Ex.7. Complete the article about electric and diesel-electric locomotives using the words in the box.

An electric locomotive is one that is (1)... by an external energy (2)…, most often via overhead electric lines. This differs from a diesel-electric locomotive, which has an onboard fuel tank and a diesel-powered generator to provide electricity for its motors. Purely electric power has numerous advantages over diesel-electric power, explaining the choice of electric locomotives for use in high-speed trains.

Firstly, an electric locomotive needs to carry neither a generator nor fuel. Its mass is, therefore, lower than a diesel-electric equivalent. This results in a significant efficiency (3)…, as the electric locomotive’s smaller mass means less (4)… is done – measured as a total number of (5)… - on a given journey. For a comparable rate of acceleration, its motors are also required to provide less (6) ….

As they use a lower (7)…., this means less (8)… motors can be used, making them smaller, thus further reducing weight and improving (9)… In addition, electric locomotives use only (10)… energy. This means there is no need to (11)… energy from one (12)… to another on board the train (electricity can be generated more efficiently in power stations).

In a diesel-electric unit, the energy conversion process starts with (13)… energy, which is (14)… within the hydro-carbon compounds of diesel. This fuel is burned to produce (15)… energy, and the heat is then converted by the engine into (16)… energy, which provides the movement to drive the train. This process is a very long way from being 100% (17)… - only a small percentage of the initial chemical energy is converted to the (18)… energy that is actually used to drive the train, with a significant percentage being (19)… into the air in the form of heat, constituting (20)… energy.