# AQA Physics Revision - Electricity

Detailed notes on Electricity from textbook

(well, short but detailed)

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Static electricity
Some insulating materials become electrically charged when rubbed together.
Same Charges Repel
Opposite Charges Attract
Conductors cannot be electrically charged as they lose the charge to Earth
When materials are rubbed against each other:
Negatively charged particles (electrons) move from one material to another.
The material that loses electrons becomes positively charged
The material that gains electrons becomes negatively charged
Equal amount of charge but opposite charges between materials
Charge can be detected when two charged objects of the same type are brought close together
They will repel each other if both are positive or negative
If the charges are opposite OR if one is charged and the other isn't, they will attract together
Charged objects can be discharged by connecting it to Earth with a metal wire or other conductor. If
the potential difference (voltage) is very large, a spark can jump across the gap between the charged
object and the conductor, which can be dangerous.
Static electricity can be useful in different ways:
In electrostatic precipitators, it can help by removing the smoke given off from power stations that
burn fossil fuels, which can damage buildings and cause breathing difficulties. As smoke contains
tiny solid particles, such as unreacted carbon, the machine can use this to help remove them from
the gases. It first passes through a negatively charged metal grid which gives them a negative
charge, which are attracted to the collect plates which are positively charged and collecting plates
beneath them help remove the smoke particles, leaving the waste gases smoke free.
Photocopiers and laser printers also use static electricity. The image of the original document is
projected onto a positively charged copying plate. When light falls onto the plate, the electrical
charges leaks away. Negatively charged black toner particles are attracted to the remaining
positive areas. As paper is placed over the copying plate: toner is transferred to the paper and
heated to make it stick.

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Circuits
Electrical circuits can be represented by circuit diagrams and the different components are shown by
using standard symbols. Components can be connected in series, or in parallel. The characteristics of
the current and potential difference (voltage) are different in series and parallel circuits.
Only complete circuits work and if it is a short circuit, it will not work
In a series circuit:
The current that flows across each component connected in series is the same.…read more

### Page 3

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Resistance and resistors
Resistance is measured in ohms or and can be calculated from the potential difference across a
component and the current flowing through it.
Resistance can be measure with this equation:
Potential Difference (V) = Current (A) x Resistance ()
Current = P.D / Resistance
Resistance = P.D / Current
The more components in a circuit, the higher the total resistance and less current will flow.…read more