Re: HELP!! Need answers for test!!!

["Robertm" <Respond@xxxxxxxxxxxxx>]

"Frank Olson" <Use_the_email_links@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:wjImf.82200$ki.61030@xxxxxxxxxxx
> Robertm wrote:
>> "Frank Olson" <Use_the_email_links@xxxxxxxxxxxxxxxxxxxxxx> wrote in
>> message news:YVGmf.86520$Gd6.37113@xxxxxxxxxxx
>>
>>>petem wrote:
>>>
>>>>I do not agree and this link will say the same
>>>>
>>>>http://www.answers.com/topic/resistor
>>>>
>>>>a resistor is limiting current not voltage
>>>
>>>
>>>They're wrong.  A resistor drops voltage and is a voltage limiting
>>>device. If you (for instance) use a variable resistor to control the
>>>speed of a fan (or light), the current remains the same regardless of the
>>>setting. The only thing you're doing is reducing the voltage to the load.
>>
>>
>> We are also reducing the current if the resistance of the load remains
>> fixed. A lamp and fan would be more difficult to calculate because
>> impedance enters into fan calculations, and lamp resistance changes
>> dependent on element temperature which is dependent on applied voltage
>> and subsequent current. If we were to assume a resistive load of 12 ohms
>> across a 12 volt supply, we have one amp flowing. Add a 12 ohm resistor
>> in series with the load and we now have 6 volts across the limiting
>> resistor and 6 volts across the load giving us a current of 500 ma
>> through the load.
>
> What???  Current in a series circuit stays the same.  Halving the voltage
> through the load in the series circuit you describe above doesn't reduce
> the amount of current drawn from the source.  Where did you go to skool??

Let's illustrate with some numbers. I=E/R and the current is the same in all
parts of a series circuit. If we initially have only a 12 ohm load across a
12 volt supply, we have 12/12= 1 amp. If we then add a 12 ohm resistor in
series with a 12 ohm load, we then have 24 ohms in the circuit and 12/24=
0.5 amps. You will drop 6 volts across the series resistor and 6 volts
across the load. The current will be half of what it initially was, assuming
a resistive load. That's what they taught me in school.

Bob