Resistance:
Electric current in a conductor consists of movement of electrons. When electrons flow through a material, they collide with other atomic particles and energy is lost in these collisions.
The energy lost per unit charge is the voltage drop across the material. The ratio of voltage drop to current is the resistance of the material.
Thus,
V = IR
Where, v= voltage drop, (v)
I=current, (A)
R=resistance (ohms,Ω)
Above equation is known as ohm's law which can be stated as under: "The potential difference between the ends of a conductor is equal to the product of its resistance and current."
The voltage and current may be constant or functions of time. Above Figure shows a schematic representation of resistance. V is the voltage drop in the direction of current or a voltage rise in the opposite direction to flow of current.
Capacitance:
Let us refer again to the elementary capacitor shown in below figure for a given battery voltage a definite number of electrons is attracted into the bottom plate and the same number of electrons is driven out of the top plate of the capacitor. If the applied voltage is doubled, twice as many electrons get accumulated on the bottom plate and get driven out from top plate. The amount of charge is directly proportional in the voltage.
Q = Cv
The constant of proportionality C is called the capacitance of the capacitor.
The SI unit of capacitance is Farad (F). The Farad is the capacitance of a capacitor that store a charge of 1 Coulomb when the potential difference between its terminals is 1 volt. Farad represents a very large value of capacitance. Therefore the terms µF (Micro Farad) and pF ( pico farad) are commonly used.
Inductance:
A statically induced e.m.f can be self induced too. Whenever the current through a coil changes the flux also changes. The change of flux induces an e.m.f in the coil. Thus a coil can introduce an e.m.f in itself when the current through it changes. This property of the coil is known as inductance. The self-induced e.m.f can be written as
Where e is the induced e.m.f and di/dt is the rate of change of current. The coefficient L is called the self-inductance or simply inductance.
The SI unit of inductance is Henry (symbol H). The inductance of a coil is 1 Henry if an e.m.f of 1 volt is induced in it by a current changing at the rate of 1 ampere per second. It is evident that every coil or even a single conductors has self inductance. However it comes into play only when the current through the coil (or conductor) changes.
By Len'z law this induced e.m.f is in a direction so as to oppose the external e.m.f which is draining current through the coil.
In applying above equation, the induced e.m.f can be written as a voltage drop (from a to b) or as a voltage rise (from b to a) as seen in figure below.
When it is expressed as a voltage drop eab,we write
When this e.m.f is written as a voltage rise, it is necessary to add a negative sign. Therefore
In written circuit equations, the former representation is always preferred and the induced e.m.f is written, without the negative sign, as
Electric current in a conductor consists of movement of electrons. When electrons flow through a material, they collide with other atomic particles and energy is lost in these collisions.
The energy lost per unit charge is the voltage drop across the material. The ratio of voltage drop to current is the resistance of the material.
Thus,
V = IR
Where, v= voltage drop, (v)
I=current, (A)
R=resistance (ohms,Ω)
Above equation is known as ohm's law which can be stated as under: "The potential difference between the ends of a conductor is equal to the product of its resistance and current."
The voltage and current may be constant or functions of time. Above Figure shows a schematic representation of resistance. V is the voltage drop in the direction of current or a voltage rise in the opposite direction to flow of current.
Capacitance:
Let us refer again to the elementary capacitor shown in below figure for a given battery voltage a definite number of electrons is attracted into the bottom plate and the same number of electrons is driven out of the top plate of the capacitor. If the applied voltage is doubled, twice as many electrons get accumulated on the bottom plate and get driven out from top plate. The amount of charge is directly proportional in the voltage.
Q = Cv
The constant of proportionality C is called the capacitance of the capacitor.
The SI unit of capacitance is Farad (F). The Farad is the capacitance of a capacitor that store a charge of 1 Coulomb when the potential difference between its terminals is 1 volt. Farad represents a very large value of capacitance. Therefore the terms µF (Micro Farad) and pF ( pico farad) are commonly used.
Inductance:
A statically induced e.m.f can be self induced too. Whenever the current through a coil changes the flux also changes. The change of flux induces an e.m.f in the coil. Thus a coil can introduce an e.m.f in itself when the current through it changes. This property of the coil is known as inductance. The self-induced e.m.f can be written as
Where e is the induced e.m.f and di/dt is the rate of change of current. The coefficient L is called the self-inductance or simply inductance.
The SI unit of inductance is Henry (symbol H). The inductance of a coil is 1 Henry if an e.m.f of 1 volt is induced in it by a current changing at the rate of 1 ampere per second. It is evident that every coil or even a single conductors has self inductance. However it comes into play only when the current through the coil (or conductor) changes.
By Len'z law this induced e.m.f is in a direction so as to oppose the external e.m.f which is draining current through the coil.
In applying above equation, the induced e.m.f can be written as a voltage drop (from a to b) or as a voltage rise (from b to a) as seen in figure below.
When this e.m.f is written as a voltage rise, it is necessary to add a negative sign. Therefore
In written circuit equations, the former representation is always preferred and the induced e.m.f is written, without the negative sign, as
0 on: "Resistance, Capacitance & Inductance"