Difference Between Current and Voltage

Key Difference – Current vs Voltage

In an electric field, electric charges are affected by a force acting on them; thus, work has to be done on a charged particle to move from one point in an electric field to another point. This work is defined as the electric potential difference between those two points. Electric potential difference is also called as Voltage between two points. A movement or a flow of electric charges under the effect of the potential difference is known as an electric current. The key difference between current and voltage is that a current always involves a movement of electric charges under an electric field whereas voltage does not involve a flow of charges. A voltage occurs only due to the existence of an unbalanced charge.

CONTENTS
1. Overview and Key Difference
2. What is Voltage
3. What is Current
4. Side by Side Comparison – Current vs Voltage
5. Summary

What is Voltage?

Since an atom has the same number of protons and electrons, all stable matter in the universe is electrically balanced. However, positively or negatively charged particles may have more or fewer electrons than protons due to external physical and chemical effects. Under a gathering of similar charges, there arises an electric field giving electric potential or a voltage to every point around it. Voltage can be treated as the most fundamental property in electricity. It is measured in volts (V) using a voltmeter.

The electric potential at a point is always considered as a difference between two points, or at a particular point, voltage is regarded with respective to the infinity where the potential is zero. In the point of view of electrical circuit, the earth is regarded as a zero-potential point; hence, the voltage at each point on the circuit is measured with respect to the earth (or ground).

A voltage may be produced as a result of many natural or forced phenomena. Lightning is an example of voltage due to natural occurrence; hundreds of millions of a voltage occurs in a cloud due to friction. In a very small scale, a battery produces a voltage by a chemical reaction, accumulating charged ions in the positive (Anode) and the negative (Cathode) terminals. Photovoltaic cells included in solar panels generate a voltage as a result of electron release from the semiconductor material absorbing the sunlight. A similar effect can be seen in photodiodes used in cameras to detect ambient light level.

What is a Current?

A current is a flow of something, such as the sea water or atmospheric air. In an electrical context, a flow of electric charges, most commonly a flow of electrons through a conductor, is known as an electric current. Current is measured in amperes (A) with an ammeter. Ampere is defined as coulombs per second and is proportional to the voltage difference between two points where the current is flowing.

As shown in figure 01, when the current is passing through a pure resistance R, the voltage to current ratio is equal to R. This is introduced in Ohm’s Law which is given as:

V = I x R

If the voltage dV is changing across a coil, also known as an inductor, a current dI through the coil changes according to:

dI = 1/L∫dV dt

Here, L is the inductance of the coil. This happens since the coil is resistant to the change of voltage across it and produces a counter-voltage.

In the case of a capacitor, the change of the current across it dI is as follows:

dI = C (dV/dt)

Here, C is the capacitance. This is due to the discharging and charging of the capacitor according to the voltage variation.

When a conductor is moving across a magnetic field, a current and subsequently a voltage is produced across the conductor according to Fleming’s right-hand rule.

This is the basis of the electric generator in which a series of conductors rapidly rotates across a magnetic field. As explained in the previous section, accumulation of charges makes a voltage in a battery. When a wire connects the two terminals, a current starts to flow along the wire, that is, electrons in the wire move due to the voltage difference between the terminals. Larger the resistance of the wire, the larger the current is and the faster the battery drains out. Similarly, a higher power consuming load draws a higher current from the supply. For instance, a 100W lamp connected to a 230V supply, the current it draws can be calculated as:

P = V ×I
I = 100W ÷230 V
I = 0.434 A

Here, when the power is higher, consuming current will be high.

What is the difference between Voltage and Current?

Summary – Voltage vs Current

In an electric field, the potential difference between any two points is called as voltage difference. There should always be a voltage difference to generate a current. In a voltage source like a photocell or a battery, a voltage occurs due to the accumulation of charges at the terminals. If these terminals are connected with a wire, a current begins to flow due to the voltage difference between the terminals. According to the Ohm’s Law, the current in a conductor proportionally changes with the voltage. Although current and voltage are interconnected by the resistance, current cannot exist without a voltage. This is the difference between current and voltage.

Reference:
1. Lightning. (2017, May 26). Retrieved May 29, 2017, from https://en.wikipedia.org/wiki/Lightning
2. Photovoltaic effect. (2017, March 23). Retrieved May 29, 2017, from https://en.wikipedia.org/wiki/Photovoltaic_effect
3. The Automation Store. (n.d.). Retrieved May 29, 2017, from https://www.theautomationstore.com/using-a-multimeter-voltmeter-ammeter-and-an-ohmmeter
4. Fleming’s right-hand rule. (2017, February 14). Retrieved May 29, 2017, from https://en.wikipedia.org/wiki/Fleming%27s_right-hand_rule

Image Courtesy:
1. “OhmsLaw” By Waveguide2 (talk) (Transferred byNk/Originally uploaded by Waveguide2) -( Public Domain) via Commons Wikimedia
2. “RightHandOutline” By Douglas Morrison DougM – en.wiki (CC BY-SA 3.0) via Commons Wikimedia