10th April 2011 The Hall Effect - Magnetism & Electricity

When a magnetic field is applied to a current running through a wire, the current moves either up or down depending on the direction of current and magnet. Even through a piece of metal, the magnetic field still affects the beam.

As the negative charge moves up, there is a positive charge moving down to balance it.  Once the top and bottom are 'full' the rest of the particles carry on as before since they are attracted by the positive bottom part which balances the magnetic field.

Since there are negative charges at the top, and positive at the bottom, there is voltage across the wire. This can be measured. The Hall effect is the voltage across divided by the current through, which is a resistance.

Measuring this charge is how burglar alarms on a door work. They have a magnet one side and a detector the other side which measures the change in magnetic field.

http://www.sixtysymbols.com/videos/halleffect.htm

8th April 2011 Electricity Meters

It is illegal to remove the tamper tags on an electricity meter.  Each tag is stamped with the number of the engineer who fitted it.  If the engineer loses their tagging machine, they have to report it to the police.

Sometimes electricians remove the tags to isolate the current so they can work safely on the fusebox.  They should not do this, but instead the meter installers should be called and asked to fit an isolating switch.

5th April 2011 Linking up Nature with Electricity

Electricity

1784 Charles-Augustin de Coulomb quantified the force between electrical charges, discovering the inverse square law that is now known as Coulomb’s law.

Electricity and Nature

1750s Benjamin Franklin postulated and demonstrated that lightning is a form of electricity with his invention of the lightning rod and a particularly infamous kite flight.

1791 Luigi Galvani discovered that the muscles of dead frogs could be excited by electrical sparks.

Electricity and Chemistry

1800 Italian physicist Alessandro Volta developed the first chemical battery, known as the voltaic pile.

Electricity and Magnetism

1820 Danish physicist Hans Christian Oersted observed the twitch of a compass needle in the presence of an electric current which was an experiment he performed for the first time in a lecture!

Benjamin Franklin had magnetised needles by discharging electricity through them
Sailors reported the reversal of polarity of compass needles after their ships were struck by lightning.

1831 Michael Faraday showed that a changing magnetic field could produce an electric field.

James Clerk Maxwell completed the fundamental theory of electromagnetism, and the realised that light is an electromagnetic wave.

Electromagnetism

If a compass is put to the east or west of a north pointing wire (with current flowing south to north), it will point to the NW. When above, it will also point NW, but when below, it points NE. Why is this? It's is because the magnetic field spirals around the wire according to the right hand rule. The angle of this deviation is affected by the size of the current. The angle would be larger if it were not for the effect of the earth's magnetic field. This works in the same way as the field around the wire, if you imagine a wire stretching from the South Pole to North.

[Source: The Birth of Electromagnetism-1820]