Shock Value B

JSGandora
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Re: Shock Value B

Postby JSGandora » December 27th, 2010, 7:45 pm

...since the induced EMF is the rate of change of magnetic flux wrt time.
Sorry, but what is "wrt"?

And doesn't EMF have to do with inductors which the rules said specifically was not going to be on the test?

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Re: Shock Value B

Postby andrewwski » December 27th, 2010, 8:53 pm

Wrt = with respect to.

Put in other words, the induced EMF in a loop is the change in magnetic flux over time. Since flux is constant, there is no change over time, thus induced EMF = 0.

EMF is electromotive force, more commonly known as voltage. In this case, you are correct, it has to do with induction (although not inductors specifically).

I do not have a copy of the event rules, so I do not know if induction is covered by the event or not (I would imagine if inductors are not, the topic itself isn't, but that may not be the case). I also don't have a copy of last year's rules either, so it's possible that it was a topic covered by last year's rules but not this year's.

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Re: Shock Value B

Postby ichaelm » December 30th, 2010, 7:29 am

The rules say you're supposed to know about electromagnets. You also have to know about EMF, of course; it's just another name for voltage. I usually see questions about electromagnetic induction on tests, but not about inductors as circuit components. For example, they'll expect us to know in what direction a current-carrying wire induces a magnetic field, but they don't expect us to analyze a circuit with an inductor in it. And yeah, andrewwski, you're right about my question!

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Re: Shock Value B

Postby Princessangie » December 30th, 2010, 11:08 am

ichaelm, could you please post an answer to your test on the test exchange please? Thank you!

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Re: Shock Value B

Postby --[Grand]-- » January 3rd, 2011, 9:37 pm

Could someone explain the concept of Internal resistence? A definition or some formulas would be very helpful :D

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Re: Shock Value B

Postby andrewwski » January 3rd, 2011, 11:05 pm

The internal resistance is the resistance that a power source (eg battery) has. An ideal battery would have zero internal resistance - it purely supplies voltage. However, all real batteries and power sources have internal resistance. If you're drawing them out in circuit, think of an ideal battery with a resistor in series immediately following it. The resistor actually represents the internal resistance of the source itself - it cannot be separated.

Basically, the concept of internal resistance is that batteries and power sources also have resistance.

Formulas would be no different than for any resistance - Ohm's Law, Kirchoff's Laws, etc.

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Re: Shock Value B

Postby JSGandora » January 10th, 2011, 6:22 pm

What would you recommend to put on the info sheet we get to take to competition? Would lists of different types of magnetic materials be helpful (ferromagnets, etc.)? Also, what formulas are most important?

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Re: Shock Value B

Postby --[Grand]-- » January 11th, 2011, 10:09 pm

Could you provide an example for internal resistence in a problem?

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Re: Shock Value B

Postby chalker » January 12th, 2011, 8:42 am

Could you provide an example for internal resistence in a problem?
There are some great resources we've put up on the official Shock Value website that might help you:
http://soinc.org/shock_value_b

In particular, the ibiblio book has a section on internal battery resistance: http://www.ibiblio.org/kuphaldt/electri ... DC_11.html

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Re: Shock Value B

Postby JSGandora » January 12th, 2011, 6:25 pm

What's the difference between EMF and voltage? This is probably a stupid question and I'm sorry.


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