Electricity Flashcards
Constitution of Matter
constituted of electrically charged particles
What do electric charges create
- electric field
- they participate in electric interactions by electric forces
Electric Charge unit
measured in coloumbs(C)
how are the phenomena that occur in presence of electric fields described as
described by quantities such as an:
- electric potential
- voltage
- electric field intensity
- electric current strength
Electric potential
electrostatic potential φ
- amount of electric potential energy that a unitary point electric charge possesses being located at certain point in space
- is equal to the work done by an electric field in carrying a unit positive charge from infinity to that point
- the amount of work needed to move a unit of charge from a reference point to a specific point inside the field without producing an acceleration. Typically, the reference point is the Earth or a point at infinity, although any point can be used.
Electric current
flow of electric charges
3 requirements for current to occur
- free charged particles
- conducting medium
- electromotive force
Conducting media
can be solids, liquids, gases
- charges can cross it freely
- electric carriers in solid conductors are typically e-,
- ions in liquids and gases
Electromotive force
- any phenomenon/device which produces electric potential difference
- maintains it during current propagation
- voltage (V)
e. g. alternating source - generators, direct current source - batteries
Free charge
- electric charge which can move freely
Electric current strength
total charge moving per unit time
I = Q/t
measured in Ampere
1 Ampere equals to 1 Coulomb passing per second
3 types of media in terms of their electric properties
conductors, semiconductors and non-conductors
difference is based on:
- quantum energy structure of particles of which the given material is composed of
- availability of free charges
- number of charges relating to environment
- physical condition
Solid conductors
e. g. metals - cooper and aluminum because of their good conductivity.
- characterised by high density of free charge carriers
- provides conduction of high magnitude current
Semiconductors
- electric properties strongly dependent on temperature, exposure to electric fields, light illumination and other physical agents
- heating up or illumination of semiconductors causes an increase of their conductivity
Two main electric current types
Direct current (DC)
- flows at certain direction, determined of emf action
- in metals, free e- move from -ve –> +ve electrode potential (pole)
Alternating current (AC)
- charge flux which alters its direction cyclically
- rate of their alteration determines the freq. of current
Main parameters of AC
frequency f
amplitude I0 (PEAK VALUE)
Time relation of AC
I = I0 Sin (time x freq. x 2π
T= 1/freq,
Direct currents
A) Constant Current
- constant value
B) Pulse Direct Current
- varying amplitude but constant direction
Fundamental qualities in the reaction of any conducting medium to electric currents
- electrical resistance
- electrical capacitance
- inductivity
- each quantity can be considered as a particular component of en electrical circuit
Electrical resistance
defined as the ratio of the voltage applied over the electric current which flows through it
- how much the medium opposes to the current passage
R= p (I/S)
ρ - specific resistance, feature of the material
l – length
S – cross section
Ohm’s law
- the size of an electric current is proportional to the voltage
- the size of an electric current is inverse proportional to the resistance
I = V/R
Capacitance
- measure for ability of a matter object (or component of electric circuit) to hold electrical charge
- Quantitatively, capacitance is measured by the electric charge needed to change the potential of the component by 1 volt:
C=Q/V
Capacity resistance
- opposing the alternating current passing through the capacitor
Xc = 1/ωC
ω - electric current circular freq.
Transformation of energy of current passing through capacitor
in capacitor, the energy of the current passing is transformed to electric field
Inductance, L
Inductance of a given electric component (coil) is evaluated by the emf generated within to oppose to the changes in current strength
EMF = -L△I/△t
L measured in Henry (H)
Inductive resistance, XL
the reaction of an inductive component to the propagating electric current
= ωL
Transformation of the energy of the current in an electric coil
Within an electric coil the energy of the current passing is transformed to magnetic field
The resistance of a complex electric circuit (consisting of all types of components)
requires impedance Z to be calculated
Z2 = R2 + (XL - Xc)2
measurement of body resistance/impedance is used in many diagnostic methods, such as Rheoencephalography
Rheoencephalography
- a techncique of continuous registration of cerebral blood flow
- an electronic device called a rheoencephalograph is used in rheoencephalography
- Electrodes are attached to the cranium at specific points on the head
- allows the device to continuously measure the electrical conductivity of the tissue located between the electrodes
What are these curves showing?
- in Rheoencephalography
- The curves obtained reflect the rate of blood supply and depicted disorders related to elasticity lose and increase of resistance.
How is electric current in liquids and gases carried
by ions
Electrolyte
- any substance containing free ions that make the substance electrically conductive
- most typical - ionic solutions
Electrolyte Dissociation
spontaneous conversion of substance molecules into ions as result of interaction with the molecules of solvent (e.g. NaCl in water’s polarity)
Electorlyte dissociation in NaCl (aq)
water molecules are polar dipoles. They surround Na and Cl ions and interact electrically with it. As consequence: the chemical bonds between Na and Cl are impaired off, Na and Cl ions are freely movable in the solution and solution becomes to electrolyte.
Faraday’s law
- external field applied to electrolyte - electric current flows carried by ions
- amount of flowing ionic substance is measured by FL
- used to measure drug dose introduced in electrophoresis.
m = M x Q/Z x F
m - mass of substance
M - molar mass
Q - charge of the given ion
Z - valence
F - faraday’s number
Changing of Dielectric gases
- insulating
- normally gases are dielectric because they are built up of neutral atoms and molecules
- passage of current is possible after preliminary ionisation
Gas discharge
- high voltage electric source and electrodes
- used to ionise gases
Radiation for dielectric gases
- alpha, beta and gamma rays
-
Primary ionisation
- Tearing off of an electron from neutral atom results in appearance of ion couple
- The propagation of electrons obtained can produce the secondary ionization
- Occurrence of the letter phenomenon needs an energy of 35 eV to be delivered.
- Repetition of this process and multiplication of ions obtained is base of gas-discharging devices.
- Ionization of gases is used for production of a light : the process of recombination of ions is supported with light emission
Aeroions
Two types:
- light -ve aeroions - favourable to human body, high conc. typical to mountains, forests, waterfalls
- heavy +ve aeroions - exert harmful influence upon the humans, high conc. typical to urban areas, city air
Electrophoresis/Ionophoresis
- method for local drug introduction through the skin by means of continuous directed electric current
- pulsed current also applied in order to achieve a better efficiency due to abolishment of polarisation secondary effects
- if anode is an active electrode, under it the positively charged pharmaceutical is impasted
- when electric circuit is switched on, the drug molecules are repulsed and penetrate in depth
Requirements of Electrophoresis
- Drug dissociation (in water)
- High permeability area of electrode placement
Apex location
- method for determining length of root canal of a tooth
- manually or with a mechanical canal instrument that passes a low intensity electric current through the tooth
- electrical characteristics of a tooth are measured and the exact position of the instrument in the tooth is determined
- when tool tip touched top of tooth - apical foramen reached
- when channel instrument is pulled out its length can be measured to determine the depth of root canal
