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Chapter 3 : Electric current & Direct Current Circuit by Tina :star:…
Chapter 3 : Electric current & Direct Current Circuit by Tina :star:
3.1 Electric Conduction
Electric Current, I
Direction of Electric Current / field : +ve :arrow_forward: -ve
Direction of Electron Flows : -ve :arrow_forward: +ve
Current Density, J
Direction of Current Density :
Same Direction
of I
Drift Velocity of Charges, Vd
3.2 Resistivity & Ohm's Law
Resistance, R
property which opposes / limits current in electrical circuit
Resistivity, p
Resistivity depends on
type of material
&
temperature
A good electric conductor have a very
low resistivity
.
A good insulator have very
high resistivity
Resistance of conductor depends on
length
&
cross-sectional area
units is Ohm meter
Conductivity, σ
Ohm's Law
:
Voltage :zap: drop across a conductor, V is propotional to the current, I
if physical condition & temperature are constant.
or we can write as J = σE
3.3 Electromotive Force, (emf), Internal Resistance & Potential Difference
Emf, Ɛ & Potential Difference, V
: V = Ɛ - Ir (internal resistance)
Internal Resistance of a battery, r
r = Vr / I : Resistance of the chemical inside the battery (cell) between the poles.
3.4 Electrical Energy & Power
Electrical Energy, E
or Q = It , W = E
Power, P
3.5 Combinations of Resistors
3.6 Kirchhoff's Law
First Law
:
ΣIin = ΣIout
Second Law
:
ΣƐ = ΣIR
:arrow_forward:Direction of loop, :arrow_forward: Ɛ = +Ɛ
:arrow_backward: Direction of loop, :arrow_forward: Ɛ = -Ɛ
:arrow_forward:Direction of loop, :arrow_forward: IR = +IR
:arrow_backward: Direction of loop, :arrow_forward: IR = -IR
3.7 Electrical Measurement Devices
Ammeter
measures current :bulb:
Connected in
series
Zero
resistance
Voltmeter
measures voltage :zap:
connected in
parallel
infinite
resistance
Ohmmeter
measure resistance :forbidden:
connected in
series
Galvanometer
Current- sensitive device
:warning:
Apply Magnetic principle
Shunt
: to convert to
Ammeter
, connected in
parallel
with Galvanometer ( Rs << r )
Multiplier
: to convert to
Voltmeter
, connected in
series
with Galvanometer ( Rs >> r )
