Question 19M.3.hl.TZ1.15b(ii)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.hl.TZ1.15b(ii) |
| Level | hl | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | b(ii) | Adapted from | N/A |
Natural gas is an energy source composed mainly of methane.
Natural gas is burned to produce steam which turns turbines in an electricity generating power plant.
The efficiency of several sources for power plants is given below.
Hydroelectric power plants produced 16% of the world’s energy in 2015, down from 21% in 1971.
Suggest why hydroelectric power production has a higher efficiency than the other sources given in (b) and why its relative use has decreased despite the high efficiency.
Reason for higher efficiency:
Reason for decreased use:
[2]
Reason for higher efficiency:
no heat/energy loss in producing steam
OR
no need to convert chemical energy of the fuel into heat and then heat into mechanical energy
OR
direct conversion of «gravitational» potential energy to mechanical energy [✔]
Note: Accept “less energy lost as heat” but do not accept “no energy lost”.
Reason for decreased use:
limited supply of available hydroelectric sites
OR
rapid growth of electrical supply in countries with little hydroelectric potential
OR
not building «new hydroelectric» dams because of environmental concerns [✔]
Note: Accept “new/alternative/solar/wind power sources «have taken over some of the demand»”.
Accept “lower output from existing stations due to limited water supplies”.
Suggesting reasons for hydroelectric power having higher efficiency but lower relative use than other energy sources in was not answered well by most candidates. Often the reasons for higher efficiency were given in vague terms that did not meet the detail required.
