# Current and Charge

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- Created by: ColourPages
- Created on: 05-04-17 18:27

## Electric Current

- The rate of flow of charge
- Symbol I
- Measured in amperes ( A )
- Normally a flow of electrons in metals
- Or flow of ions in electrolytes

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## Amperes

- Base SI unit of electric current
- Symbol (A)
- Defined as the current flowing in two parallel wires in a vacuum 1m apart such that there is an attractive force of 2 x 10 -7 N per metre length of wire between them

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## Positive

One type of electric charge, attract negative repel other positives

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## Negative

A type of electric charge such that it repels other negative charge and attracts positive charge.

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## Coulomb (C)

- The derived SI unit of electric charge.
- 1 coulomb of electric charge passes a point each second when there is a current of one amp
- 1 coulomb = 1 amp x second

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## Electric Charge

- Physical property (symbol of q or Q)
- Positive or negative
- Measured in coulombs or as a relative charge

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## Ion

- An atom that has either lost or gained electrons
- Has a net charge

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## Relative Charge

- A simplified measurement of the electric charge of a particle or object
- Measured in multiples of the elementary charge (q or e)

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## Quantise

- The availabilty of some quantities only in certain discrete values
- Examples are elementary charge

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## Conventional Current

- A model used to describe electric current in a circuit
- Travels from positive to negative

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## Free Electrons

- An electron in a metal that is not bound by an atom and is free to move.
- AKA a delocalised electron

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## Electrolytes

- A liquid containing ions that are free to move and so conduct electricity

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## Ionic Solutions

- An ionic compound dissolved in a liquid
- This forms an electrolyte

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## Cations

A positively charged ion attracted to a cathode. (Which are negatively charged)

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## Anion

A negatively charged ion attracted to an anode.

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## Cathode and Anode

Cathode - a negatively charged electrode

Anode - a positively charged electrode

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## Ammeter

- A device used to measure electric current
- Placed in series in a circuit and ideally has zero resistance

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## Resistance

- Property of a component calculated by divided the potential difference across it by the current in it.
- Symbol R, unit ohm

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## Potential Difference

- Defined as the energy transferred from electrical to other forms per unit charge

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## Conservation of charge

- States electric charge cannot be created or destroyed
- Total charge in any interaction is the same before and after said interaction

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## Kirchhoff's First Law

- At any point at a circuit the current entering is the same as the current leaving
- Electrical charge is conserved

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## Number Density

- The number of free electrons per cubic metre of material.
- Symbol n, unit 1/m-3

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## Semi-conductors

- A material with a lower number density than a typical conductor.
- Number density typically of order 10 to the 17 1/m3

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## Mean Drift Velocity

- The average velocity of electrons as they move through a wire
- Symbol v, units metres per second

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