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

[Frank Olson <Use_the_email_links@xxxxxxxxxxxxxxxxxxxxxx>]

Robertm wrote:
> "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.


They taught the same thing in my school.  I saw the 1 amp load in your
first example as being fixed (current in a series circuit is constant).
  You are correct (in all respects).  Chalk it up to a "blonde
moment"...  :-)