Electricity Basics and Explanation of Shock
Lessen for Everybody
Forward: In this article I explain electricity and how it shocks a human.
By: Chrysanthus Date Published: 1 Sep 2012
Introduction
Current
Current is the flow of tiny particles (cannot be seen) in a material from one point to another. These particles are called electrons. You cannot see them, but the effects of current can be felt; for example in lighting, moving machine parts, transmitting and displaying of TV signals.
Conductor
The allowance of electron flow in a material is the conduction of electricity. It is not every material that can conduct (allow flow of electrons) electricity. Some materials are good conductors of electricity and others are poor conductors, while some are in-between. Many metals are good conductors of electricity. Almost all the wires that you see around you that carry current are of the metal, copper.
Flow of Current
Current always flows round through a loop. If current starts at one point, it must go through a loop and come back to that point. The speed is so fast that you cannot notice it. Because current must flow in a loop, that is why you always have 2 wires to transmit current (see below). In some cases called the DC (direct current) cases, one of the wires is referred to as the forward (or positive) wire and the other is called the return (or negative) wire.
Imagine a pair of wires on a board from the left of the board to the right of the board. Assume that the forward (or positive) wire is higher up and the return (or negative) wire is lower down. Also assume that the 2 wires are close together but not touching.
Imagine that at the left end of the pair of wires you have a battery connected to the two terminals. Also imagine that at the right end of the wires, you have a bulb connected to the 2 terminals. As soon as current starts at the top end of the forward wire it flows extremely fast to the right, through the bulb and back through the return wire, through battery and to were it started – that is a loop. It is the current flow through the bulb that makes the bulb to light. If the current flow in the loop is continuous, the bulb continuous to light.
Note: even though we say current flows from the positive (top) terminal of the battery round the loop to the negative (bottom) terminal of the battery, electrons actually flow in the opposite direction.
Do you want the bulb to continue lighting forever? It should not light during the day. So you need a switch to allow current flow and stop current flow. A switch has 2 important states: it can be open or close. When it is open (physically) current cannot pass through it. When it is close (physically) current can pass through it. So you can break one of the 2 wires of the electrical system above and insert a switch. When you want the bulb to light, you close the switch and so current flows. When you do not want the bulb to light, you open the switch and so current stops flowing through the loop. Conventionally the switch is inserted in the forward (positive) wire.
Voltage Source and Load
The battery is an example of what is called the voltage source. There are other forms of voltage source that will push current through a loop. The bulb is an example of what is called the load. There are other forms of load that consume power from the voltage source. The wires transmit the power through current flow. The TV set, for example, is an example of a load to the current from the wall socket of your house. However, the current from your wall is an example of what is called AC current (see later).
A voltage is the force from the voltage source (battery) that pushes current round the loop. The current loop (battery, 2 wires and bulb) is called a circuit.
Current and Voltage Measurement Units
Current is measured in Amperes abbreviated, A. That is, the unit to measure current is, A. Voltage is measured in Volts abbreviated, V. That is, the unit to measure voltage is, V.
As said above, for current to flow, it must go through a loop. In many cases the return wire in a circuit is connected to the grown (earth by your house). In these cases the grown and the return wire are said to be at the same voltage potential. For practical purposes, all the points of a wire are said to be at the same voltage potential. Know that grown outside your house and the floor of your house are effectively the same thing from an electrical point of view (see below).
Now, current will always move from a higher potential to a lower potential. In the isolated circuit (above), current moves from the forward (positive) wire, through the bulb and to the return wire (negative wire). The forward wire is at a higher potential compared to the return wire. Anything that is touching the forward bare wire is at the same potential as the forward wire and current will flow through it as well as the forward wire. Usually nothing is allowed to touch the forward bare wire. Anything that is touching or connected to the return bare wire (e.g. the earth) is at the same potential as the return wire and current will flow through it as well as the return wire.
Remember, I have said above that current will always flow from a higher potential to a lower potential. If 2 things (such as return wire and earth) connected (touching) are at the same potential they share the current flow at that potential.
Now, if a human is bare footed and he touches the forward bare wire, while the return wire is connected to the earth, current will flow from the forward wire through the human, to the ground. That current flow through the human is shock. If the current is too high, the human will die. Now, the higher the voltage the more the current. Higher voltage means more driving force of current.
The shock current loop is as follows: Current moves from the voltage source through the top wire until it reaches the hand of the human. Form there it goes through the human to the ground. From the ground it goes to the return wire and back to the voltage source. This current flow is extremely fast. For the duration that the human is having the shock, there are 2 current loops: one moves from the top of the voltage source through the top wire, through the human, through the bottom wire and back to the voltage source; the other loop current moves from the top of the voltage source through the top wire, all the way to the bulb, through the bulb to the bottom wire, and through the bottom wire back to the voltage source.
You might have heard that some people have shock and they die. This depends on how strong the shock is. The greater the strength, the more the likelihood of death! The strength of shock depends on the duration of the shock and/or size of the current and/or the size of the voltage from the voltage source. The more the duration and/or the higher the value of the current and/or the higher the value of the voltage, the more the shock is deadly.
The power from the socket of the wall in your house, may not kill an adult, but may kill a child. As the child grows older to become an adult, the level of electrical power the child can withstand increases. Of course there is a limit. At a certain level of electrical power (current and or voltage), is death to all humans: child or adult.
Warning: whether you are a child or an adult, never touch any bare wire carrying current: it is difficult to tell, when the shock is deadly.
Insulators
Above I said that there are good conductors of electricity and poor conductors of electricity. There are certain materials that will allow current to flow through them and others that will not allow current to flow through them. The ones that allow current to flow through them are good conductors of electricity. The ones that do not allow current to flow through them are poor conductors of electricity.
If your are bare footed and you hold one end of a dry stick or one end of a piece of plastic, then you let the other end touch the bare wire of the forward cable while the return cable is earthed, you will not have a shock. This is because the dry stick or the plastic is a poor conductor of electricity and so current does not pass through it to shock you. Shock means current passes through your body.
If you go to an electrical shop to buy a cable to wire your house you will notice that the cable is surrounded by plastic. That plastic is an insulator. An insulator is a poor conductor of electricity. Since it is a poor conductor of electricity, it prevents current from passing through it. Wires of cables are always covered with insulators. This is so that if current is passing through the wire and if somebody touches the cable the person will not have a shock.
Any flexible metal wire (usually of copper) that can allow current to flow through it (very well), is a conductor (of electricity). A cable is a conductor surrounded by an insulator. More than one cable in the form of a wire is still a cable. A cable or conductor is a wire.
Resistance
Every material would conduct electricity. Some are good conductors while others are poor conductors. Others are somewhere in the middle. The poor conductors do conduct but they conduct very little and so their effects of conduction (allowing current through them) are negligible and usually ignored (and does not lead to shock).
The resistance of a material is the capacity of the material to resist current flow through itself. Poor conductors are good resistance of current while good conductors are poor resistance of current. So, conductance is the opposite of resistance.
Size of Material
The bigger the material in size (quantity) the lower (less) the resistance! So a small material may resist current preventing shock, but when you increase the size it allows current (and results in shock if it were between a live conductor and somebody). With some materials you have to increase the size too much before it would allow current. With others, a bit of increase allows noticeable current.
Why the Floor and the Ground Allow Current
The floor of the house has a lot of cement and sand. If you take a bit of your floor or a bit of the earth outside your house to the laboratory and try to pass current through it, you will notice that its conduction of electricity is small, meaning it presents a high resistance. However, since the floor of a house joined (connected) to the ground outside the house is big, meaning its size is big, so the resistance of floor and ground combined, is low, making it a good conductor of electricity. This explains why if you are bare footed on the floor or on the ground, and you touch a live bare wire (carrying current) you will have a shock. In this case, current leaves the wire, passes through your body, to the floor or ground and back to the voltage source. The current loop must always be completed; in some cases it is difficult to know where the voltage source is; however the good electricians will always know where the voltage source is.
Note: water normally is not a conductor of electricity, however, when you pass current through it, the water reacts and conducts electricity. So, consider water as a good conductor of electricity, and keep it away from electrical circuits.
Direct Current
Direct current abbreviated, DC is current of the classical circuit I described above. In the circuit, current flows steadily in one direction, from the positive terminal of the battery through the forward conductor (wire) through the load (lamp) back through the return conductor and to the negative terminal of the battery (voltage source). Remember, the flow of current is very fast.
Note: the two terminals of the battery are not the same. One is labeled as the positive terminal and the other is labeled as the negative terminal.
Direct Current is the flow of current of the same amount (say 2A), in one direction continuously, for a long time.
In this article I have explained the basics of electricity and how electric shock occurs using DC circuit. In the next article titled something like, Alternating Current Basics and Explanation of Shock, I explain a similar thing but with a slightly different type of current.