Student "edition" found at {csi dot journalspace dot com}.

Maybe I shouldn't have started this blog now, not with everything that's been going on.

On the third day of the eleventh week of classes, we had our second to the last experiment in Electricity and Magnetism lab: The Construction of Ammeters and Voltmeters.

They asked for a bonus question in the quiz again, but instead of asking for the first name of the scientist whose principle or invention we were studying, the question I gave was about what was the first quantity they were supposed to measure and record in the experiment. Because the manual had been revised, it turns out what I thought was the correct answer would have been wrong. I thought it was the number of divisions of the galvanometer, which they would need to get the sensitivity (for machines, sensitivity can be quantified, unlike for human beings, or those who pass for humans).

The first question was to give the purpose of the shunt resistor in the ammeter construction circuit. I even gave the hint of starting with the equation (which I knew some had already memorized at that point – the experiment having been delayed a week) and work it out from there.

I should have known that Deiv, of all people, would give a very literal answer and expect full credit. Yes, the shunt resistance is the galvanometer resistance times the galvanometer current over the difference of the applied or set maximum current and the galvanometer current, but there was an illustration from the manual that showed the shunt resistor shunts most of the current away from the galvanometer except for its maximum value.

At least he did his duties as secretary for this experiment, which was the first time I’ve seen him accept responsibility, when it is supposed to be the second time he is assigned that job this term.

The second question, about the multiplier resistor in the voltmeter circuit, asked for the voltage across the multiplier, not across the galvanometer as given by the equation. A little bit of analysis would have told them they had to apply resistors in series and parallel for this one.

Two groups were merged again because of the lack of DC voltage generators. I also gave them different values for the constructed ammeter and the voltmeter, and detailed instructions on how to get the new scale based on the new maximum values.

For one part they had to use a potentiometer whose value could only be determined exactly using a digital meter, and they had to set it to a specific decimal resistance value the same way. For the second part, based on their calculations, I told them to add up whatever resistors were available in the cabinet. That’s learn them applications.

Session 702 gets all its current shunted off to another branch at this point. Class dismissed.