This voltage can be produced by static electric fields, by electromagnetic fields, by time varying magnetic fields. To measure the voltage in a closed circuit we use a voltmeter. Voltage in a closed circuit in the sense it is either from a source of energy or from stored energy or lost energy. To make it more clear to you we can compare this voltage, current, resistance in a closed circuit to the water tank.
That is a closed circuit with active and passive elements is analogous to a water tank. In this water pressure is compared to voltage , water flow is analogous to current, the amount of water is analogous to charge.
If more water in the tank then more charge and more pressure then more electric pressure. Let us consider two points A and B. Current is measured through a component.
Potential difference is the energy used between two points in a circuit, therefore it is measured between two points either side of a component. We describe this as the potential difference measured across a component. This diagram shows that an ammeter must be connected in series with the components you want to measure and a voltmeter must be connected in parallel.
When such a battery moves charge, it puts the charge through a potential difference of The total energy delivered by the motorcycle battery is. While voltage and energy are related, they are not the same thing. The voltages of the batteries are identical, but the energy supplied by each is quite different. Note also that as a battery is discharged, some of its energy is used internally and its terminal voltage drops, such as when headlights dim because of a low car battery.
The energy supplied by the battery is still calculated as in this example, but not all of the energy is available for external use. Note that the energies calculated in the previous example are absolute values.
The change in potential energy for the battery is negative, since it loses energy. These batteries, like many electrical systems, actually move negative charge—electrons in particular. The batteries repel electrons from their negative terminals A through whatever circuitry is involved and attract them to their positive terminals B as shown in Figure 2. Figure 2. A battery moves negative charge from its negative terminal through a headlight to its positive terminal.
Appropriate combinations of chemicals in the battery separate charges so that the negative terminal has an excess of negative charge, which is repelled by it and attracted to the excess positive charge on the other terminal. In terms of potential, the positive terminal is at a higher voltage than the negative.
Inside the battery, both positive and negative charges move. When a To find the number of electrons, we must first find the charge that moved in 1. The number of electrons n e is the total charge divided by the charge per electron.
That is,. This is a very large number. It is no wonder that we do not ordinarily observe individual electrons with so many being present in ordinary systems. In fact, electricity had been in use for many decades before it was determined that the moving charges in many circumstances were negative. Positive charge moving in the opposite direction of negative charge often produces identical effects; this makes it difficult to determine which is moving or whether both are moving.
Figure 3. A typical electron gun accelerates electrons using a potential difference between two metal plates. The energy of the electron in electron volts is numerically the same as the voltage between the plates. For example, a V potential difference produces eV electrons. The energy per electron is very small in macroscopic situations like that in the previous example—a tiny fraction of a joule. But on a submicroscopic scale, such energy per particle electron, proton, or ion can be of great importance.
For example, even a tiny fraction of a joule can be great enough for these particles to destroy organic molecules and harm living tissue. The particle may do its damage by direct collision, or it may create harmful x rays, which can also inflict damage. It is useful to have an energy unit related to submicroscopic effects. Figure 3 shows a situation related to the definition of such an energy unit. An electron is accelerated between two charged metal plates as it might be in an old-model television tube or oscilloscope.
The electron is given kinetic energy that is later converted to another form—light in the television tube, for example. Note that downhill for the electron is uphill for a positive charge. On the submicroscopic scale, it is more convenient to define an energy unit called the electron volt eV , which is the energy given to a fundamental charge accelerated through a potential difference of 1 V.
The current means the rate of flow of electric charge. This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions. The SI unit for measuring the rate of flow of electric charge is the ampere. Electric current is measured using an ammeter.
Current is usually abbreviated "I" "C" is reserved for the principle of charge , the most fundamental building block of electricity. Current is measured in amperes or amps , abbreviation "A". Current refers to how much electricity is flowing--how many electrons are moving through a circuit in a unit of time. The resistance of an object is a measure of its opposition to the passage of a steady electric current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material.
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