| LIST OF SOME TYPICAL LAB APPLICATIONS | |
|---|---|
| Lab experiment | Function |
| Ohm's Law | voltage regulator |
| Resistivity of Metals | current regulator |
| The Temperature Dependence of Resistance | current regulator |
| Measurements of Earth's Magnetic Field | current regulator |
| Superconductivity | current regulator |
| Measurements of Faraday's Constant (Chem. Lab) | current regulator |
| Electrolysis (Chem. Lab) | current regulator |
All part numbers are taken from Radio Shack Catalog 1996.
| LIST OF PARTS FROM RADIO SHACK | ||
|---|---|---|
| part # | part name | quantity |
| 276-1778 | voltage regulator LM317T | 2 |
| 271-1101 | resistors 10 OHM 0.5 W | 2 pkg |
| 271-1301 | resistors 10 OHM 0.25 W | 1 pkg |
| 276-148 | predrilled board | 1 |
| 271-265B | rheostat 20-OHM 1.2W | 2 |
| 274-251 | 1/8" jacks | 1 pkg |
| 275-614 | toggle switch | 1 |
| 274-415 | knobs 3/4" | 1 pkg |
| 274-661 | posts | 1 pkg |
| 270-233 | box | 1 |
| 278-501 | 30-gauge wire - red | 1 |
| 278-503 | 30-gauge wire - blue | 1 |
| 64-3011 | machine screws 40-4 | 1 pkg |
| 64-3018 | machine nuts 40-4 | 1 pkg |
| 273-1652 | 12VDC adapter 500mA | 1 |
The blueprint below (Fig.1) shows how the electric circuit of the power supply looks like, and how it can be arranged on a half of the predrilled board (276-148). As usually a clean soldering with use of some sort of soldering paste like rosin soldering flux (64-021) is essential. Most constructional troubles are caused by wrong connections or bad soldering.
 |
| Fig.1 |
Additionally you have to make from an aluminum sheet two heat sinks for
both LM317T (use of heat sink grease 276-1372). The Radio Shack heat sinks (276-1363) do not fit to the 270-233 box. Alternatyvelly you may
use a larger box.
In Fig.2 a possible arrangement of controls, input and outputs is shown.
Essential here is a firm fixing of potentiometers (rheostats). They should be prevented to turn around if somebody is trying to turn them too hard.
 |
| Fig.2 |
 |  |
| This diagram shows a quick demonstration of dependence of a resistance on temperature. The current regulator keeps a steady current through the wire. This current does not depend on the wire resistance. As the wire becomes hot its resistance increases and this in turn causes an increase of the voltage on the wire. For good results the wire resistance should be a few times greater than the resistance of the other electric connectors used in this experiment. A spiral made of a thin iron wire (gauge 30) will do the trick. | This is a copy of the Oersted's experiment revealing a magnetic field around conductors with electric currents. The left side of the triple wire loop should be oriented along the magnetic needle direction when the current is absent. The needle should be as close to the wires as possible. Increasing the current gradually we will observe the magnetic needle turning away from its initial direction. This experiment can be mounted on a plexiglass plate and demonstrated to large classes with help of an overhead projector. |
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