10) Electric Currents Flashcards
Electric current
Directional movement of electric charge
Measured in amps
I=dq/dt
Current density
J=di/ds
Current per unit cross sectional area of conductor
Current density 2
J=zenV
J=Di/ds = d^2q/dsdt
DRAWING
Prerequisites for the generation of electric current
Voltage applied between ends of conductor causing charge to move
Availability of free charge carries
Electromotive force
Work of external agent for moving a positive charge along the conductor
Conductance and resistance
G is conductance
R= 1/G resistance of conductor
I=GU
current = conductance x voltage
P=1/lander
Conductance and resistance 2
Determined by;
Length of conductor
Cross sectional area
Material of conductor
G=lander s/L
R= p L/s
Polar molecules
Positive and negative charges separated in space
Eg
Water
Salts
Solutions of substances with polar molecules
The positively charged end of s polar molecule will attract the negatively charged end of another polar molecule
Dissociation
The spiriting of neutral molecules into ions
Drawing
Solvation
The ions obtained by dissociation are surrounded by the polar solvent molecules
Ion diameter
The number of solvent molecules surrounding ion depends on temp
Recombination
Bonding of ions with opposite charges to produce neutral molecules
Dynamic eq is reached between dissociation and recombination
Dissociation constant
The ratio of dissociated molecules to the ratio of total number of molecules
Alpha = n+/c = n-/c
Number of ions
Number of dissolved molecules c
Depends on:
Solute conc
Temp
Electrolytes
Substances with ionic conductance has positive and negative
