction of one example of this type of volt-me
An elementary book on electricity and magnetism and their applications . a highpotential or pressure constitutes apositive charge, and electricity atrest at low potential or pressureconstitutes a negative terms, positive and negativecharge, must be taken as relativeterms, exactly as are the termshigh and low potential. An elec-trometer is an instrument formeasuring the attraction betweentwo charges. Electrometers made for com-mercial use in the measurementof voltage are usually called electrostatic voltmeters. Figure108 shows the construction of one example of this type of volt-meter which is commonly used to measure differences of poten-tial of 1000 volts or more. The vane A A is a paddle-shapedplate of aluminum supported by knife edges at its quadrants II are both behind and in front of it and soplaced that, when a difference of potential exists between themovable vane and the stationary quadrants, the vane is at-tracted from its normal position and moves its pointer over agraduated scale. The movable vane is connected to one side. Fig. 108. — Construction ofelectrostatic voltmeter. 174 ELECTRICITY AND MAGNETISM of the line and the stationary quadrants to the other position of the pointer is controlled by gravity, littleweights being hung on a projection of the axis of the movablevane. It does not matter whether the vane is positively chargedand the quadrants negatively charged, or vice versa; an at-traction between the two will always take place and thereforethe instrument can be used equally well on d-c. and a-c. cir-cuits. It should also be remembered that this type draws aninappreciable amount of current from the line and consequentlydoes not waste any power. 125. Indicating wattmeter. The electric power which isused in any part of a direct-current circuit may be determined
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
