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On Fri, 02 Dec 2005 22:37:55 +0000, Panther wrote:
>> Use a high-impedance voltmeter, like a DVM.
>>
>> Record the voltage while the balls are apart. It will very probably be
>> very close to zero. You can assure this by momentarily shorting the
>> capacitor terminals.
>>
>> Drop the ball. While the balls are in contact, current will flow and
>> start to charge the cap through the resistor, with a time constant
>> of T = RC.
>>
>> The voltage across the capacitor at the exact moment that the balls
>> separate will tell you T by using that exponential equation that I
>> can't remember now, but since you're in school you should look it up
>> anyway.
>
> Thank you!!!!!!!!!!!!!! This looks very simple so I will give it a go. But
> could you please explain what the time constant T = RC means? I've no idea.
> So you're saying, for example, if I were to do the practical now and record
> the voltages, I would be able to work out the time section using some
> formula? IE I don't need the equipment? As that would very handy.
>
T = RC is the "time constant". It's the amount of time it takes for the
charge to reach 63% (or something) of its final value, R is in ohms, and
C is in farads. With T on the horizontal axis, the cap voltage rises at
some exponential rate...
Maybe one of these sites will be more helpful:
http://www.google.com/search?q=%22time+constant%22
Good Luck!
Rich
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