Mr Appleton, A method of testing Triocle Vacuum Tubes 241 



to /„ + -- Vn sin vt. For these two oppositely directed effects to 

 dv 



be equal in magnitude we have 



tVq sin pt _ Rr 

 r + If ~ R + r 



that is 



^0 + 



dl 



dv 



dl . 

 T- Vn Sin 

 dv " 



1 



^R- 



p) - h 



R + r' 



Fig. 2. 



It will be seen that the method is self-compensating so far as 

 the effect of the resistance r is concerned so long as the impedance 

 of the coil L is small compared with R as is usually the case in 

 practice. If, however, it occurs that the impedance of L is large 

 compared with r the result is still a simple one, the value of dljdv 

 being then given by l/(i? + r). It will also be noticed that the 

 result is independent of the angular frequency p of the applied 

 alternating voltage. Thus a sinusoidal voltage is not essential and 

 a buzzer source may be used. 



