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G482 Physics
Figure when I'm revising…read more

Slide 2

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Module 1 - Electric Current
Learning objectives:
· Charge and current
-what is meant by conventional current and electron
flow…read more

Slide 3

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Charge and Current
· Current is the rate of flow of charged particles
· Electric current in a metal is due to the movement of
electrons, whereas in an electrolyte the current is due to the
movement of ions
· A wire is made of metal with many negatively charged
electrons. These are conduction or free electrons. The atoms
of a metal bind tightly together forming a regular array. In a
metal such as copper, one electron from each atom breaks
free to become a conduction electron, the atom remains a s
positively charged ion Since there equal numbers of negative
free electrons and positive ions. The metal has no overall
charge.…read more

Slide 4

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Sometimes a current is a flow of positive charges, e.g.
a beam of protons produced in a particle accelerator.
The current is in the same direction as the particles.
· Sometime a current is due to both positive and
negative charges, e.g. when charged particles flow
through a solution. A solution which conducts is called
electrolyte and contains positive and negative ions.
· These +ve and ­ve ions move in opposite directions
when the solution is connected to a cell.…read more

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Note: there is a current at all points in the circuit as soon as the
circuit is completed. We do not have to wait for the charge to
travel around the cell because there are charged electrons
already present throughout the metal
· The direction of conventional current is from the positive
terminal, around the cell to the negative terminal.
· When the cell is connected to the wire, it exerts an electrical
force on the conduction electrons that makes them travel along
the length of the wire. Electrons are negatively charged, so they
flow away from the negative terminal of the cell to positive.
· The direction of electron flow is in the opposite direction to
conventional current.…read more

Slide 6

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Q = I t
· Coulomb ­ 1C is the amount of charge which flows past a point
in a time of 1s when the current is 1A
· Kirchhoff's first law: The SUM of current entering any point in
a circuit is equal the SUM of current leaving that same pint. (
This is a consequence of conservation of charge)
· It's impossible to have charge on its own; charge is always
associated with particles having mass
· Mean drift velocity: When connected to a battery or an
external supply, each electron within the metal experiences an
electrical force that causes it to move towards the positive
end of the battery. The electrons randomly collide with the
fixed but vibrating metal ions. Their journey along the metal is
very haphazard. The actual velocity of an electron between
collisions is around 106ms-1…read more

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