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The National Grid is supplied mainly from power stations which have overall efficiencies of up to about 40% Table 1 shows the average power requirements of a large paper-manufacturing business (a paper mill) - AQA - A-Level Physics - Question 4 - 2018 - Paper 6
Question 4
The National Grid is supplied mainly from power stations which have overall efficiencies of up to about 40% Table 1 shows the average power requirements of a large ... show full transcript
Worked Solution & Example Answer:The National Grid is supplied mainly from power stations which have overall efficiencies of up to about 40% Table 1 shows the average power requirements of a large paper-manufacturing business (a paper mill) - AQA - A-Level Physics - Question 4 - 2018 - Paper 6
Step 1
explain why the maximum theoretical efficiency of a heat engine is much less than 100%
Answer
The maximum theoretical efficiency of a heat engine is defined by the second law of thermodynamics. It can be derived from the Carnot efficiency formula, which is expressed as:
ext{Efficiency} = 1 - rac{T_C}{T_H}Here, is the absolute temperature of the cold reservoir, and is the absolute temperature of the hot reservoir. Since no engine can operate between two temperature reservoirs without having some thermal losses, the efficiency will always be less than 100%. Additionally, real heat engines experience various inefficiencies due to friction, heat losses, and incomplete combustion.
Step 2
use the information above, including the numerical data, to come up with a conclusion
Answer
Given the power requirements from Table 1, the total power needed for the paper mill is:
- Driving electric motors: 49 MW
- Heating: 141 MW
- Electrical equipment: 8 MW
Total Power Requirement = 49 + 141 + 8 = 198 MW
For the CHP system, the generator has an output of 60 MW with an efficiency of 36%. Therefore, the actual power output can be calculated as:
Since this output does not meet the total power requirement of 198 MW, it will not be sufficient to cover the energy demand alone. Additionally, using only the National Grid may subject the factory to power cuts and higher costs. The most reliable advice would be to investigate additional energy sources or combination systems that ensure a robust and efficient energy supply.