I saw on this site that a passive device is one that is incapable of controlling current by an external power supply. I thought a resistor can then not be a passive instrument since a reistor can control current when a power supply is connected to it. Recall - Ohm's Law. I'll love you to explain better on this issue. Thanks

 

Resistor is a passive device. In the power supply work as SENSOR. (give a current-depending voltage) For the CONTROLING still need an active device.

 

Generally, a passive device is one that does not contribute free electrons to a given circuit. An active device does contribute electrons to a given circuit (we call this amplification). A resistor is a passive device since it does not contribute electrons to a circuit. In fact it "steals" electrons from the circuit and converts them into heat!

Originally posted by Sebi@Oct 10 2005, 02:47 AM
Resistor is a passive device. In the power supply work as SENSOR. (give a current-depending voltage) For the CONTROLING still need an active device.

[post=10900]Quoted post[/post]​

 

Originally posted by viterbi@Oct 13 2005, 08:59 PM
Generally, a passive device is one that does not contribute free electrons to a given circuit. An active device does contribute electrons to a given circuit (we call this amplification). A resistor is a passive device since it does not contribute electrons to a circuit. In fact it "steals" electrons from the circuit and converts them into heat!

[post=10979]Quoted post[/post]​

surely no electrons can be lost in the circuit by the resistor. What is being lost is energy by the action of pushing electrons through the resistor. if electrons were to be lost you would cause the atoms in the conductor to be +ively charged and stop the circuit being a circuit as there would be no easily removable electrons to transfer energy

 

Originally posted by mentaaal@Oct 17 2005, 07:23 PM
surely no electrons can be lost in the circuit by the resistor. What is being lost is energy by the action of pushing electrons through the resistor. if electrons were to be lost you would cause the atoms in the conductor to be +ively charged and stop the circuit being a circuit as there would be no easily removable electrons to transfer energy

[post=11065]Quoted post[/post]​

Energy required for pushing the electrons through the resistor is VOLTAGE. But something is converted in to heat .....is it voltage. ???? or power...if power P=VI , current is converted in to heat. current is the flow of electrons....so electrons should be converted in to heat.....(so circuit stops) or is it voltage??? we know H=I(square)RT.
I=V/R. so whether voltage is converted in to heat......????

so i think the heat is produced due to the collision of both +ve and -ve ly charged particles.....for collision of electrons both voltage and current(flow of electrons due to voltage difference) is required...ie nothing but power....so power is converted in to heat.

 

Originally posted by jidhishs@Oct 20 2005, 11:11 PM
Energy required for pushing the electrons through the resistor is VOLTAGE. But something is converted in to heat .....is it voltage. ???? or power...if power P=VI , current is converted in to heat. current is the flow of electrons....so electrons should be converted in to heat.....(so circuit stops) or is it voltage??? we know H=I(square)RT.
I=V/R. so whether voltage is converted in to heat......????

so i think the heat is produced due to the collision of both +ve and -ve ly charged particles.....for collision of electrons both voltage and current(flow of electrons due to voltage difference) is required...ie nothing but power....so power is converted in to heat.

[post=11151]Quoted post[/post]​

Energy is measured in Joules, not Volts. Electromotive Force is measured in Volts. Voltage is Energy Per Unit Charge. One Volt equals One Joule Per Coulomb of Charge.

"Heat" is defined as energy in transit from a higher temperature object or system to a lower temperature object or system. Heat is also measured in Joules.

Heat and Work are interchangeable. Work is also measured in Joules.

Power is the rate at which energy is expended or the rate at which work is done. Power is the rate at which heat is dissipated.

One Watt is equal to One Joule Per Second.
One Joule is equal to One Watt-Second.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

 

Passive and active devices are characterised by their control on the circuit operation, typically the control of current flow.

From All About Circuits:

An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). In order for a circuit to be properly called electronic, it must contain at least one active device. Components incapable of controlling current by means of another electrical signal are called passive devices. Resistors, capacitors, inductors, transformers, and even diodes are all considered passive devices. Active devices include, but are not limited to, vacuum tubes, transistors, silicon-controlled rectifiers (SCRs), and TRIACs. A case might be made for the saturable reactor to be defined as an active device, since it is able to control an AC current with a DC current, but I've never heard it referred to as such. The operation of each of these active devices will be explored in later chapters of this volume.

All active devices control the flow of electrons through them. Some active devices allow a voltage to control this current while other active devices allow another current to do the job. Devices utilizing a static voltage as the controlling signal are, not surprisingly, called voltage-controlled devices. Devices working on the principle of one current controlling another current are known as current-controlled devices. For the record, vacuum tubes are voltage-controlled devices while transistors are made as either voltage-controlled or current controlled types. The first type of transistor successfully demonstrated was a current-controlled device.

Source: http://www.allaboutcircuits.com/vol_3/chpt_1/2.html

It is worth checking Volume 3: Chapter 1 of the on-line textbook.

 

You may also be interested in the following articale from wikipedia titled "Active vs Passive Elements":

http://en.wikibooks.org/wiki/Circuit_Theor...assive_Elements