Nikola Tesla was a Serbian-American electrical engineer and inventor. He is best known for inventing alternating current (AC) which allowed for electricity to be generated and supplied across long distances. He was famously in a feud with American inventor Thomas Edison (who believed DC current was better). Eventually Tesla won and the world now has running electricity because of him. Through the story of Nikola Tesla, we will explore electricity in the home.
Nikola Tesla was born in 1856 in Serbia. In school, Tesla became interested in demonstrations of electricity by his physics professor. He noted that these demonstrations of this “mysterious phenomena” made him want “to know more of this wonderful force”. In 1882, Tesla moved to Paris and began working in what was then a brand new industry, installing indoor incandescent lighting citywide in the form of an electric power utility. There he gained a great deal of practical experience in electrical engineering. Management took notice of his advanced knowledge in engineering and physics and soon had him designing and building improved versions of electricity generating dynamos and electric motors. In 1887, Tesla developed an induction motor that ran on alternating current (AC), a power system format that was rapidly expanding in Europe and the United States because of its advantages in long-distance, high-voltage transmission. This was a revolutionary invention that changed the world. This angered his once mentor, now rival, Thomas Edison. Edison wanted to show that DC electricity was better than AC; he even went so far as to electrocute an elephant live on stage to falsely claim that AC current was dangerous. This battle lasted a few years but eventually the world recognised the brilliance of Tesla’s AC current. Tesla would go on to invent many more technologies and is widely accepted as one of the greatest minds in the history of electrical physics. His invention of alternating current allowed for electricity to be brought into people homes, and changed our lives and society forever.
Electricity in the Home
Have the lights ever gone out in your house? Or have the plugs in one room ever just stopped working? This is generally due to a fuse ‘blowing’ or a circuit-breaker ‘tripping’ in the electrical circuit within your house. Have you ever wondered why the plugs stop working in just one room, and not throughout the whole house? Or how, when one lightbulb blows, the other bulbs continue to work? This ‘behaviour’ arises because in every home there is something called a ring circuit. A ring circuit comprises parallel circuits for lighting and other connections. A typical ring circuit has the following:
- Live and neutral wires carrying electric current;
- Earth wire for safely earthing the appliance (so you don’t get electrocuted!);
- Fuses (in your plugs);
- Circuit Breakers;
- Sockets as points to connect to the electric current.
Because electric current can give you a nasty shock, your home is filled with safety features that protect you when you use any electrical appliance.
A fuse is a safety feature installed in plugs. It consists of a thin metal wire that heats up when electricity is passed through it. If the current going through it is too high, the fuse will melt and stop the flow of electricity. Different fuses have different ratings like 1 A, 2 A or 5 A – this indicates how much current it can ‘tolerate’, i.e. can flow through it, without it blowing. When a plug fuse blows in an appliance, the appliance will not work again unless you replace the blown fuse with a new one.
The plugs which are connected to every appliance in your home all contain the following:
- A brown wire, called the live wire. This wire is connected to the fuse in the plug and carries the electric current to the appliance.
- A blue wire, called the neutral wire. This is connected to the left of the plug and carries current back from the appliance.
- A yellow and green wire, called the earth wire. This is connected to the metal casing of the appliance and runs to the ground to earth the appliance.
Most modern houses will have circuit breakers instead of fuses on their ring circuits. This is because when a circuit breaker trips, it can be reset by simply flicking a switch. However, it’s important to remember that a blown fuse or tripped circuit breaker generally indicates misuse of an appliance or a faulty appliance. One should try to eliminate the fault before replacing a fuse or before resetting a trip switch.
How much does electricity in our homes cost, and how do we measure it?
Nothing comes for free in this life, including electricity. The electricity in our homes has to be generated and transported by lines to get to your home, and this all costs money. So the electricity companies need a way to charge for the use of electricity. For this, they use a unit called the kilowatt-hour (kW h). The watt (W) is the unit for power, so 1 kW = 1000 W. The kilowatt-hour unit takes into account the amount of power being used by an appliance as well as the time over which it uses that power. For example, if your toaster operates at 4 kW, and you leave it running for 2 hours, you’ll have consumed 8 kW h of electricity. Electricity companies charge a certain rate per kilowatt-hour (e.g. € 0.20 for 1 kW h). So for the example above, the cost of running your toaster for 2 hours would be 0.20 x 8 = € 1.60.
AC/DC: Alternating Current and Direct Current
You may be asking, what does this all have to do with Nikola Tesla? All of the ‘mains’ electricity flowing in your home is in the form of alternating current (AC). There are two types of current; direct current (DC) and alternating current (AC). DC current travels around a circuit in just one direction, from the negative terminal of a battery to the positive terminal. AC current changes direction 100 times a second as it travels around the circuit. AC is used to power the world because it is so much cheaper and easier to transport or transmit than DC current. The biggest difference between AC and DC is that transmission wires carrying AC current will transmit power with much lower losses than DC current at the same power level: in effect AC transmission lines will not heat up as much as DC ones would carrying the same electrical power. The heating up of electricity carrying wires ‘consumes’ some of the electrical energy being transmitted. This energy is lost to the environment, and reduces the efficiency of the transmission system. This is why DC current was never a viable option for large scale electricity generation and transport and why AC current won, and allowed us have an efficient transmission network which can reach the most remote parts of the country.