Let’s talk electricity.
We use electric devices like lights, radios, mobile phones and computers etc. every day. We connect these devices to a socket in the wall or load them with batteries, but what exactly is electricity?
To understand electricity, we first need to examine the atom. Atoms are the basic building blocks of all material around us. They are made up of several smaller particles, including electrons.
Electrons have a negative electric charge and whiz around a positively charged nucleus (made of positively charged protons, and neutrons, which do not carry electric charge) inside atoms. Sometimes these electrons escape and move around between atoms or get captured by a different atom. These escaped electrons are the basis of the electricity we use every day.
Some materials called insulators hold their electrons very tightly. Electrons do not move easily through these materials. Examples of insulators include plastic, wood, cloth, glass, or, indeed, dry air. While electrons typically do not flow easily through insulators, it is still possible to transfer some electrons from one insulator to another. One common way is to rub two of these objects together. This creates an imbalance of positive and negative charges, called static electricity . If you have ever rubbed a balloon against a fabric and then stuck the balloon to a wall, that is an example of static electricity. Hair standing up on a cold winter day is another example of static electricity.
But do you know why the balloon sticks to the wall, or your hair stands on end? This happens because they become electrically charged, and electric charges push and pull on each other. Opposite charges (a positive and a negative) attract, or pull towards each other. By contrast, like charges (two positives or two negatives) repel, or push away from each other. Figure 1, below, shows this interaction between charges.
Figure 1. Like electric charges (two positive charges, as shown, or two negative charges) repel each other, or push each other away, while opposite charges (a positive and a negative charge) attract, or pull toward each other. This figure shows what would happen if you had electrically charged balls hanging from strings. Two like charges push away from each other, and two opposite charges pull toward each other.
Something similar to what is depicted in Figure 1 (left picture) happens when the hairs stand up on your head when taking off a wool hat on a cold winter day. Rubbing of hair against the wool hat electrically charges the hairs, and because all the hairs have “like” electric charges, they repel each other, so the hairs move as far away from each other as possible.
Sometimes, when enough static electricity builds up on an object, it will create a spark. A spark is when electrons jump through the air from one nearby object to another. This is called a static discharge. You may feel a tiny static discharge when you shuffle your feet across a carpet and then touch a metal object like a doorknob. Lightning is an example of a very large (and dangerous!) static discharge.
Point of Interest
An atom that loses one or more electrons has more positive charges than negative charges (electrons). Therefore, it is positively charged. An atom that captures one or more extra electrons obtains a total negative charge. Charged atoms are called ions.
Electric Current
So, charged particles are at the basis of all electricity and static electricity is a phenomenon caused by electric charges at rest.
Certain materials have some loosely held electrons, which can escape from one atom and move around easily between other atoms. We call these electrons free electrons. Materials with a lot of free electrons are called conductors. They conduct electricity well. Most metals are good conductors.+
When a lot of free electrons are all moving in the same direction, we call it an electric current. The amount of electric current refers to the number of electrons or to be precise, their charges, passing through an area per unit of time, and is measured in amps.(Amperes).
Just like water needs a pressure difference to start flowing, electrons require an electric potential difference to make them move. The potential difference provides the energy to create movement. Electric potential difference is also called voltage and it is measured in volts (abbreviated V). In the case of water, pressure can be created by a water pump or difference in height, like a water tower. In electronics, batteries and electric generators are common sources of voltage. The presence of two different charges also creates a voltage; it gives the electric charges the energy to flow.
Conductors allow current to flow through them easily, and charges do not lose much energy as they flow through these materials. Similar to how water gets slowed down when it encounters a smaller section in a pipe, electric current can encounter materials that are harder to get through. This obstruction to flow is quantified by a variable called resistance and measured in ohms (abbreviated Ω). The higher the value of the resistance, the more the material hinders (or resists) the current, and the more energy is lost as current flows through it. The voltage, the current it generates, and the resistance are related; this relationship is now known as Ohm’s law and states that voltage is equal to current times resistance.
The total electric energy provided by a source is the amount of charge times the voltage. A source providing a larger voltage or more charges (more electrons) will both result in delivering more electric energy, which, in turn, allows it to power “heavier” electric devices or appliances.
Point of interest: Direction of Electric Current
Electrons, being small and light, move easily and create the bulk of electric current we encounter, like current received from wall sockets or produced by most batteries. Sometimes, electric current is created by the flow of other charged particles like ions (atoms that have a net electric charge due to a lack or surplus of electrons). To accommodate all variations, electric current is more accurately defined as the amount of electric charge passing per unit of time, regardless of what particles carry the electric charge.
So far, we have only described the amount of current. The direction is given by the sign (positive or negative) of the current. Conventionally, positive electric current is opposite the direction of electron flow. This is called the conventional current. This means that if you draw an arrow in the direction electrons are moving through a wire, the conventional current points in the opposite direction. See Figure 2 below.
Batteries are often used as a source of electric current. A battery has a positive terminal, marked by a “+” symbol, and a negative terminal (although “-” is the symbol for negative, it is usually not printed on the battery). The negative terminal has a surplus of electrons, giving it a net negative charge. These electrons flow from the negative terminal to the positive terminal when there is a conductive path connecting them. The direction of conventional current is opposite this—from the positive terminal to the negative terminal, as shown in Figure 3.
Figure 3. When conductive material connects the two terminals of a battery, electrons will flow from the negative to the positive terminal. The conventional current will point from the positive to the negative terminal.
Point of Interest: Energy Consumed
Most of our appliances specify how much electric energy they require per second they are in use. This is called a power expressed in watts (abbreviated W). Power represents the amount of electric energy (or voltage times charge) consumed by the appliances per second it is running.
Electromagnetism
Electricity and magnetism are very closely related. The study of both, and how they are connected, is called electromagnetism. Below is just a brief introduction to electromagnetism.
One common example of the interaction between electricity and magnetism is an electromagnet. An electromagnet is a special type of temporary magnet that only generates a magnetic field when electric current is flowing and this makes electromagnets very convenient because they can easily be turned on or off, and can create very strong magnetic fields.
A single, straight wire with current flowing through it creates a circular magnetic field configuration, as shown here
This illustration shows the magnetic field around a current-carrying wire. The current (capital letter “I”) is represented by the white arrow. The magnetic field (capital letter “B”) is represented by the red arrows. You can use your right hand, as depicted, to determine the direction of the magnetic field.
The hand in the illustration above represents the right-hand rule, used to predict the direction of the magnetic field created by a current. When you point the thumb on your right hand in the direction of current flow, your fingers curl in the direction of the magnetic field. If the current reverses direction, the magnetic field lines will also reverse direction.
A bigger current will produce a stronger magnetic field. However, even a strong current in a single wire does not make a very strong electromagnet. To make a much stronger electromagnet, you can wrap the wire into a coil, as shown below
When there is no current flowing through a wire coil, there is no magnetic field (top). When electric current flows through the coil, it creates a magnetic field very similar to the field around a bar magnet, represented by the green/red arrow in the coil (middle)). If the direction of the current reverses, the direction of the magnetic field also reverses (bottom).
An electric current is nothing more than moving electric charges. Anytime an electric charge moves, a magnetic field is created. You might wonder if moving magnets (or a changing magnetic field) would create an electric current or get electric charges to move?
What do you think?
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