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


"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



.

Relevant Pages

  • Re: Phase splitter with capacitance load.
    ... have the same output voltage, EL, as they stand, if a further load is ... The IEEE Dictionary of electrical terms defines impedance, ... Consider the following resistor network. ... Now let's apply some additional load at nodes 2 ...
    (rec.audio.tubes)
  • Re: Flyback transformer design confusion!!
    ... When applying a constant DC voltage across a resistive ... load, just *how* can I increase the power into that load, other than by ... Iout is to change the resistor. ...
    (sci.electronics.design)
  • Re: Flyback transformer design confusion!!
    ... When applying a constant DC voltage across a resistive ... load, just *how* can I increase the power into that load, other than by ... Iout is to change the resistor. ...
    (sci.electronics.design)
  • Re: HELP!! Need answers for test!!!
    ... A resistor drops voltage and is a voltage limiting device. ... We are also reducing the current if the resistance of the load remains fixed. ... through the load in the series circuit you describe above doesn't reduce the amount of current drawn from the source. ...
    (alt.security.alarms)
  • Re: 1.5V bypass
    ... that will mess up the voltage divider and lower your voltage. ... use two diodes and a series resistor to get the lower voltage, ... This will give you a fairly steady 1.4V or so with a load current ... battery voltage, but it's very wasteful of power. ...
    (sci.electronics.basics)