How is electricity delivered through the national grid, and how do energy resources compare?
The national grid and the role of step-up and step-down transformers, electrical power and energy calculations, the comparison of renewable and non-renewable energy resources, and the environmental and practical trade-offs involved.
A focused answer to the OCR Gateway GCSE Combined Science A topics P5 and P6 on the national grid and energy resources, covering the grid and step-up and step-down transformers, electrical power and energy, and the comparison of renewable and non-renewable resources.
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What this topic is asking
OCR wants you to describe the national grid and the role of step-up and step-down transformers, carry out electrical power and energy calculations, and compare renewable and non-renewable energy resources with their trade-offs.
The national grid and transformers
Electricity is transmitted across the grid at very high voltage (and therefore low current). The reason is efficiency: for a given power, raising the voltage lowers the current, and the energy wasted as heat in the transmission cables depends on the current (specifically on the current squared), so a lower current wastes far less energy over long distances. A step-up transformer raises the voltage as electricity leaves the power station, and a step-down transformer lowers it again to a safe, usable level (around V) before it reaches homes and businesses. This is why the grid uses transformers at both ends.
Electrical power and energy
These equations let you work out how much energy an appliance uses (from its power and how long it runs) and the power loss in a cable (from the current and resistance). Many Paper 6 questions combine them, for example finding the current from the power and voltage, then the energy from the power and time.
Energy resources
Energy resources are grouped into renewable and non-renewable, and OCR expects you to weigh their advantages and disadvantages.
- Non-renewable resources are fossil fuels (coal, oil and gas) and nuclear fuel. Fossil fuels are reliable and well established but are finite and release carbon dioxide (contributing to climate change) and other pollutants. Nuclear power produces no carbon dioxide when generating but creates radioactive waste and carries a risk of accidents.
- Renewable resources include wind, solar, hydroelectric, tidal, wave and geothermal. They will not run out and generally produce little or no carbon dioxide, but many are unreliable (wind and solar depend on the weather and time of day), have high initial costs, or affect the landscape and habitats.
The best choice depends on reliability, cost, location and environmental impact, and most countries use a mixture of resources.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20194 marksExplain why step-up transformers are used to transmit electricity at high voltage across the national grid, and what step-down transformers do.Show worked answer →
A Physics Paper 6 structured question on the national grid. Reward: a step-up transformer increases the voltage (potential difference) for transmission, which means the current is lower for the same power transmitted. A lower current means less energy is wasted as heat in the transmission cables (because the heating loss depends on the current squared), so transmitting at high voltage and low current makes the grid much more efficient over long distances. Step-down transformers then reduce the voltage again to a safer, usable level before the electricity reaches homes and businesses. Markers credit high voltage giving low current, the reduced energy loss as heat in the cables, and step-down transformers lowering the voltage for safe use.
OCR 20216 marksCompare the advantages and disadvantages of using wind power and using fossil fuels (such as coal) to generate electricity.Show worked answer →
A P6 six-mark extended response, marked on levels. Reward a balanced comparison. Wind power: it is renewable (will not run out), produces no carbon dioxide or other pollutants when generating, and has low running costs; but it is unreliable (only works when the wind blows), the turbines have a high initial cost, and some people object to their appearance or noise. Fossil fuels (coal): they are reliable and can meet demand on demand, and the power stations are well established; but they are non-renewable (finite), release carbon dioxide (contributing to climate change) and other pollutants such as sulfur dioxide (causing acid rain). Top answers give advantages and disadvantages of both, and refer to reliability, cost, and environmental impact (especially carbon dioxide).
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