Physics Chapter 8 Flashcards
Define the energy density and specific energy of a fuel. [2]
Energy density is the energy released by the fuel per unit volume. [1]
Specific energy is the energy released by the fuel per unit mass. [1]
State three differences between renewable and non-renewable energy sources. [3]
Renewable energy will not be depleted but non-renewable energy will. [1]
Renewable energy can be re-generated but non-renewable energy cannot. [1]
Rate of consumption of renewable energy is smaller than that of production but the rate of consumption is greater in non-renewable energy. [1]
Energy degradation takes place in the energy transformations which occur in the generation of electrical power. Explain what is meant in this context by energy degradation. [2]
Some energy is converted to thermal energy during energy transformations. [1]
The thermal energy is lost to the surroundings which cannot produce useful energy. [1]
Describe the difference between photovoltaic cells and solar heating panels on producing energy. [1]
Photovoltaic cells convert solar energy into electrical energy but solar heating panels convert solar energy into thermal energy.
State two reasons why the albedo of Earth must be given as an average value. [2]
The weather conditions are different at different places. The places covered by cloud have higher albedo. [1]
The colour of the surfaces of the lands are different at different places. The places covered by snow have higher albedo. [1]
State three reasons why the efficiency of a wind turbine cannot be 100%. [3]
Not all KE of the wind can be converted to KE of the blades. [1]
Energy is lost to thermal energy due to friction in the turbine. [1]
Energy is lost to thermal energy due to resistance in the electrical wires of the system. [1]
Outline, with reference to the energy conversions in the machine, the main features of a conventional horizontal-axis wind generator. [3]
The blades of the turbine are pushed by the wind. [1]
When the wind passes through the blades, its KE changes to the KE of the blades. [1]
Then the KE of the blades changes to electrical energy
produced by the generator. [1]
Outline the purpose of the heat exchanger in a nuclear reactor. [1]
It transfers thermal energy from the nuclear reactor to the steam.
Outline the purpose of the moderator in a nuclear reactor. [2]
It reduces the speed of the neutrons. [1]
It increases the chance of capturing the neutrons by the fuel (U-235) so that nuclear fission can occur. [1]
State two advantages and two disadvantages of using nuclear power compared to using fossil fuels. [4]
Advantages:
1. It does not produce air pollution and greenhouse gases.
2. Its energy density is much higher.
Disadvantages:
1. It produces radioactive wastes.
2. The nuclear and radiation accidents could be catastrophic.
A nuclear power station uses uranium-235 (U-235) as fuel. Outline the processes and energy changes that occur through which thermal energy is produced. [4]
Neutrons are produced during a U-235 nuclear fission. [1]
The fast moving neutrons have high KE. [1]
The KE of the neutrons changes to the thermal energy of the moderator. [1]
The thermal energy of the moderator is transferred to the coolant. [1]
Any nuclear fuel available to the islanders must be enriched before it can be used. Outline why fuel enrichment is needed. [2]
U-235 can capture fast moving neutrons to undergo nuclear fission. U-238 does not. [1]
However, the percentage of U-235 in naturally occurring ores is too low to support fission. [1]
Therefore, the percentage of U-235 has to be increased.
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. [3]
Similarity:
The fast-moving neutrons collide with the nuclei in the control rods and in the moderator. [1]
Difference:
1. Control rods absorb the fast-moving neutrons but the moderator (water) only slow down the neutrons.
2. Control rods reduce the rate of reaction but the moderator maintains the reaction. [1]
Suggest two reasons why pump storage hydroelectric scheme is a renewable energy. [2]
First, the source will not run out. [1]
Second, the water can be pumped back and replaced in a short time. [1]
Describe the main principles of the operation of a pump storage hydroelectric scheme. [3]
At off peak hours, electricity is used to pump the water from the lower reservoir to the higher reservoir. Potential energy is stored in the water. [1]
At peak hours, the water flows from the higher reservoir to the lower reservoir. Potential energy of the water is released. [1]
The water drivers the turbines of the generators to produce electricity. [1]
