Current electricity

The Discovery of current and therefore electricity has transformed our lives. We cannot think of our lives without it. None of the electronic devices, vehicles, planes, medical equipment, and the likes would have existed without the discovery of charge and understating how it works. Therefore, it is important that learn about it.

Charge

To understand current, first, we have to look at the atoms itself. Essentially, everything that is around us, the plants, rocks, earth, sun, moon, and even you and me, is made up of tiny particles called atoms. We can say that we are a bag of atoms.

Atoms itself are made up of three subatomic particles, namely; electron, proton, and neutron.

In an atom, a proton (which is a positively charged particle) and a neutron (which does not possess any charge) hold the central position. They are held together by a strong nuclear force, meaning, it is very difficult to break their bond under normal conditions. However, electrons (particles that are negatively charged) on the other hand, occupy space around the nucleus. The free/valance electrons (electrons in the outermost shell) of a good conductor like copper and aluminum are always ready to move to nearby atoms.

Remember, it is only electrons that can move and not protons or neutrons. In solids, movement of free electrons carries current while in liquid and gases, both positively and negatively charged ions carry current. Only conductors possess free electrons.

Let us quickly take a look at the atomic structure of Aluminum

The atomic number of aluminum is 13. This means it has 13 electrons and 13 protons (represented as 13P in the figure). Following the octet rule for electron distribution in an atom, aluminum has 3 free/valance electrons.

There are four important generalizations that we can make from above:

1.      Aluminum is conductor because its atom has free electrons (each atom has three electrons ready to move to nearby atoms).

Generalization:

In general, all conductors have free electrons. 

2.      Aluminum is electrically neutral because the total number of negatively charged electrons and positively charged protons are equal.

Generalization:

In general, though all things are made of charges, most of the time positive and negative charges are balanced in an object. 

3.      If aluminum atoms lose just one electron to any material in contact, it will become positively charged, because, in the aluminum, the total number of protons will be more than the total number of electrons. They will retain this charge imbalance (be positively charged). This kind of stationary charge is called static electricity.

The charge imbalance in a material can be both positive and negative.

Generalization:

Some materials can retain charges and can be either positively charged or negatively charged.

1.      The opposite of static electricity is current electricity - which charges move. For charges to move, we need a device like batteries, generators to do the work. The amount of work required to perform in carrying a charge from one point to another is called the potential difference.

Generalization:

Charges in a conductor cannot move without a potential difference at its two ends.

Potential Difference

Devices like batteries or generator (or sometimes referred to as mains supply) help create a potential difference at the two ends/terminals of a conductor.

Here is how it works:

The two sides of the battery have different concentrations of electrons. The region with a high concentration of electrons (marked with negative sign) is called the region of low potential and the region with a low concentration of electron or deficit of electrons (marked with a positive sign) is called the region of high potential.

When a conductor is connected to a device like a battery, as shown above, battery creates a potential difference at the two ends of a conductor. The difference in the potential energies makes electrons move from the negative terminal (region of high potential) to the positive terminal (region of low potential). Though electrons or charge carriers flow from the negative terminal to the positive terminal, the flow of current is represented from the positive terminal (region of high potential) to the negative terminal (region of low potential). This is called the conventional (meaning it is widely accepted) direction of the current.

The flow of electrons in a circuit is analogous to the flow of water. Water always flows from higher height to lower ground and the flow continues until there is a difference between the heights. Similarly, electrons will continue to flow as long as there is a difference between potentials at the two ends of the conductor. The potential difference is also known as voltage. The amount of work done in moving a unit charge from one point to another is called potential difference (p.d.).

Voltage is measure in volts (V). A device called voltmeter measures it.

The conductor used by the electrons as a path to travel is called a circuit.

There are two types of potential differences:

1.      The potential difference of a cell when the circuit is open (ends of a cell are not connected) is called electromotive force or emf.

2.      The potential difference of a cell when the circuit is closed (both ends of a cell are connected with a conductor) is called terminal voltage.

Electric Current

Electric current is the measure of how much charges (or electrons) pass across any cross-section of a conductor in a certain given time. 

Therefore;

Electric current (I) =(Charge (Q))/(Time (t))

Or;

I =Q/t

The current is measured in Amperes (A) and the charge is measured in coulombs (c). It is measure by an instrument of Ammeter.

Electrical Resistance

When a conducting wire is connected to a battery as shown in the figure below, we know that due to the difference in the potential, the electrons will flow from negative terminal to the positive terminal of the battery.

The word ‘flow’ here is used lightly. In fact, electrons do not really flow. What happens here is, when the circuit is closed, the electrons present in the negative terminal of the battery will knock out or push the nearby free electrons of the atoms in the conductor. Then these free electrons will, in turn, knock out the free electrons of the nearby atoms and this process will continue until free electrons of the atoms near to the positive terminal are knock into it. When this happens, it looks as if electrons are flowing.

However, the ‘flow’ is never smooth. When the electrons are knocked out of their atoms in the conductor, they collide with each other giving rise to the resistance. The obstruction offered to the flow of electric current by the material of the conductor is known as electrical resistance.

Resistance is measured in Ohms ( ) by a device called Ohm-meter.

The resistance of a wire depends upon:

1.      nature of the material of the conductor,

2.      length of the conductor,

3.      the thickness of the conductor, and

4.      the temperature of the conductor.

Common Sources of Electricity

Electricity is generated from various sources. Some of the sources are:

1.  Solar (Sun) Energy

2.  Hydro – Electricity

3.  Wind Energy

4.  Fossil Fuels – Diesel, Petrol, Natural gas, Coal, etc.

5.  Nuclear Energy

Distribution of Electricity

The electricity generated in power plants is distributed across the community or a country using a grid system.

In a grid system, before the distribution of electricity, it first goes to the substation located near to the power generation plant where it is converted to a higher voltage using step-up transformers. This is done so that the electricity can travel long distances.

When it reaches to its consumers, the voltage is decreased depending upon types of consumers using step-down transformers. The following figure represents how the grid system works.