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Physics Unit 2:
ELECTRICITY
Current: rate of flow of charged particles
I = ∆Q/∆t
Potential difference (voltage): the energy transfer between two points
V = W/Q
(overleaf: IV graphs)
Resistance: a measure of the opposition a material offers the flow of current.
The unit is Ohms (Ω)
R = V/I
Resistance increases with temperature.
Most metals are conductors - there are free electrons to carry a charge.
Power: the rate of work done
P = ∆W/∆t
P = VQ/t
P = VI
Work done
W = VIt
Kirchhoff's First Law
The total current into any point in a circuit is equal to the total current out of that point
Number density of conduction electrons
n = I / qvA
n is large - good conductor
n is small - bad conductor
The Potential Divider
Two resistors connected in series (so current same, p.d. divided between the two) with a supply.
V(1) = R(!)
___ ___
V(2) R(2)
