Fig. 1 shows a hydroelectric station in a valley. Water stored behind a dam flows down a pipe and turns a turbine connected to a generator. The water then l...
Question 1 Report
Fig. 1 shows a hydroelectric station in a valley. Water stored behind a dam flows down a pipe and turns a turbine connected to a generator. The water then leaves at a lower level. A student is asked to consider the energy transfers rather than the electrical circuit inside the station.
(a) State the energy store of the water behind the dam. [1]
(b) Complete this sequence of useful energy transfers: gravitational potential energy of water → kinetic energy of water → __________ energy of turbine → electrical energy. [1]
(c) Describe two ways in which energy is dissipated in the station. [3]
Answer Details
(a) Water stored high behind the dam has a gravitational potential energy store. [1]
(b) The missing store is the kinetic energy of the turbine. The moving water makes the turbine rotate. [1]
(c) Energy is dissipated in several unwanted transfers. Any three valid points gain credit:
- Friction in the turbine transfers energy to thermal energy stores.
- Water resistance or air resistance transfers energy by heating.
- Some energy is transferred by sound.
- Electrical resistance in cables transfers energy to thermal energy stores.
These transfers mean not all the water’s original gravitational potential energy becomes useful electrical energy. [3]
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