Electrical measurementsA laboratory manual . current traversesthe galvanometer on opening and closing the batterycircuit, as well as when it is kept closed, then the two time constants are equal and L = QRO. To show that a time constant ^ is a time, since a resist- R ance has the dimensions of a velocity, and a capacity is the square of a time divided by a length, we have from the equation -^=R0(calling the coefficient of self-induc- tion L to distinguish it from a length X)J-, . L_L T_ ™ Also i=(4Y- -~ = i. ?=©??= SELF-INI)UCTIOy AND MUTUAL INDUCTION. 249 or self-induction is a length. The un
Electrical measurementsA laboratory manual . current traversesthe galvanometer on opening and closing the batterycircuit, as well as when it is kept closed, then the two time constants are equal and L = QRO. To show that a time constant ^ is a time, since a resist- R ance has the dimensions of a velocity, and a capacity is the square of a time divided by a length, we have from the equation -^=R0(calling the coefficient of self-induc- tion L to distinguish it from a length X)J-, . L_L T_ ™ Also i=(4Y- -~ = i. ?=©??= SELF-INI)UCTIOy AND MUTUAL INDUCTION. 249 or self-induction is a length. The unit of induction isthe henry and equals 10 cms. It varies directly as theohm. If C is in microfarads the value of L from the equa-tion above will bemultiplied by lO*^ to reduce to henrys. a million times too large and must be 117. Andersons Modification of Maxwells Method.^— In the preceding method of Maxwell a double adjust-ment must be made in order to effect a balance. First,one of the branches P has to be adjusted for a balance. Fig. 117. with a steady current. Then, in order to obtain a bal-ance when the galvanometer circuit is closed first, theresistance R will have to be adjusted. This necessitatesa fresh adjustment of P, and so on. Andersons modifi-cation of Maxwells method is designed to facilitate theadjustments. Suppose a balance has been obtained for steady cur-rents by closing ^^ before jSTq (Fig. 117). This balancewill not be disturbed by introducing the resistance rbetween F and iV. Adjust r therefore till the galvanom- 1 FMl. Mag., Vol. XXXI., 1891, p. 329. 250 ELECTRICAL MEASUREMENTS. eter shows no deflection when K2 is closed before K^,The potentials at H and N then remain equal to eachother. Let x be the quantity which has fiow^ed into thecondenser at the time ^, and z the quantity which haspassed through FZ. Then x -\- z has passed through if C is the capacity of the condenser, since the fallof potential from ^ to -^ is the same by the two paths,
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