Science in Action Notes: Electrical Principles & Tech. (1.0) | Print |
Research Links:

'The Atoms Family' (A Great Electrical Resource Site)
'Just for Kids' (Fun and Games - About Electricity)
'Theatre of Electricity'

1.1. - Static Electricity
When you get a 'shock',feel a 'jolt' or a 'spark', you are experiencing the same type of electrical effect that makes lightning. Static electricity happens when there is an imbalance of electrons (which have negative charges).

Electrical Charge

Most objects have the same number of positive (proton) and negative (electron) charges. This makes them neutral (no charge). When there is a difference in the electrical charge, certain actions are predictable, because of The Laws of Electrical Charges.

Charge separation occurs, when a charged object is brought close to a neutral object. The charged electrons repel the electrons in the neutral object and the charged object is then attracted to the protons of the neutral object (balloon on a wall)

Electrical Discharge
is the movement of charges whenever an imbalance of charges occurs. The action results in neutralizing the objects. The over-charged electrons repel the electrons in the object and the positive protons attract the charged electrons causing a discharge or 'miniature lightning bolt'.

Van de Graaff (VDG) Generators
These generators build up an excess of static charge using friction. A rubber belt rubs a piece of metal abd transfers the charge to a sphere. When you touch the sphere the charge builds up on you. (Remember! - like charges repel - that is why your hair strands separate as you touch the sphere as the charge builds up on your body.)

1.2. - Current Electricity
Certain animals, namely, the electric eel, can produce electric shock, to kill or stun prey. They have a special organ that contains specialized muscle cells called electroplaques. Each cell procuces a small amount of electrcity. When all the cells work together, a large amount of electricity is produce and used to help the eel survive. This type of electricity is like static electricity, which builds up and then discharges. It does not flow continuously.

Electrical devices need a steady flow of electricity. The steady flow of charged particles is called electrical current. The flow continues until the energy source is used up, or disconnected.

The rate at which an electrical current flows is measured in amperes (A). This flow varies from a fraction of an ampere to many thousands of amperes, depending on the device. To allow the flow of electrical charges from where they are produced to where they are needed to be used, conductors are used. These conductors are materials (often wires) which allow the flow of electrical charges easily.

A circuit is a pathway that allows the flow of elctricity. Most electrical circuits use wires (as conductors), although others may use gases, other fluids or materials. A circuit consists of a conductor, an energy source, a load and often a switch (to control the flow).

Electrical Energy and Voltage
Electrical energy is the energy carried by charged particles. Voltage is a measure of how much electrical energy each charged particle carries. The higher the energy of each charged particle, the greater the potential energy. Also called 'potential difference', the energy delived by a flow of charged particles is equal to the voltage times the number of particles. Voltage units are volts (V), and for safety purposes, the voltage of most everday devices we commonly use is relatively low, while industries and transmission lines is relatively high.

Measuring Voltage
The simplest way to measure voltage is with a voltmeter.

[red to positve (+) and black to negative (-)]

Some voltmeters can measure a wide range of voltages. These multimeters should be used with caution, so that the sensitive needle is not damaged (by testing a low range with high voltage).

Measuring Voltage with Computers
A voltmeter can be hooked up to a omputer. Hook-up the red and black lead in the same way as you would for a voltmeter.

1.3. - Electrical Safety
Coming in contact with a power transmission line can prove to be deadly. By touching it, a short circuit can occur, beacuse the electricity is trying to find a path to the ground - you can complete the circuit, but it may be fatal.

The Dangers of Electrical Shock
High voltage power lines carry 50,000V of electricity. However, amperage is more important to consider. 0.001A will likely not be felt at all, 0.015A to 0.020A will cause a painful shock and loss of muscle control (which means you will not be able to let go of the line). Current as low as 0.1A can be fatal. Electrical Dangers vary, depending on the situation. When the current can flow easily, it is more dangerous. Insulators (such as wood, rubber and air) hamper the flow of electricity. Moisture is a good conductor of electricity, so avoid water when working with electricity.

Protecting Yourself From Electrical Shock

The Canadian Standards Council issues labels to identify the amount of voltage required to operate electrical devices and the maximum current they use.
Electrical Safety Pointers ...

  • Never handle electrical devices if you are wet or near water
  • Don't use devices that have a frayed or exposed power cord
  • Always unplug an electrical device before disassembling it
  • Don't put anything into an elecrical outlet - except a proper plug for an electrical device
  • Don't overload an electrical circuit, by trying to operate too many devices at once
  • Avoid power lines
  • Don't bypass safety precautions when you are in a hurry
  • Pull on the plug, not the wire
  • Never remove the third prong from a 3 prong plug

Plugs, Fuses and Breakers
The third prong of a 3 prong plug is a ground wire, connected to the ground wire of the building, in case of a short circuit.

Fuses () and circuit breakers () interrupt a circuit when there is too much current flowing through it.

Fuses contain a thin piece of metal, that is designed to melt if the current is too high. Circuit breakers, on the other hand, trips a spring mechanism, which shuts off the flow of electricity through the circuit, when there is too much current. It can be resused over and over (provided the cause of the increased flow is corrected).

The Danger of Lightning
A lightning strike can have 30,000A - more than enough to kill you. Avoid being the target of a lightning strike, by staying low to the ground (horizon) and away from trees. Lightning can also do a lot of damage to a building. Metal lightning rods, that are connected to the ground with a grounding wire are fixed on the roof of many buildings to prevent damage to the building during an electrical storm.

1.4. - Cells and Batteries
An electrochemical cell supplies a steady current. It is a collection of chemicals designed to produce small amounts of electricity. The electricity comes from chemical reactions within the cell. The tiny cells in a pacemaker can last from 5-12 years

Dry Cells
The electricity-producing cells, that are referred to as 'batteries', are called dry cells. They are 'dry' because the chemicals used are in a paste.

The chemical reaction in a cell releases free electrons, which travel from the negative terminal of the cell, through the device which uses the electricity, and back to the positive terminal of the cell. The dry cell is made up of two different metals, called electrodes in an electrolyte. An electrolyte is a paste or liquid that conducts electricity because it contains chemicals that form ions. An ion is an atom or group of atoms that has become electrically charged through the loss or gain of electrons from one atom to another. The electrolyte reacts with the electrodes, making one electrode positve and the other negative. These electrodes are connected to the terminals.

Wet Cells
Wet cells are 'wet' because the electrolyte is a liquid (usually an acid). Each electrode (zinc and copper) reacts differently in the electrolyte. The acidic electrolyte eats away the zinc electrode, leaving behind electrons that give it a negative charge. The copper electrode is positive, but it is not eaten away. Electrons travel from the negative terminal (attached to the zinc electrode) through the device and on to the positive termainal (attached to the copper electrode).

A Car battery, like the one below is made up of wet cells.

A car battery is made up of 6 lead-acid wet cells. Each cell contains alternating positive and negative metal plated (electrodes) in a sulfuric acid electrolyte.

Rechargable Cells
The dry cells and wet cells are called primary cells. The chemical reactions which produced the electricity, cannot be reversed. The chemical reactions in a rechargeable battery however can be reversed by using an external electrical source to rejuvenate the cell. The reversed flow of electrons restores the reactants in the cell. Rechargeable cells are secondary cells, because they store electricity that is supplied by an external source. The most common reactions that are efficient enough to be used for these types of cells are Nickel Oxide and Cadmium (Ni-Cad). The reactants are restored, but the electrodes wear out over time.

Connecting cells together creates a battery, which is a sealed case with only two terminals.

Allesandro Volta made the first practical battery around 1800, by piling zinc and copper plates on top of each other, separating them with electrolyte-soaked paper discs. Humphrey Davy filled an entire room with 2000 cells to make one massive battery. His work led to a whole new field of science called electrochemistry, the study of chemical reactions involving electricity.

Smaller batteries were used to split molecules into their elements, a process called electrolysis.

Many industries use electrolysis to separate useful elements from solutions.

  • Chlorine to make dring water safe.
  • Fuel for the Space Shuttle (to get pure oxygen and hydrogen

Silver and Gold plating can make jewelry and other attractive items look very expensive. The thin coating (which is usually stronger than the original element) is produced through a process called electroplating. This process is often used to protect the metal from corrosion.

Other Electrochemical Applications
Anodizing and Electrorefining are other examples of electrochemical process used in Canada. Anodizing is a process that coats aluminum parts with a layer of aluminum oxide, which is much harder than aluminum. It is used in products such as screen doors, airplanes, car parts, kitchenware and jewellery. Electrorefining is used to remove impurities from metal. Another process used by automobile companies bonds special paints onto car parts.