| Date | May 2015 | Marks available | 3 | Reference code | 15M.2.SL.TZ1.4 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Deduce, Explain, and Suggest | Question number | 4 | Adapted from | N/A |
Question
This question is about energy sources.
A small island is situated in the Arctic. The islanders require an electricity supply but have no fossil fuels on the island. It is suggested that wind generators should be used in combination with power stations using either oil or nuclear fuel.
Suggest the conditions that would make use of wind generators in combination with either oil or nuclear fuel suitable for the islanders.
Conventional horizontal-axis wind generators have blades of length 4.7m. The average wind speed on the island is 7.0ms−1 and the average air density is 1.29kgm−3.
(i) Deduce the total energy, in GJ, generated by the wind generators in one year.
(ii) Explain why less energy can actually be generated by the wind generators than the value you deduced in (b)(i).
The energy flow diagram (Sankey diagram) below is for an oil-fired power station that the islanders might use.
(i) Determine the efficiency of the power station.
(ii) Explain why energy is wasted in the power station.
(iii) The Sankey diagram in (c) indicates that some energy is lost in transmission. Explain how this loss occurs.
The emissions from the oil-fired power station in (c) are likely to increase global warming by the enhanced greenhouse effect.
Outline the mechanism by which greenhouse gases contribute to global warming.
Nuclear fuel must be enriched before it can be used. Outline why fuel enrichment is needed.
The nuclear equation below shows one of the possible fission reactions in a nuclear reactor.
\[\left( {{}_{\rm{0}}^{\rm{1}}{\rm{n + }}{}_{92}^ \cdots {\rm{U}} \to {}_ \ldots ^{92}{\rm{Kr + }}{}_{56}^{141}{\rm{Ba + }} \ldots {}_0^1{\rm{n}}} \right)\]
Identify the missing numbers in the equation.
A nuclear reactor requires both control rods and a moderator to operate. Outline, with reference to neutrons, one similarity and two differences in the function of each of these components.
Markscheme
needs to be windy/high average wind speeds; space/land/room for wind turbines;
ability to import oil/nuclear fuel;
ability to dispose of nuclear waste;
comment relating to need for geological stability;
(i) π4.72 or 69.4 m2;
power = 15300 to 15400 W;
470 to 490 GJ;
(ii) wind must retain kinetic energy to escape or not all KE of wind can be converted to KE of blades;
energy lost to thermal energy (due to friction) in generator/turbine/dynamo;
turbine will suffer downtime when no wind/too much wind;
Allow any two relevant factors.
(i) indication that energy supplied to islanders is output and chemical energy
input / \(\frac{8}{{25}}\) used;
32% / 0.32;
(ii) energy/it is wasted due to inefficient burning of oil / thermal/heat energy loss to surroundings/environment / electrical energy is used to run the power station’s systems / energy/it is wasted due to frictional losses in the turbine/generator;
(iii) heating of wires by electric current / inefficient transformers;
radiation emitted by Earth in (long wavelength) infrared region;
frequency corresponds to resonant frequency of greenhouse gases (either vibration or difference in energy levels);
radiation absorbed by greenhouse gases is (partly) re-radiated back to Earth;
percentage of U-235 in naturally occurring ores is too low to support fission or naturally occurring U-238 does not undergo fission;
percentage of U-235 (which can usefully capture thermal neutrons) is increased;
