Ohm's Law

  • Thread starter MitsuShai
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  • #1
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I always fail to get the concepts down or not fully state the concepts, so I would appreciate it if someone reviewed my understanding of these concepts and point of the places where I'm not getting the right idea or almost got the right idea but not completely.


1. What is wrong with this: "If current is used up going through a resistor & in a the resistor there is a constant potential difference , so why is the resistance on the resistor constant?"

Current can never be used up. Resistance is constant in a resistor because the same current always flow in the circuit.


2. If current is not used up, then what is? (we pay for electricity for some reason)
I got somewhat confused on this. Don't we pay for electricity because it's difficult to generate electricity and maybe resistance could have something to do with it? I really can't think of anything that could be used up.


3. Battery terminals have to be connected together for current to flow, why?
the terminals have to be connected, so it can be a closed circuit where current can flow from the battery and back to the battery and get sent out again in a cycle.
 
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Answers and Replies

  • #2
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For (1), Ohm's law is the answer which states that [tex]I \propto V[/tex] in a conductor while temperature remains constant. The constant of proportionality is the inverse of resistance (R) of that conductor. Ohm has done many experiements and discovered that the above relation holds in conductors and now it is called in his name.

For (2) you pay electricity bill because you consume power. Whenever current flows through resistor power is dissipated in the resistor. There could be energy conversion, for example in your room heater, that energy is converted in to heat, in your filament lamp it is converted mostly in to light and so on.

For (3) open circuit means infinite resistance. So voltage divided by infinite resistance gives zero current. That's why no current flows while circuit is open.
 
  • #3
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For (1), Ohm's law is the answer which states that [tex]I \propto V[/tex] in a conductor while temperature remains constant. The constant of proportionality is the inverse of resistance (R) of that conductor. Ohm has done many experiements and discovered that the above relation holds in conductors and now it is called in his name.

For (2) you pay electricity bill because you consume power. Whenever current flows through resistor power is dissipated in the resistor. There could be energy conversion, for example in your room heater, that energy is converted in to heat, in your filament lamp it is converted mostly in to light and so on.

For (3) open circuit means infinite resistance. So voltage divided by infinite resistance gives zero current. That's why no current flows while circuit is open.

For the first part, you're saying that the resistance is constant because the current is the same in the current and and also current and voltage are proportional, so voltage is constant too. Since R= V/I , with V/I being a constant ratio, R is also constant. Did I screw it up, ( I do that a lot)?
 
  • #4
245
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For the first part, you're saying that the resistance is constant because the current is the same in the current and and also current and voltage are proportional, so voltage is constant too. Since R= V/I , with V/I being a constant ratio, R is also constant.
Take it this way, you can apply any amount of voltage to a conductor, measure the current flowing through the conductor, now find ratio of voltages and corresponding current values. You will find that for different values of voltages applied and the corresponding V/I ratios are always the same. Since this is a constant we give it a name that is resistance of the conductor. (Remember it holds only when temperature is maintained constant.)
 
  • #5
159
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Take it this way, you can apply any amount of voltage to a conductor, measure the current flowing through the conductor, now find ratio of voltages and corresponding current values. You will find that for different values of voltages applied and the corresponding V/I ratios are always the same. Since this is a constant we give it a name that is resistance of the conductor. (Remember it holds only when temperature is maintained constant.)
Understood, Thank you very much for your help :)
 

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