To determine the current across the parallel resistance, the equivalent 
nesuisicance Or Ra + R3 is found by using the reciprocal of the reciprocals 
formula where: 
R = ae 
eq 
iL al 
= + = 
HD B3 
Req = ak 
al ny od 
200 7400 
Reta sa iL = als = 195 ohms. 
6 = =—2 = SS SSE 2S 
OROOSM OF O00 13 0'.005133 
The parallel circuit Ro + R. has an equivalent resistance of 195 ohms, and 
is now treated along with Rj as part Ova ySerilesicLrcuist),. SOmthat Rp = RL + R, 
or Rp = 30,000 + 195 = 30,195 ohms. q 
The total current is in =E = TL st or 0.0000464 amp. X 10° = 46.4 pa. 
Rn 30195 ohms 
To find the current in the meter (R3), which is a branch of the parallel 
circuit, determine the voltage across the circuit from the equivalent IR drop; 
then divide this voltage by the resistance of Bey the meter element. 
I eR 
Tel 
E = 0.0000464 amp. X 195 ohms 
E = 0.009 volts, then: 
E =O COOMA ais 
7400 ohms 7400 ohms 
meter current I = 
@.000012 amp. © 10° = 1.2 ne. 
Thus, 1.2 pa will be the needle deflection on the recorder. 
Semiconductors 
A semiconductor may be described as a material with an electrical conduc- 
tivity between that of a metal and an insulator; i.e., between extremely high 
and almost no conductivity. .Its conductivity increases as the temperature 
increases, whereas with a metal, the conductivity decreases as the temperature 
increases. Each semiconductor described here may be thought of as a variable 
resistor in which the resistance to flow of current changes with the correspond- 
ing change of the physical environment; e.g., the increase or decrease of 
light, temperature, or pressure, as described in this paper (figs. 7 and 8). 
Humidity is not considered since a really efficient solid-state device depend- 
ent on humidity has not yet been developed. 
