# Electric Current, Voltage, and Resistance

Electric Three primary electrical characteristics are current, voltage, and resistance. Putting it briefly,

Topics:
• Current is the directed flow of charge through a conductor.
• Voltage is the driving force behind current flow.
• Resistance is an obstruction to the current that a material, component, or circuit provides.

Electrical circuits are characterized by their electric current, voltage, and resistance. Ohm’s law, the foundational law of circuit operation, defines their connections.

## Electric Current

An extraneous force, as you probably know, can dislodge an electron from its parent atom. Free electrons can be created with very little effort in copper (and other metals). In fact, free electrons can be created by the thermal energy (heat) already present at room temperature (220C). In a linear relationship, temperature and electron production rate. As the temperature rises, the number of free electrons increases.

In the absence of an externally applied force, the free electrons in copper move at random. When no external force is exerted on copper, its free electrons move around at will. In other words, as shown in Figure 1, the free electrons can go in any direction. Considering that free electrons can move in any direction, there is no net flow of electrons in any given direction.

What happens when an external force forces all the electrons to move in the same direction is depicted in Figure 2. In this case, one end of the copper is subjected to a negative potential while the other end is subjected to a positive potential. This results in a directed flow of charge, with the free electrons all moving in the same direction from negative to positive (electrons). Electric current refers to the directional flow of electrons.

What happens on a larger scale when an external force guides the motion of electrons? Flow (current) of electrons is shown in Figure 3 as being directed from a negative potential to a positive one. The lamp generates light and heat as a result of the current flowing through it. The value of the current (how much it flows through the wires) determines how much heat and light are generated by the bulb.

In mathematical notation, the letter I stands for electric current (For intensity). The rate of charge flow per second is a measure of current intensity. Current strength is proportional to the rate of charge transfer per second.

### Coulombs and Amperes

Single-electron charge fluctuations are insufficient to serve as a useful metric for charge. So, we use C (for Coulomb) as our fundamental charge measurement. One coulomb is equivalent to the charge on 6.25 x 1018 electrons. There is one Ampere (A) of electric current when one coulomb of charge moves past a point in one second. As a result,

By dividing the total charge (in coulombs) by the time (in seconds), we can calculate the total current (in amperes) passing a given point. via Mathematical Formula

Where

I= the intensity of electric current in amperes

Q= the total charge, in coulombs

T= the time it takes the charge to pass a point, in seconds

#### Example 1

Every second, a copper wire transfers three coulombs of charge. Do we know the true worth of electric current?

Solution

Current is calculated using equation 1.

To better illustrate the connection between amperes, coulombs, and seconds, consider Example 1. Since coulombs cannot be measured directly, Equation 1 is not used to determine electric current. You will learn that there are more efficient methods of determining current that you should use instead.

Two Theories: Conventional Current and Electron Flow.

You’ll run into two different explanations for electric current in everyday life.

According to the Standard Current Hypothesis, current is defined as the movement of charge from a positive to a negative terminal. Conventional current theory is the more established of the two approaches to current and was, for a long time, the only one taught anywhere besides technical and military institutions, hence the name.

The Electron Flow Theory is the more recent explanation. Current is defined in terms of the flow of electrons from negative to positive, according to the theory of electron flow.

Figure 4 compares two different explanations for electric current. A battery and lightbulb are included in each separate circuit. In a traditional setup, the positive battery terminal would be the starting point for the current, which would then travel through the lap and back to the battery via the negative terminal. Electrons leave the battery via the negative terminal, travel through the lamp, and then return to the battery via the positive terminal.

It doesn’t matter that both circuits in Figure 4 are carbon copies of each other. It’s all in the terminology used to describe the electric current that separates the two. In actuality, the way you conceptualize current has no bearing on any measurements, tests, or calculations involving circuits. But you should familiarize yourself with both points of view, as they are both used by engineers, technicians, and technical publications. Here, we analyze current using the flow of electrons as our guide. In other words, we’ll pretend like current is just the movement of electrons from negative to positive charges.

### Direct Current (DC) Versus Alternating Current (AC)

Both direct current (DC) and alternating current (AC) are common ways to classify the flow of electricity (AC). Figure 5 shows the distinctions between direct current and alternating current.

The flow of direct current only goes in one direction. The direction of the current flow is consistent. If you hear the term “direct current,” you might assume that the current is always a constant rate. Figure 5a, for instance, depicts a graph in which the current is always 1A. Even though a constant value is assumed, DC can actually fluctuate in price. However, the flow of current remains in the same direction.

Bidirectionality of Alternating Current. That is, the polarity of the current was constantly shifting. Take figure 5b as an example: the graph shows the current first increasing to a maximum in one direction, and then increasing to a maximum in the opposite direction. Keep in mind that the value and direction of the alternating current depicted by the graph are both in constant flux.

### Electric Current Produces Heat

Electricity creates heat wherever it is used, so any device or circuit that uses electricity will generate some degree of temperature. The quantity of heat generated is proportional to the magnitude of the electrical current. Because of this, many devices that use a lot of electricity, like motors, tend to get warm when they are in use. The heat generated by some high-current circuits necessitates the use of cooling mechanisms.

It is not always a bad thing that electricity generates heat. Electricity can be used to generate heat for a variety of appliances and lighting.

### Putting it all together

In a room temperature copper environment, free electrons are produced. When not guided, these free electrons move at random, with no net flow in any given direction.

Forces acting on free electrons will cause them to move in a straight line. Electric current refers to this regulated flow of charge.

The intensity of an electric current is denoted by the letter “I.” An electric current’s strength is proportional to the quantity of charge being transferred and the duration of that transfer.

Amperes are the units of measurement for electric current (A). One ampere of current flows when one coulomb of charge moves past a given point in one second.

Both of these theories are considered viable options at this time. Current is defined as the movement of charge (electrons) from a negative to a positive terminal, according to the electron flow theory. According to the standard current theory, current is defined as the movement of charge from a positive to a negative terminal. These two schools of thought are equally popular. No matter how you define current, your measurements, calculations, and testing of a circuit will always yield the same results.

Both direct current (DC) and alternating current (AC) circuits are present in practically all electrical and electronic systems. The direction of the current is constant and uniform in DC circuits. Current in AC circuits constantly reverses direction.

## Voltage

Simply put, voltage is the driving force behind current (the movement of electrons) in an electrical circuit. Here we will examine voltage and its role in producing current in greater depth.

### Generating Current with a Battery

Figure 7a shows a battery with two prongs. It is because of this preponderance of positive ions that the positive (+) terminal is said to have a positive potential. Since there are more electrons at the negative (-) terminal, its potential is negative.

As a result, there is a potential difference, also known as voltage, between the terminals.

Creating a current by connecting the copper wire and the battery’s positive and negative terminals with the lamp (Figure7b) causes electrons to flow from the negative terminal to the positive. As a result, electrons move in a specific direction, from the battery’s negative (-) terminal to its positive (+) terminal.

There are a number of points worth emphasizing:

1. Voltage, which is a force that propels electrons, is also known as electrical force (E) or electromotive force (EMF) (EMF).
2. Voltage and current are two different things. Electric current is the rate at which electrons move from a negative to a positive terminal. When electricity is produced, current flows as a result of a force known as voltage. A voltage source is required for the occurrence of current (electric force).

Electric potential is measured in volts (V). If you want to get technical, one volt is the amount of electrical force required to move one coulomb (C) of charge using one joule (J) of energy.

1 volt= 1 joule per coulomb
or
1 V=1J/C

## Resistance

There is some resistance to current in all elements. The term “resistance” is used to describe this kind of opposition to the flow of current. When a given voltage is applied to a more resistant element, component, or circuit, less current flows.

Ohms are the unit of measurement for resistance (R). Omega () is the Greek letter used to represent ohms. When one volt of electrical force is applied, one ohm of resistance is enough to limit the current to one ampere. Figure 8 depicts this definition in action.

Figure 8 is a schematic depicting a battery wired to a resistor. An item that provides a fixed amount of resistance is called a resistor. A resistance of 1 restricts the current to 1A at a voltage of 1V, as depicted in the figure. Take note that the battery’s positive terminal is represented by the long end-bar on the schematic symbol, while the negative terminal is represented by the short end-bar.

### Putting It All Together

Definitions of charge, current, voltage, and resistance have been presented. Table 1 provides a handy overview of these electrical characteristics.

Table 1 contains many properties that can be defined in terms of one another. During our resistance lesson, we learned that one ohm is the amount of resistance that restricts current to one amp when one volt of electrical force is applied. In a similar vein, we can reframe the ampere and the volt as follows:

1. The electrical current flowing through a circuit with a resistance of one ohm is measured in amperes.
2. The electrical force necessary to produce a current of one amp through a single
magnitude of an ohm.

## Q&A

### What is voltage?

In a circuit, current is created by the force of voltage.

### What is the mechanism by which voltage causes a current to flow in a conductor?

If you look at the terminals of a voltage source, you’ll notice that there are more electrons (negative charge) at one end than there are ions (positive charge) at the other. We call this a “possible difference.” Affinity between the positive ions at one end and the surplus electrons at the other. As a result, current will flow through any wire that connects the power source’s two ends.

### How many volts does a battery have? To what extent is it defined?

Volts are used to measure electrical potential difference. A voltage of one volt is the electrical force required to accelerate a charge of one coulomb (C) by one joule (J). 1 V = 1 J/C.

### What does a coulomb mean in terms of potential energy and voltage?

The relationship between joules and volts is 1 C = 1 J/V.

### In terms of potential and kinetic energy, how would you characterize a joule?

A joule is defined as 1 volt multiplied by 1 coulomb, or 1 J = 1 V 1 C.

### What exactly is electric current? What variables increase or decrease the voltage of an electrical current?

To put it simply, current is the movement of electrons in a material in a particular direction. An electric current’s strength is proportional to the quantity of charge being transferred and the duration of that transfer.

### Can you tell me the smallest possible electric current?

Electric current is typically measured in amperes. One ampere is equal to one coulomb per second.

### Explore the differences between the conventional current theory and the electron flow theory.

According to the standard definition of current theory, current is the movement of charge in one direction, from positive to negative. The movement of electrons represents a net positive charge flow.

### Can you define resistance?

As the name implies, resistance acts as a barrier to the flow of current.

### How do we define the fundamental measure of resistance?

The Ohm () is the standard SI unit for measuring resistance. When one volt is applied, one ohm of resistance will limit the current to one ampere. 1 Ω = 1 A/V.

### Provide an explanation of the meaning of current, voltage, and resistance in terms of the other two.

For a current of 1 ampere to flow through a resistance of 1 ohm, 1 V is needed. If you apply one volt to one ohm of resistance, you’ll get one ampere (A). For a voltage of 1 V, a resistance of 1 will restrict the flow of current to 1 A.