# Simple Concept Circuit Question - help me! im so lost

Discussion in 'Homework Help' started by parkpika, Aug 6, 2008.

1. ### parkpika Thread Starter New Member

Aug 6, 2008
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0
I have been looking back at circuit problems and I couldnt understand something.

Imagine a simple circuit with 10V battery and 5 ohms resistor. The current would be 2.0 A in this case. If 20V battery was used with the same setup, the current would double to 4.0A since the resistance doesnt change for a resistor. If this is correct, voltage drop across the resistor would have to be 10V and 20V respectably.
1. Do all the voltage always drop and occurs across a resistor in a simple series circuit? (Does the resistor always take in every potential energy when current goes through a resistor? if so what happens in a series circuit with 2 resistors?)
2. Why is it that all the voltage drops (10V and 20V) when resistor's resistance is the same?
3. Do resistors resist only against current not voltage?

Answer to these desperate questions would be very appreciated
Thanks

May 16, 2005
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3. ### Ratch New Member

Mar 20, 2007
1,068
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parkpika.

Regardless what you read elsewhere, just remember that voltage in not force or energy (neither kinetic or potiential). Always remember that voltage is the energy density of the charge. How does this apply to your question? Whenever the energy density of some charge carriers is greater at one place than another place, the charge will try to flow to the place of lower energy density (voltage). This flow of charge is called current. Notice that current does not flow. It exists and has a direction. Only charge flows in this case. As the charge flows it encounters obstacles along the way, specifically ionic cores of the conductor, usually metal. The more obstacles encountered, the harder it is to get through the conductor. Resistance is a measure of the obstacles and difficulty for the charge to pass through. By the way, this is not a friction phenomena, it is a quantum event. The collisions and rebounds from the ionic cores of the material lattice causes the material to have a faster and greater vibration, which by quantum theory, means higher energy level and temperature. The temperature is dissipated as heat. When the charges reach the end of their passage through the conductor, they will have less energy density (voltage) because some of their collective energy was transferred to make the material lattice vibrate faster and greater.

Series or parallel, it makes no difference. Any time you send a charge through a conductor, energy is lost, and the energy density (voltage) drops.

Because twice as much current existed in the 20 volt circuit. That means twice as much energy was used, so the energy density (voltage) was reduced twice as much.

It takes energy to establish a current through a resistor. The current is established by the energy density (voltage) and the resistance. This is calculated by the resistance formula V/R. If the resistance is higher, it takes more energy to establish the same current. In a series circuit, the resistors share the energy needed to establish a current. The higher value resistors take more energy for the same value of current, so the energy density (voltage) will drop more across the higher value resistors than the lower valued ones.

Ratch

Last edited by a moderator: Aug 7, 2008