At what sort of potential difference is power carried away from a power station across the country?

At a very high potential difference, typically hundreds of thousands of volts.

What happens to the potential difference before electricity reaches houses?

It is reduced in stages at substations until it is at the much lower value used in homes.

Why is a much lower potential difference used for the local supply to homes?

A very high potential difference would be far too dangerous in houses, so it is lowered to a value that appliances can use safely.

Where in the grid is the potential difference highest?

In the long transmission cables between the power station and the local substations.

What is a substation used for?

It houses transformers that lower the potential difference so the electricity can be distributed locally.

OCR GCSE Combined Science Physics J250

Electricity

Topic overview Charge, and producing static electricity Transfer of electrons in charging and discharging Current as a rate of flow of charge Charge, current and time Series and parallel circuits, and circuit symbols Current, potential difference and resistance Resistors whose resistance changes, and investigating them Linear and non-linear circuit elements from graphs Net resistance in series and parallel Circuits for measurement, and electrical power

Energy

Topic overview Conservation of energy, and energy stores Energy changes on heating, and calculating them Energy of a moving body, a spring and a raised object Dissipation, and energy transfer in domestic devices Power ratings, and calculating efficiency Reducing unwanted energy transfer, and the rate of cooling

Forces

Topic overview Measuring distance and time, and calculating speed Converting units, and rates Vectors and scalars in motion Distance-time and velocity-time graphs Average speed, and the equations of uniform motion How objects interact, and forces as vectors Newton's first law Newton's second law Work done, and stored energy Power, and Newton's third law Stretching, bending and compressing; elastic and plastic Force and extension, linear and non-linear The spring constant, and work done in stretching Gravitational fields, weight and free fall Calculations with weight and gravitational field strength

Global Challenges

Topic overview Typical speeds and everyday accelerations Reaction time, stopping distance and the dangers of large decelerations Stopping distance, acceleration and collision force calculations Energy resources, and trends in their use The national grid, and step-up and step-down transformers Why the national grid is efficient, and power in a transformer Mains electricity: a.c., d.c. and the domestic supply Live, neutral and earth wires, and electrical danger

Magnetism and Magnetic Fields

Topic overview Permanent and induced magnets, and magnetic poles Magnetic fields, and the dipping compass The magnetic effect of a current, and solenoids

Matter

Topic overview How the atomic model changed, and the structure of the atom The size of atoms, and defining density Density of the states of matter, and density calculations Conservation of mass in changes of state Heating a system, and specific heat capacity Calculations with specific heat capacity and latent heat Gas molecules, temperature and pressure

Radioactivity

Topic overview Protons, neutrons and isotopes Unstable nuclei and the emissions they give out Balancing nuclear equations Electron energy levels, and radiation from atoms Half-life and the randomness of decay Penetration of alpha, beta and gamma Contamination and irradiation, and reducing the hazard

Waves in Matter

Topic overview Amplitude, wavelength, frequency and period The wave equation Transverse and longitudinal waves Modelling waves with ripples and sound Electromagnetic waves as transverse, and energy transfer Frequency and wavelength across the spectrum What our eyes detect, and light as an electromagnetic wave Uses of electromagnetic waves Hazards of ultraviolet, X-rays and gamma rays Investigating reflection and refraction of light

Global Challenges

The national grid, and step-up and step-down transformers

3 things to know
Paper 6 (Physics)

Overview

What the national grid is, the potential differences used for transmission and for homes, what substations do, and where step-up and step-down transformers sit and which coil has more turns.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is the national grid?

Key term

Why are many power stations connected to one network rather than each supplying its own area?

Key term

In the national grid, which type of transformer is used at the power station and which is used near homes?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the national grid?
Model answer
The network of cables, pylons and transformers that carries electrical power from power stations to homes, schools and businesses across the country.
2
At what sort of potential difference is power carried away from a power station across the country?
Model answer
At a very high potential difference, typically hundreds of thousands of volts.
3
What happens to the potential difference before electricity reaches houses?
Model answer
It is reduced in stages at substations until it is at the much lower value used in homes.
4
Why is a much lower potential difference used for the local supply to homes?
Model answer
A very high potential difference would be far too dangerous in houses, so it is lowered to a value that appliances can use safely.
5
Where in the grid is the potential difference highest?
Model answer
In the long transmission cables between the power station and the local substations.
6
What is a substation used for?
Model answer
It houses transformers that lower the potential difference so the electricity can be distributed locally.

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