ELECTRIC CURRENT AND
DIRECT CURRENT CIRCUIT
ELECTRICAL CONDUCTION
Electric Current,I
I=Q/t
Consider a simple closed circuit consists of wires, a battery and a light bulb
Current Density,J
J=I/A
Current flowing through a conductor per unit cross-sectional area
Electrical Conductor in Metal
Charge carrier is free electrons and a lot of free electrons are available in it
move freely & randomly
Q-Ne
Drift Velocity of Charge,Vd
Consider a metal rod of length and cross sectional area,A which is applied to the electric field
n=N/V
RESISTIVITY AND OHM’S LAW
Resistance,R
R=V/I
property which oppose or limits current in an electric circuit
Resistance of a conductor
Length ( l increase,R increase)
Cross Sectional Area (A increase,R decrease)
Type of Material
Temperature (T increase, E increase)
Resistivity
Resistance of a unit area per unit length of the material
p=RA/l
Conductivity
the reciprocal of the resistivity of a material
O=l/p
OHM LAW
V is proportional to the I through it
V=IR
ELECTROMOTIVE FORCE (emf), INTERNAL RESISTANCE AND POTENTIAL
DIFFERENCE
emf
Potential Difference
potential that supplies to a circuit that flows through the extrenal & internal resistance
energy use by a circuit (work done) in bringing a unit
Internal Resistance of Battery
V=IR
E-Ir=IR
E=IR+Ir
is define as the resistance of the chemicals inside a battery
ELECTRICAL ENERGY AND POWER
Energy is liberated per unit time in an electrical device
E=W=QV
W=VIt
P=E/t
P=VI
COMBINATION OF RESISTORS
Parallel
Series
V =V1+V2 +V3
RE = R1+ R2 + R3
I1=I2=I3
I=I1+I2+I3
V1=V2=V3
1/R=1/R1+1/R2+1/R3
KIRCHHOFF’S LAWS
I in =I out
States the algebraic sum of the currents entering any junctions in a circuit must equal the
algebraic sum of the currents leaving that junction.
Kirchhoff's First Law
Kirchhoff's Second Law
States in any closed loop, the algebraic sum of emfs is equal to the algebraic sum of the
products of current and resistance.
E=IR