166
Circuit 140:
Electrometer with moving-coil instrument
Setup information
Install the two transistors, the ceramic capacitor and two resistors as shown in
2.140.
The seven jumper
wires come next followed by the jumper, which serves as a switch (shown dashed). For your guidance, we
labelled the “switch” with
charge
and
discharge
. Last but not least, connect the moving-coil instrument.
Check the placement on the board again and only then connect the battery.
Components required:
2 x 2N3904 transistors,
1 x 1 k
Ω
resistor,
1 x 4.7 k
Ω
resistor,
1 x 10 nF ceramic capaci-
tor, 1 x moving-coil instru-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.140:
Electrometer with
moving-coil instrument
Experiment
If everything is wired correctly, switch to
charge
. The moving-coil instrument needle is not moving. In no
time the ceramic capacitor is fully charged. This means that the capacitor’s electrodes have accumulated
as many electrons as possible. In our case, we are talking about one 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 one thousandth of a millimetre. That is not much
power, and yet our circuit clearly shows this charging amount. Shift the switch to
discharge
. The needle of
the moving-coil meter moves a tiny bit.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.140.
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...
