Int. to Electrical-Electronics
Engineering
Asst. Prof. Dr. Alper ŞİŞMAN
Ohms Law
• What is potential?
– The potantial of a point is defined : as the
required energy to bring the unity charge from
infinity to that point in an electric field.
– dW=F*dr=> dW = qEdr, Here q is unity! =>
– dW = ((1/4πε)*q/r2)dr=> V=W=∫((1/4πε)*q/r2)dr
and the limits of integration are: r……infinite
Thus the result: V=((1/4πε)*q/r)dr.
– Electric potential is a scalar quantity while electric
field is defined as a vector.
Ohms Law
• Ohm's law states that the current through a
conductor between two points is directly
proportional to the potential difference across
the two points.
• What is voltage difference
• What is current
• Current density J=I/A
• Electric field-current density relation: J=E*sigma,
E=J*rho
• Electric field voltage relation V=E*L
• V=I*(rho* L/A). Here rho L/A is resistance (R) and
V=IR
Faraday's law of induction
• Electromagnetic induction is the production of a
potential difference (voltage) across a conductor
when it is exposed to a varying magnetic field.
• Faraday's law of induction is a basic law of
electromagnetism predicting how a magnetic field
will interact with an electric circuit to produce an
electromotive force (EMF). It is the fundamental
operating principle of transformers, inductors, and
many types of electrical motors, generators and
solenoids.
diagram of Faraday's
iron ring apparatus:
• When the flux changes—because B changes,
or because the wire loop is moved or
deformed, or both—Faraday's law of
induction says that the wire loop acquires an
EMF, defined as the energy available from a
unit charge that has travelled once around the
wire loop:
• and, EMF:
• Here v is the relative velocity, B: magnetic field, E:
Electric field, dl: the integration over the wire and q:
the total charge of the particule (electron).
Kirchhoff's circuit laws
• Kirchhoff's circuit laws are two approximate
equalities that deal with the current and potential
difference (commonly known as voltage) in electrical
circuits. They were first described in 1845 by Gustav
Kirchhoff. This generalized the work of Georg Ohm
and preceded the work of Maxwell.
• Kirshoff current law, the principle of conservation of
electric charge implies that: At any node (junction) in
an electrical circuit, the sum of
currents flowing into that node
is equal to the sum of currents
flowing out of that node.
• Kirshoff voltage law: This law is based on one of the
Maxwell equations, namely the Maxwell-Faraday law
of induction, which states that the voltage drop
around any closed loop is equal to the rate-of-change
of the flux threading the loop.
Element types in an electrical circuit
• Passive Elements:
– Resistance ,Capacitance ,inductance. The components
that consume electrical energy or the components
that are incapable of power gain.
• Active Elements:
– Transistors, Batteries, diodes. The components that
produce electrical energy or components that can
inject power into a circuit.
• Electromechanical Elements:
– Electrical motors, MEMS devices, Ultrasonic
transducers