Contains the full lesson along with a supporting toolkit, including teachers’ notes.
Today we are becoming increasing aware of the need to make more efficient use of non-renewable energy resources. Traditional fossil fuel power stations are less than 40% effi cient. In other words, more than 60% of the energy in the fuel is lost as heat to the environment. By combining district heating with power generation efficiencies of 60% to 80% can be achieved.
Before we can use it electricity must get to the end users. This is done through the transmission and distribution systems. Metallic conductors, such as copper and aluminium, carry the electric current to our homes and places of work. However, some energy is lost along the way as heat because even the best conductors have some electrical resistance.
These losses have been reduced from about 13% in 1960 to about 7.5% in 2016. Can we reduce these losses even further?
In a letter dated 20th March 1800 Alessandro Volta (1745–1827) described the construction of a battery. He demonstrated his invention in Paris and news of the device spread quickly. For the first time a continuous electric current could be generated and scientists in Europe and America began experimenting with their own versions of the battery.
Before long they had discovered two effects of electric current:
• a heating effect and
• a chemical effect.
That year (1800) Nicholson and Carlisle decomposed water into hydrogen and oxygen ― a process known as electrolysis. Around 1808 Humphry Davy discovered several new elements using electrolysis: potassium, sodium, barium, calcium and magnesium. It is somewhat surprising that the magnetic effect of electric current was not discovered until 1820.
Although the heating effect of electric current is more obvious it was not studied in detail until the 1840s. Part of the reason for this was the rather poor understanding at that time of the concepts of heat and energy — concepts that we take for granted today.
James Joule (1818–1889) spent much of his life studying these two concepts. In 1840 he replaced steam engines in his brewery with recently developed electric motors. He began to study the heat loss from conductors. Even the best conductors (silver and copper) show some resistance to electric current and may become quite hot if they carry a large electric current.
In 1841 Joule discovered that the rate of heat loss from a conductor was proportional to its resistance multiplied by the square of the electric current. Today we express this relationship mathematically as follows: P = R x I2 where P is the power (that is the energy produced per unit time), R is the resistance and I is the electric current. This was an important discovery.