SI: ohm Mystery Cache

The International System of Units (SI), commonly known as the metric system, is the international standard for measurement. The SI plays an essential role in international commerce and is commonly used in scientific and technological research and development. This cache is part of the SI geoart that allows you to learn about the SI units. Visit the introduction cache to learn more about this geoart.

Electric resistance: ohm (Ω)

The ohm is the SI derived unit of electric resistance. It is defined as an electrical resistance between two points of a conductor when a constant potential difference of one volt, applied to these points, produces in the conductor a current of one ampere, the conductor not being the seat of any electromotive force.

Ohm’s law

Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Therefore: I=V/R, where:

• I is the current through the conductor in amperes;
• V is the voltage measured across the conductor in volts;
• R is the resistance of the conductor in ohms.

Ohm’s law states that the R in this relation is constant, independent of the current.

Measuring resistance

Ohm’s law gives a basic method of measuring electric resistance. If we know the current through a conductor between two points, as well as the voltage across the two points, we can calculate R=V/I. For example, to measure the resistance of a flash light bulb, we can:

1. Measure the voltage of four AA batteries: 6V.
2. Measure the current through the bulb: 0.15A.
3. Calculate the resistance: 6V / 0.15A = 40Ω.

Multimeter is an instrument that can measure resistance. It isn’t too complicated, and yoursunny made one in a few hours when he was an undergrad. The multimeter has an internal battery, so that it can apply power to the conductor, simultaneously measure voltage and current, and calculate the resistance according to Ohm’s law.

This Geocache

If we connect a 63.45Ω resistor to a USB power bank, what’s the electric current through this resistor in milliamperes? Multiply by 10 and round to an integer to get ABC.

In which year was the first multimeter put on sale? Divide by 3 and subtract 93 to get DEF.

Final coordinates: N 39° 08.ABC W 077° 08.DEF

You can validate your puzzle solution with certitude.

Cache container is a baby-nano with tiny log sheet. A pair of tweezers is mandatory for log retrieval. To conserve space, please omit the date and write the first two letters of your username only.

Some hides are located along a road without sidewalk. For your safety, please walk on the grass out of the car lanes, and avoid going at night without wearing a safety vest.

Lists of Caches in SI geoart

0. introduction
1. second and hertz
2. metre
3. kilogram
4. m/s and km/h
5. mole
6. radian and steradian
7. m/s² and newton
8. m² and pascal
9. joule and watt
10. ampere and coulomb
11. volt and farad
12. ohm
13. kelvin
14. candela, lumen, and lux
15. bushel
16. foreword & afterword
17. prize distribution