## Methods of Measuring Electrical Resistance |

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### Common terms and phrases

accuracy accurate adjusted alternating current ammeter amperes ance apparatus arrangement balance battery bridge wire bus-bar cable capacity cell cent conductivity circuit condenser conductor connections constant copper cross-section current thru curve deflection instrument determined direct current distance electrical electrical resistance electrodes electrodynamometer electrolyte equal fall of potential fault faulty wire figure of merit give given Hence high resistance inductive insulation resistance internal resistance known resistance lead wires length located loop low resistance manganin measuring the resistance megohms ment metal meter meter-gram standard methods of measuring millivoltmeter obtained ohms platinum plug pointer potential points precision quantity ratio arms ratio coils reading relative error resistance measurements resistance thermometers rheostat sample sensibility shown in Fig shunt slide wire slide-wire bridge specific resistance spools telephone temperature coefficient terminals thru the galvanometer tion total resistance unit varied voltmeter volts Wheatstone bridge winding zero

### Popular passages

Page 96 - The rule therefore for obtaining the greatest galvanometer deflexion in a given system is as follows : Of the two resistances, that of the battery and that of the galvanometer, connect the greater resistance so as to join the two greatest to the two least of the four other resistances.

Page 84 - ... are connected giving the value 0, if between the blocks 2 and 5, the points 2 and 5 are connected giving the value 1 and so on. The value 9 is obtained when the plug is disposed of by being inserted in the last pair of blocks which have no connections.

Page v - While it is not claimed that the work is exhaustive, the author has selected for presentation all methods which in his judgment are useful...

Page 294 - Fig. 367, which is wound in a circle and is about 100 ohms. By a special construction, it is arranged so that contact can be made at any point along it, and it is therefore equivalent to a high resistance wire. It has a moving contact C and a scale of 1000 divisions. In series with this, there are the two resistances E and R. E has exactly the same resistance as the wire AR.

Page 365 - By definition, n is the ratio of the circumference to the diameter of a circle (see Section ccc 14-L).

Page 207 - This ratio may take a value of two or more. It should be clearly understood just what is meant by the quantity R which this method measures. It is a quantity which, expressed in ohms and multiplied by the square root of the mean square value of the alternating current through the circuit, expressed in amperes, will give the square root of the mean square value of that component of the impressed emf expressed in volts which is in phase with the current. Or, it is the quantity which, when multiplied...

Page 84 - Fig. 503b shows the method of connecting these points two at a time, with the use of a single plug. The circles in the diagram represent two rows of ten brass blocks each. To the first two blocks at the top of the rows, the points 5 and 1...

Page 83 - If the points (2) and (5) are connected the 3, 31 and 2 ohm coils will be short circuited and the current will traverse 1 ohm. By extending this process so that we connect two and only two points at a time, it is possible to obtain the regular succession of values n (0, 1, 2, 3, 4, 5, 6, 7, 8, 9), the last value being obtained when no points are connected. The following table shows the points which must be connected to obtain each of the above values and the coils which will be in circuit for giving...

Page 332 - ... volts and the b' terminal at 220 volts; thus the current in the AL coil, which in this case is the magnetizing current of the core, is due to a potential difference of 20 volts. The strength of this current will be found by Ohm's law, namely the quotient of the EMF, or difference of potentials between the terminals of the coil, divided by the resistance of the coil — in this case = -ffa, that is T\j- ampere.

Page 297 - ... Extending the investigation to solutions of cadmium sulphate we obtain a cell in which the heat of dilution is relatively large. The study of this cell was taken up in the general manner just described. The amalgam, however, proved more troublesome. With dilute amalgams, the EMF did not consistently return to the same value when brought back to the same temperature. Evidently some change had taken place either in the amalgam or the electrolyte. Since there is no transition point in cadmium sulphate...