165
2.65 Electrometer
Circuit 139:
Electrometer with LED
Setup information
Install the two transistors, the diode, the ceramic capacitor and two resistors as shown in
Fig. 2.139
The six
jumper wires come next followed by the jumper, which serves as a switch (shown dashed). For your guid-
ance, we labelled the “switch” with
charge
and
discharge
. Check the placement on the board again and
only then connect the battery.
Components required:
2 x 2N3904 transistors,
1 x red LED, 2 x 1 k
Ω
resis-
tors, 1 x 10 nF ceramic
capacitor, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.139:
Electrometer with
LED
Experiment
If everything is wired correctly, switch to
charge
. The red LED is dark. The ceramic capacitor is charged in
no time. This means that the capacitor’s electrodes have accumulated as many electrons as possible. In our
case, we are talking about six hundred billion of electrons. This is a sheer inconceivable number, and yet,
all these electrons can flow through your skin without causing you any harm. You won’t feel anything at all.
The electrical energy contained in these electrons would just be enough to lift a mass of one thousandth of
a gram or 0.05 millimetres. That is not much power, and yet our circuit clearly shows this amount of charge.
Shift the switch to
discharge
. The red LED flashes only once, but effectively.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.139.
Summary of Contents for ELECTRONICS EXPERIMENTS BOX
Page 4: ......
Page 265: ...267 Fig 3 56 Cir cuit 56 Audio limiter Fig 3 57 Circuit 57 Amplifier for a storm detector...
Page 269: ...271 Fig 3 64 Circuit 64 Stabilizer for 1 9 V Fig 3 65 Circuit 65 Stabilizer for 2 5 V...
Page 275: ...277 Fig 3 80 Circuit 80 Quiztimer 30 seconds Fig 3 81 Circuit 81 Handy diode tester...
Page 315: ...317 Fig 3 179 Circuit 179 HF generator 150 kHz Fig 3 180 Circuit 180 HF generator 420 kHz...
