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Slide 1

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Physics topic 19- current of
By Olivia Blanchet…read more

Slide 2

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Electic current
· Electric current is a flow of electric charges. A lamp
lights because charged particles are moving through
· Ions can only vibrate about their fixed point, but
electrons are free to move randomly from one ion to
another through the lattice.
· When a battery is attached to a wire. The free
electrons are repelled by the negative terminal but
are attracted to the positive one.
· They still have random movement but now move in
the same direction. This is a flow of charge- an
electric current!…read more

Slide 3

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Charge and coulomb
Charge coulomb
· Electric charge flows along · The unit of electric charge is
wires. the coulomb.
· It flows along the complete · 1 coulomb is the amount of
conducting path. charge that passes a point
· Charge is the source of electric when a current of 1 ampere
force. flows for 1 second.
· Electric charges can be either · The charge on 1 electron is 1.6
positive or negative. x 10 ^-19 Coulombs.…read more

Slide 4

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Potential difference and the Volt
Potential difference The Volt
· The coulombs entering a lamp · P.d is measured in Volts and is
have electrical potential often called Voltage.
energy; those leaving have very · If the p.d is one volt, then 1
little potential energy. joule of electrical energy is
· The p.d between two points is transferred for each coulomb
the electrical potential energy of charge.
transferred to other forms, per
coulomb of charge that passes
between two points.…read more

Slide 5

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Resistance and the ohm
Resistance The Ohm
· The greater the resistance of a · Resistance is measured in
component the more difficult it Ohms.
is for charge to flow through it. · The current through a metal
· The electrons make many wire is directly proportional to
collisions with a tungsten the p.d across it ( providing
fillament which gives it high that temperature remains
resistance. constant)- this is Ohm's law.
· The resistance of a conductor
is the ratio of the p.d applied
across it, to the current passing
through it.…read more

Slide 6

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· The resistance of a wire at a constant
temperature depends on it's dimensions and the
material from which it's made.
· Every material has a property called it's
resistivity `rho' it is measured in ohm metres.
· If we know the resistivity, the cross-sectional
area and the length of a sample of material we
can calculate it's resistance.…read more

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