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Current vs. Electron flow…read more

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Charge, Current & Potential
Difference
Charge (Q) ­ charge is measured in coulombs (C).
A single electron carries a charge of 1.6 x 10-19 C.
Current (I) - is measured in amperes (A).
Current is the rate of flow of charge. A current of 1 A means that 1 coulomb of charge flows
past a point in a circuit every second. ( 1 A = 1 C s-1 ) Current is measured in a circuit using an
ammeter which is placed in series with the component of interest in the circuit.
I = current in amperes, A
DQ = charge in coulombs, C
Dt = time in seconds, s
Potential difference (V) - is measured in volts (V).
Potential difference is the work done per unit charge. A potential difference of 1 V means that
1 joule of work is done per coulomb of charge. ( 1 V = 1 J C-1) Potential difference in a circuit is
measured using a voltmeter which is placed in parallel with the component of interest in the
circuit.
V = potential difference in volts, V
W = work done or energy transferred in joules, J
Q = charge in coulombs, C…read more

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Current/Voltage
Characteristics
ohmic conductor
Current is directly proportional to potential difference. Doubling the
potential difference doubles the current in the circuit. The
resistance remains the same. Plotting a graph of potential
difference against current gives a straight line passing through the
origin (0,0).
non ohmic conductor
Curret is not directly proportional to p/d. Creates a sigmoid curve
(filament bulb) or a biased curve for a
diode.…read more

Slide 5

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Resistance and Resistivity
The resistance of a piece of wire at a
constant temperature depends on both the
length of the wire and the cross-sectional
area of the wire. Also the temperature and
material type affects resistance of a wire.
Resistivity is measured in Ohm meters (m)…read more

Slide 6

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Kirchoff's first law = the sum of the
Circuits currents flowing into a junction of wires
must equal the sum of the currents
flowing away from the junction of wires
Series:
Current = SAME across components
Voltage = SPLIT across components (but is equal
to terminal p.d)
Resistance = ADDED TOGETHER
Parallel:
Current = SPLIT across branches(each branch
treated as a series circuit)
Voltage = SAME on each branch
Resistance = SPECIAL…read more

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