Direct Electric Current... - Lecture 10 Flashcards
Define the term ELECTRIC CURRENT
Electric current describes the directional movement of electric charge.
Define the term CURRENT
Current is the amount of charge which flows through the conductor per unit of time
I = dq / dt
measured in ampere, A
Define the term CURRENT DENSITY
Current density is the current per unit cross-sectional area of the conductor
j= dI / dS
j= zenv
What are the prerequisites for the generation of electric current?
- The availability of free electric charges in the conductor
- A voltage applied between the ends of the conductor
Define the term ELECTROMOTIVE FORCE
Electromotive Force is the work of the external agent for moving a unit positive charge along the conductor.
The conductance and the resistance of the conductor are determined by?
- The length L of the conductor
- The cross-sectional area S of the conductor
- The material of the conductor
G= y S/L R= p S/L
Describe Ohm’s law
The current I flowing through a conductor is directly proportional to the applied voltage u
I= Gu
G= conductance of the conductor (unit: siemens; s)
R= 1/G ; resistance if the conductor (unit: ohm )
Define the term CONDUCTIVITY y
Conductivity is the conductance of a conductor with cross-sectional are 1m^2 and length 1m.
Define the term RESISTIVITY p
Resistivity is the resistance of a conductor with cross-sectional are 1m^2 and length 1m.
p= 1/y
Define the term POLAR MOLECULES
The positive and negative charges are separated in spaces.
Eg: water; inorganic salts and acids…
Describe the solution of substances with polar molecules
The positively-charged ends of the polar molecules of the solvent are attracted by the negatively-charged ends of the polar molecules of the solute and vice versa.
Define the term DISSOCIATION
Dissociation is the splitting of neutral molecules into ions.
Define the term SOLVATION
The ions obtained by the dissociation of the solute are surrounded by the polar solvent molecules.
Ion diameters
The solvation increases the effective diameters of irons.
The number of solvent molecules surrounding an ion depends on temperature (more intense at higher temperatures).
Define the term RECOMBINATION (association)
It describes the bonding of ions with opposite charges in the solution producing neutral molecules.
Define the term DISSOCIATION CONSTANT (alpha)
The dissociation constant (alpha) is the ratio of dissociated molecules to the total number of molecules.
alpha = n+/c = n-/c
c=the number of dissolved molecules per unit (concentration)
n+/- = the number of positive/negative charged ions per unit volume
On what depends the dissociation constant (alpha)?
- Relative permittivity of the solvent
- dipole moment of the solute molecules
- solute concentration
- Temperatur
Define the term ELECTROLYTES (ionic solutions)
Electrolytes are substances with ionic conductance.
Charge carriers are positive and negative ions
Define the term CHARGE MOBILITY u
Charge mobility u is the drift (constant) velocity of the charge per unit magnitude of the electric field.
u = V/E
Which is the formula for conductivity of electrolytes?
y = (alpha) cze (u+ + u-)
Conductivity y depends on?
- Concentration (directly and through (alpha))
- Temperature (through (alpha) and u)
- Type of electrolyte (through (alpha), u and z)
Describe the conductivity of biological tissue.
Proteins and lipids have low conductivity.
The ionic solutions have high ionic conductivity.
Eg:
blood/cerebrospinal liquid > high conductivity
bones/dry skin > low conductivity
Define the term RHEOGRAPHY
Rheography is a method for investigation of the supply of blood to organs by measuring their conductivity.
Conductivity of gases
A pure gas consist of neutral atoms and/or molecules. Gases do not contain free charge carriers and are dielectric.
