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Thanks. Is Kirchoffs Laws a big part of the test? Will we be asked to state his laws?

I cannot speak on whether you will need to state the laws or not. If you are concerned about it, I would suggest making an effort to be prepared to do it. Although, you really should be familiar with them anyway to be able to analyze circuits, as you might receive a circuit that to calculate a measurement you must use one or more of those laws.

Thank you so much.

So I noticed that on ichaelm's Shock Value test on the Test Exchange, the answer to the first question: "What is the charge of an electron?" is in coulombs, so it is 1.60217646 Coulombs. Does anyone know what the charge of a proton in coulombs is? Also, would this be tested at State or anything, or is it possibly too trivial? And if it is on my State test, then do you think I should round or write down the whole thing with all the decimal places?

The charge of a proton is the exact same charge as an electron. I cannot speak on what any particular event supervisor will or will not expect, although I would personally assume, especially since you are only allowed one page of reference materials you would not be expected to know it to more than maybe 1.602 or so. I also believe you mean 1.602...*10^-19.

Anyone going to be at California States this weekend? Who all has competitions left? Excited?

Thanks!!!

And yeah, I have California States this weekend...

In another thread Prelude to Death asked me a question about a lab.

I'm going to ask the question in general for anyone interested in solving it, and then can provide an answer for those interested

Essentially, how do you measure the internal resistance of a battery? You only have a resistor, a multimeter and you are not supposed to use the ampmeter function of the multimeter (although that solution has value as well)

If anyone has other questions about the lab (or the other part) feel free to ask

-Sean Keenan

sean9keenan wrote:In another thread Prelude to Death asked me a question about a lab.

I'm going to ask the question in general for anyone interested in solving it, and then can provide an answer for those interested

Essentially, how do you measure the internal resistance of a battery? You only have a resistor, a multimeter and you are not supposed to use the ampmeter function of the multimeter (although that solution has value as well)

If anyone has other questions about the lab (or the other part) feel free to ask

-Sean Keenan

You measure the voltage across the resistor in series with the battery and take that value from the voltage of the battery (This gets you the voltage across the internal resistance of the battery.). Then you find the current across the resistor and use Ohm's Law to determine the internal resistance. You can check your work by finding the total resistance and using Ohm's Law to see if the current is the same across all components in the circuit. For this lab, the proctors must have a tolerance on answers due to the fact that not all resistors have the resistance that they are marked with (This is the purpose of the tolerance band on a resistor.).

space scientist wrote:

sean9keenan wrote:In another thread Prelude to Death asked me a question about a lab.

I'm going to ask the question in general for anyone interested in solving it, and then can provide an answer for those interested

Essentially, how do you measure the internal resistance of a battery? You only have a resistor, a multimeter and you are not supposed to use the ampmeter function of the multimeter (although that solution has value as well)

If anyone has other questions about the lab (or the other part) feel free to ask

-Sean Keenan

You measure the voltage across the resistor in series with the battery and take that value from the voltage of the battery (This gets you the voltage across the internal resistance of the battery.). Then you find the current across the resistor and use Ohm's Law to determine the internal resistance. You can check your work by finding the total resistance and using Ohm's Law to see if the current is the same across all components in the circuit. For this lab, the proctors must have a tolerance on answers due to the fact that not all resistors have the resistance that they are marked with (This is the purpose of the tolerance band on a resistor.).

Exactly, although you can also measure the resistance of the external resistor using the multimeter (even though you are told the resistance) Ultimately however if you did not so sufficient work you did not get very much credit on the problem. If you had the right ballpark answer (order of magnitude) and showed sufficient work then you would get credit. However, many teams (almost all) used the ohmmeter function of the multimeter directly on the battery, which doesn't work.

Does anyone know why using the ohmmeter function directly across the battery does not work?