The role of the resistor in an electrical circuit

resistor doubt!

does the resistor in a circuit resists the voltage or the current(amp).

Re: resistor doubt!

Resistor resist or opposes the flow of the current in the circuit

resistor doubt!

not the voltage!

resistance doubt!

guys i took a power source of 5.7V/800mA and load of 12VDC motor!
i connnected both ,the motor was running quite fast!
then i took a 1Ω resistor and placed between the +ve terminal of the battery and the motor,there was no resistance,and the motor was running like before,and then i placed a 33K resistor instead 1Ω resistor,and switched on the power supply,but the motor was not running. did the 33K resistor resisted the 5.7V or the 800mA.what was the problem.please help me guys!

Re: resistor doubt!

it just limits the current

Re: resistance doubt!

it resisted the current

Re: resistance doubt!

You have in effect a current limiter with the maximum current of V/R. The motor will not run with severely limited current. Try manually rotating the motor shaft and even that help will not make it run on its own.

The best way to control the motor speed is with a pulse width modulator.

resistor doubt!

Voltage is the result of resisting the current

Re: resistor doubt!

True, the resistor resists but its real effect is to cause a voltage drop. With the resistor in series with the motor, the voltage dropped across the resistor will depend on its value and the effective resistance of the motor. I say effective resistance because it isn't the same as measuring the resistance of the motor when stationary. The supply voltage will be shared by these two devices. If the resistor is a relatively low value (the 1R you tried), most of the voltage will be presented to the motor and it runs at about full speed. When you tried the 33k resistor, that is much higher than the motor effective resistance so most of the voltage is presented to the resistor. The motor gets hardly any voltage and doesn't run.

If you experimented further, you would find a resistor value that causes the motor to run slowly. I would suggest trying something less than 1k, maybe around 100R.

This is the principle used to control Scalextric cars. You don't really need any fancy cotrol circuit.

3phase.