Confused
Hi Tinmanpower,
I am sorry but you have some confused ideas about ohms law. Resistance does not change with a change in voltage. Also your example is incorrect.
In the first place you are overloading your power supply. You said your theoretical supply could supply 12 volts at 1 amp. If you apply that to a 10 ohm load you would get 1.2 amps which is more than your theoretical supply can supply.
Now lets try it with a 20 ohm resistor. Since we are not overloading the power supply it will now apply 12 volts to the resistor at .6 amps. This figure comes directly from ohms law:
I = V/R. Now change the resistor to 40 ohms. Now the current will drop to .3 amps but the voltage will still be the voltage supplied by the power supply = 12 volts.
Now you may be thinking about voltage drop across a resistor that is part of a circuit. Lets use a simple 12 volt DC circuit. If we have a 12 volt bulb that draws 1 amp that means the resistance of that bulb is 12 ohms. Now lets put a 12 ohm resistor in series with our bulb. We now have a total resistance of 24 ohms so our total current is now .5 amps and our voltage drop across the resistor is 6 volts. This again is from ohms law : V = IR. Now change the resistor to 36 ohms. Now our total circuit resistance is 48 ohms and therefore our current is I = V/R or .25 amps. And our voltage across the resistor is V = IR or 9 volts. So yes changing the resistance of a resistor that is part of a circuit can change the voltage drop across that resistor. But that is not the same as saying changing the voltage will change the resistance. I hope this has helped you to understand the difference.
Respectfully,
Carroll
Hi Tinmanpower,
I am sorry but you have some confused ideas about ohms law. Resistance does not change with a change in voltage. Also your example is incorrect.
In the first place you are overloading your power supply. You said your theoretical supply could supply 12 volts at 1 amp. If you apply that to a 10 ohm load you would get 1.2 amps which is more than your theoretical supply can supply.
Now lets try it with a 20 ohm resistor. Since we are not overloading the power supply it will now apply 12 volts to the resistor at .6 amps. This figure comes directly from ohms law:
I = V/R. Now change the resistor to 40 ohms. Now the current will drop to .3 amps but the voltage will still be the voltage supplied by the power supply = 12 volts.
Now you may be thinking about voltage drop across a resistor that is part of a circuit. Lets use a simple 12 volt DC circuit. If we have a 12 volt bulb that draws 1 amp that means the resistance of that bulb is 12 ohms. Now lets put a 12 ohm resistor in series with our bulb. We now have a total resistance of 24 ohms so our total current is now .5 amps and our voltage drop across the resistor is 6 volts. This again is from ohms law : V = IR. Now change the resistor to 36 ohms. Now our total circuit resistance is 48 ohms and therefore our current is I = V/R or .25 amps. And our voltage across the resistor is V = IR or 9 volts. So yes changing the resistance of a resistor that is part of a circuit can change the voltage drop across that resistor. But that is not the same as saying changing the voltage will change the resistance. I hope this has helped you to understand the difference.
Respectfully,
Carroll
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