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

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"... :-)
.

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