Page 82 - Physics Coursebook 2015 (A level)

Cambridge International AS Level Physics
70
The idea of energy
The Industrial Revolution started in the late
18th century in the British Isles. Today, many
other countries are undergoing the process of industrialisation (Figure 5.1). Industrialisation began as engineers developed new machines which were capable of doing the work of hundreds of craftsmen and labourers. At first, they made use of the traditional techniques of water power and wind power. Water stored behind a dam was used to turn a wheel,
which turned many machines. By developing new mechanisms, the designers tried to extract as much
as possible of the energy stored in the water. Steam engines were developed, initially for pumping water out of mines. Steam engines use a fuel such as coal; there is much more energy stored in 1 kg of coal than in 1 kg of water held behind a dam. Steam engines soon powered the looms of the textile mills, and the British industry came to dominate world trade in textiles.
Nowadays, most factories and mills rely on electrical power, generated by burning coal or gas at a power station. The fuel is burnt to release its store of energy. High-pressure steam is generated, and this turns a turbine which turns a generator. Even in the most efficient coal-fired power station, only about 40% of the energy from the fuel is transferred to the electrical energy that the station supplies to the grid.
Engineers strove to develop machines which made the most efficient use of the energy supplied to them. At the same time, scientists were working out the basic ideas of energy transfer and energy transformations. The idea of energy itself had to be developed; it was
Figure 5.2 The jet engines of this aircraft are designed to make efficient use of their fuel. If they were less efficient, their thrust might only be sufficient to lift the empty aircraft, and the passengers would have to be left behind.
not obvious at first that heat, light, electrical energy and so on could all be thought of as being, in some way, forms of the same thing. In fact, steam engines had been in use for 150 years before it was realised that their energy came from the heat supplied to them from their fuel.
The earliest steam engines had very low efficiencies – many converted less than 1% of the energy supplied to them into useful work. The understanding of the relationship between work and energy led to many ingenious ways of making the most of the energy supplied by fuel.
This improvement in energy efficiency has led to the design of modern engines such as the jet engines which have made long-distance air travel a commercial possibility (Figure 5.2).
Figure 5.1 Anshan steel works, China.