Teachers' guide 2 - National STEM Centre

Apparatus, materials, and reagents
The potentiometer wire is calibrated before use by noting the length of wire
corresponding to a known e.m.f. from a standard cell. If a standard cell such as
the Weston is not available, a mercury cell is a possible substitute. The Mallory
RM-I or RM-1R is suitable for this.
There are several ways in which suitable apparatus can be obtained.
a Standard Physics apparatus can be bought, or borrowed from the
Physics Department. For each potentiometer the following materials will be
needed:
2 keys for making and breaking the circuit
1 straight wire potentiometer, 100 cm 3 , 0.050 cm -1 with jockey
1 centre zero galvanometer (sensitivity at least 10 pA per division)
1 protective resistance for galvanometer, approximately 10000
1 2 V accumulator
Leads
Standard cell, Weston or mercury battery
b Many of the components required for a straight wire potentiometer can
be made quite cheaply.
100 cm 3 Constantan wire (S.W.G. 28) can be mounted on a suitable length of
wood together with a metre rule.
A meter, switches and terminals can be mounted in a polythene box on the lid
of which the circuit is clearly shown as in figure A.19.
Figure A.19
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