Describe how static electricity and sparking are produced, explain attraction and repulsion between charged objects, and relate these effects to electron transfer.
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GCSE Physics Revision
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GCSE Physics revision
Static charge
Static electricity (physics only)
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AQA student objectives
Learning pathway
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Apply the scientific explanation of static charge to a relevant example.
Analyse a new situation involving static charge and explain the scientific reasoning.
Revision summary
Key knowledge
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What is Static Electricity?
- Static electricity is the buildup of electric charge on the surface of insulating materials, which can cause sparks when discharged.
- All materials contain positive protons and negative electrons, but normally these cancel out, making most materials electrically neutral.
- When two insulating materials are rubbed together, friction causes electrons to transfer from one material to the other.
Conductors vs Insulators
- In conducting materials such as metals, electrons can move freely, so any transferred electrons flow straight back and no static charge builds up.
- In insulating materials such as a polythene rod or cloth, electrons cannot flow back after being transferred, so a static charge remains.
- The material that loses electrons gains a positive static charge, whilst the material that gains electrons gains a negative static charge.
Direction of Electron Transfer
- The direction of electron transfer depends on the specific materials being rubbed together.
- For example, rubbing a polythene rod with a cloth causes electrons to transfer onto the polythene rod, making it negatively charged and the cloth positively charged.
- Rubbing an acetate rod with a cloth causes electrons to transfer onto the cloth instead, making the acetate rod positively charged and the cloth negatively charged.
- It is only the negative electrons that are ever transferred — a positive charge arises from losing electrons, not from gaining protons.
Sparks and Potential Difference
- As more electrons are transferred, the size of the charge increases and a potential difference develops between the charged material and the Earth.
- Earth and earthed objects are always at zero volts, so a large enough potential difference can cause electrons to jump across the gap between the charged object and an earthed object.
- The jumping of electrons across a gap is what produces a spark.
Static Charge on Conductors
- Although less common, static charge can also build up on conductors under certain conditions.
- For example, a car's metal frame can build up charge through contact with the wind, which transfers electrons onto the car.
- Touching a charged car can result in a small electric shock, as the car discharges to Earth through your body via a small spark.