User manual

Resistors can also be switched in parallel. A simple parallel circuit comprises
at least two resistors. Of course, several resistors can be switched in parallel
as well.
Plug two 1 kΩ resistors below each other on the experimenting board. They are
switched in parallel now. Now apply the two measuring strings to the ends of the
two resistors. Now determine the overall impedance. In our circuit, it is 493 Ω
and therefore only half of a single resistor.
Now switch a 1 kΩ resistor and a 330 Ω resistor in parallel.
The total impedance now is about 245 Ω. Try other resistor combinations as well.
When switching resistors in parallel, the overall impedance is always lower than
the smallest single impedance.
The overall impedance of resistors switched in parallel can be calculated
according to the following formula:
1 / R
ges
= 1 / R1 + 1 / R2 + … 1 / Rn
248 Ω = 1 / 1,000 Ω + 1 / 330
Ω.
To get to the overall impedance, push the button 1/x on the calculator.
Figure 31: When switching two resistors in parallel, the overall impedance is
always lower than the smallest single impedance.
Figure 32: Two resistors switched in parallel on the experimenting board
Figure 33: Two 1 kΩ resistors switched in parallel lead to an overall impedance
of 493 Ω.
The result is not precisely 500 Ω because of production tolerances in resistor
manufacture.
5 Measuring the Capacitator
To be able to measure the capacitator capacity, you need a multimeter that also
permits capacity measurements (e.g. the Voltcraft VC840).
Unfortunately, only relatively few and high-quality multimeters have capacity
measuring ranges. Standard multimeters usually only have volt, ampere and ohm
measuring ranges.
Attention!
Before connecting a capacitator to the meter, you must discharge it! For this,
short-circuit the two connections. Use pliers or a screwdriver that you put
across the tow contacts. Only hold the tool by the isolated grip. Short-
circuiting of capacitators may cause high-energy discharge. Therefore, never
touch the connections of capacitators with more than 35 V direct voltage/25 V
alternating voltage – in particular if you do not know if it is charged or not.
Caution, danger to life!
Now pug the capacitator to be tested onto the experiment field so that the two
self-made wire test prods can be placed on the experimenting board without the
two measuring device strands touching.
Capacitators to be measured must never be installed in circuits or circuit parts.