Current electricity notes

Current Electricity - Study Notes



1. Fundamental Concepts
Electric Current
Electric current is the rate of flow of electric charge through a conductor.
dq
I=
dt
Where:
• I = Current (Ampere)

• q = Charge (Coulomb)

• t = Time
1 Ampere means 1 Coulomb of charge passes a point in 1 second.

Charge Carriers
Charge carriers are particles responsible for the flow of electric current.

• Metals: electrons

• Electrolytes: positive and negative ions

• Semiconductors: electrons and holes


Drift Velocity
Drift velocity is the average velocity with which charge carriers move through a conductor
when an electric field is applied.
I
vd =
nqA
Where:
• n = number density of charge carriers

• q = charge of carrier

• A = cross-sectional area

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, Relation with electric field:

vd = µE
where µ is mobility.
—


2. Key Formulas & Laws
Ohm’s Law
Ohm’s Law states that the current through a conductor is directly proportional to the
potential difference across it (at constant temperature).

V ∝I

V = IR
Where

• V = potential difference

• I = current

• R = resistance

—
Microscopic Derivation
Force on an electron:

F = qE
Acceleration:
qE
a=
m
Drift velocity:
qEτ
vd =
m
Current:

I = nqAvd
Substitute vd :
 
qEτ
I = nqA
m


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