(a)(i)
For the correct answer:
gravitational OR potential
Water stored behind a dam is at a height, so it possesses gravitational potential energy due to its position in the Earth’s gravitational field.
(a)(ii)
For the correct answer:
generator AND turbine
A hydroelectric station uses falling water to spin a turbine, which is connected to a generator that converts the mechanical energy into electrical energy. Boilers, cooling towers, and solar cells are not used in this process.
(b)(i)
For the correct answer:
step-down
The transformer shown is near the homes and factories, reducing the high transmission voltage to a lower, safer voltage for domestic and industrial use.
(b)(ii)
For the correct answer (any two):
lower current (in cables)
reduced power / energy loss / increased efficiency OR reduced heating losses
thinner / cheaper / lighter cables
pylons can be further apart / not so strong
Transmitting at high voltage allows a lower current for the same power $(P = IV)$. A lower current reduces thermal energy lost as heat in the cables $(P = I^2R)$, improving efficiency and allowing thinner cables.
(c)
For the correct answer (any two advantages from):
no fuel costs
renewable
no air pollution / no $\mathrm{SO}_2$ / no acid rain
no greenhouse gases / $\mathrm{CO}_2$ emissions
no fuel to transport
creates lakes for recreation / tourism
quick start-up time owtte
For the correct answer (any two disadvantages from):
large area of land flooded
damage to wildlife habitats
population displacement
limited number steep sided valleys owtte
changes to water provision (downstream)
(output) can be affected by lack of rain / drought
Hydroelectric power uses a renewable source (water) and produces no direct air pollutants, unlike burning coal. However, building dams floods large areas, displacing communities and damaging ecosystems, and power output depends on seasonal rainfall.
