Chapter 12
Electric Circuits
Abstract Chapter 12 is mainly concerned with the analysis of electric network
employing Kirchhoff’s laws. Problems are solved under resistivity, Joule heating,
emf, internal resistance, arrangement of cells, electric instruments such as ammeter,
voltmeter, potentiometer and Wheatstone bridge.
12.1 Basic Concepts and Formulae
Electric current (i) is defined as the rate at which the net charge q passes through a
cross-section of a conductor
i = q/t
(12.1)
The instantaneous current is defined by
i = dq/dt
The current density ( j) is given by
j = i/A
(12.2)
where A is the cross-sectional area.
The Drift Velocity
v d = i/nAe = j/ne
(12.3)
where n is the number of electrons per unit volume
Resistance (R) and Resistivity (ρ)
R = ρ L/A
(12.4)
535
Electric Circuits
Abstract Chapter 12 is mainly concerned with the analysis of electric network
employing Kirchhoff’s laws. Problems are solved under resistivity, Joule heating,
emf, internal resistance, arrangement of cells, electric instruments such as ammeter,
voltmeter, potentiometer and Wheatstone bridge.
12.1 Basic Concepts and Formulae
Electric current (i) is defined as the rate at which the net charge q passes through a
cross-section of a conductor
i = q/t
(12.1)
The instantaneous current is defined by
i = dq/dt
The current density ( j) is given by
j = i/A
(12.2)
where A is the cross-sectional area.
The Drift Velocity
v d = i/nAe = j/ne
(12.3)
where n is the number of electrons per unit volume
Resistance (R) and Resistivity (ρ)
R = ρ L/A
(12.4)
535