Electrical Effects

As we put a voltage across a circuit, we encourage charge carriers (in a metal the charge carriers are electrons) to travel towards the positive terminal. This creates a current a flow of charge. We are usually going to be talking about a vast quanitity of electrons. These electrons will be moving and thus will have kinetic energy. Quite commonly these electrons will collide with a big massive nucleus of one of the metal atoms. When this happens the electron will have to give up its kinetic energy, this energy will be released on a macro (large external view) as heat. This entire process is known a Joule Heating, it is usual to want to avoid this, unless you are building a heater.

Heating: W = I2Rt

http://resources.schoolscience.co.uk/CDA/16plus/copelech2pg4.html

Joules Law

Chemical: an electric current can cause a chemical reaction.

Electrolysis, Copper Sulfate solution with copper electrodes. Copper ions transfer from the anode to the cathode.

Magnetic effect of an electric current.

Demonstration of effect.

Run a current through a circuit and have a compass or 2 near the wires

Direct electric motor by wally again

Appropriate calculations.

Demonstration of effect.

Demonstration of effect.

Power is

V=EQ

E=VQ

Qt=VQt=VI

Et=P=VQt=VQt=VI

http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway/living_future/3_fuels_for_power1.shtml

Everyday examples.

Electric efficiency

http://resources.schoolscience.co.uk/CDA/16plus/copelech1pg1.html


Apart from superconductors, silver is the best conductor of electricity, followed by copper (95% of the conductivity of silver), gold (69%) and aluminium (60%). If 1 kg of silver were made into a wire 1 km in length its resistance would be 168 Ω. If the same were done with 1 kg of copper the resistance would be 150 Ω. For gold and aluminium the resistances would be 440 Ω and 72 Ω respectively. The reason for this is that the area of cross section of the aluminium wire would be much greater than all the others because of its low density; this would give it the lowest resistance (and best conductivity) per unit mass. Aluminium is also the best choice in terms of cost. However, in practice an alloy of aluminium is used in transmission lines to give it greater strength, although that increases its resistance by about 10%.

The attached images shows the relative size of cross-sections for silver, copper, gold and aluminium of equal mass


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Advantage of use of EHT in transmission of electrical energy.

http://www.sei.ie/Schools/Secondary_Schools/Subjects/Physics/Unit_4_-_Electric_Effects/Advantages_of_EHT/

7% of power generated at large central stations is lost during transmission to the user over high-voltage lines!

A decent sim in VPL of electricity transmission

Use of the chemical effect.

Everyday examples.