The voltage drop times the current is the electrical power being dumped into the resistor. This causes the resistor to heat up, not the other way around. Heating a resistor won't cause current thru it or voltage across it. The voltage drop is what resistors do when current flows thru them. One way to think about that is it's simply that way by definition of what a resistor is:. Another way to think about it is that the voltage is the force required to squeeze the current thru the resistor.
Higher resistances resist current more, so require a larger force more voltage to make the same current pass thru. To use the water analogy, a resistor is like a constriction in a pipe. More flow thru the pipe means more pressure across the constriction. Conversely, more pressure across the constriction means more flow thru it. If we drop right down to basic physics, we find that both Charge and Energy are quantities with a Conservation Law.
So we can be safe in taking these as having some sort of fundamental existence. Voltage OTOH is not mentioned at all. Voltage only appears as a defined quantity that's handy to work with, as the potential energy of an electrical field. Voltage is defined as the change of energy associated with the movement of a charge to within a scaling factor and dimension depending on what units we are using for energy and charge and whether it's per charge or absolute.
So when we push some charge a current flowing for some time through a resistor, see a voltage across it, and see energy released as heat from the resistor, it's not even appropriate to ask whether the heat causes the voltage or vice versa , the voltage is just a definition of what is happening with the charge movement. If we have a conductor through which no energy is associated with the movement of charge, then there is no voltage drop across it Andy , and it's called a superconductor.
An analogy is height, potential energy for a gravitational field, change of which is the energy associated with moving a mass. A superconductor is like an air table, where the mass can slide sideways without a change of potential energy. Letting it drop against a frictional restraint generates heat in the 'frictor'. The definition of voltage and the gravity analogy works for storage of energy in capacitors, inductors, height and velocity as well, but let's keep it simple for the moment with just finite or zero resistance.
I'll just leave it here as an illustration to the other answers:. The image is taken from here. Some attribute it to Eberhard Sengpiel. You need to see this at an atomic level.
Current flows due to the flow of electrons in the direction opposite to its flow. Now electrons flow due to presence of valence electrons in the valence band. So consider two scenarios. A copper wire across a battery short circuit , and the potential difference across the battery terminals be 10 electrons not the usual volt notation, simplifying the definition of voltage here. Voltage reflects the amount of work needed to move an electric charge within a circuit of components.
Work is measured in joules per unit of charge which is required to create a continuous flow of electrons. A 9-volt battery, for example, does 9 joules of work per coulomb of charge. The battery performs work, which is divided among the various components in the system. While a battery provides energy for moving the charge, components consume energy. This change results in a voltage drop. The more resistance in a circuit, the more work or voltage is required to move the charge as current flow.
Polarity reflects how the current flows from positive to negative within a circuit. While current flows from the positive to the negative terminal, electrons flow from a negative to a positive direction. A resistor consumes energy regardless if a charge enters the component as positive or exits as negative.
Voltage usually drops across all passive elements, such as resistors. Whatever resistances current encounters along the way simply add up to give the total resistance of the circuit as a whole:. Parallel circuit : In this case, a primary wire branches shown as right angles into two or more other wires, each with its own resistor. In this case, the total resistance is given by:. If you explore this equation, you find that by adding the resistances of the same magnitude, you decrease the resistance of the circuit as a whole.
By Ohm's law, this actually increases the current! If this seems counterintuitive, imagine the flow of cars on a busy highway served by a single tollbooth that backs up traffic for a mile, and then imagine the same scenario with four more tollbooths identical to the first.
This will plainly increase the flow of cars despite technically adding resistance. If you want to find voltage drops across individual resistors in a series, you proceed as follows:.
What is the voltage drop across each resistor? Now, use the current to calculate the voltage drop across each resistor. In this case, the story is simpler: Regardless of the resistance value, the voltage drop across each resistor is the same, making the current the variable that differs across resistors in this case. See the Resources for an example of an instance in which you can use an automatic tool to calculate the voltage drop in a kind of circuit arrangement called a voltage divider.
Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont.
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