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Medical Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Constitution of Matter

A

constituted of electrically charged particles

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2
Q

What do electric charges create

A
  • electric field
  • they participate in electric interactions by electric forces
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3
Q

Electric Charge unit

A

measured in coloumbs(C)

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4
Q

how are the phenomena that occur in presence of electric fields described as

A

described by quantities such as an:

  • electric potential
  • voltage
  • electric field intensity
  • electric current strength
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5
Q

Electric potential

A

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.
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6
Q

Electric current

A

flow of electric charges

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7
Q

3 requirements for current to occur

A
  • free charged particles
  • conducting medium
  • electromotive force
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8
Q

Conducting media

A

can be solids, liquids, gases

  • charges can cross it freely
  • electric carriers in solid conductors are typically e-,
  • ions in liquids and gases
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9
Q

Electromotive force

A
  • any phenomenon/device which produces electric potential difference
  • maintains it during current propagation
  • voltage (V)
    e. g. alternating source - generators, direct current source - batteries
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10
Q

Free charge

A
  • electric charge which can move freely
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11
Q

Electric current strength

A

total charge moving per unit time

I = Q/t

measured in Ampere

1 Ampere equals to 1 Coulomb passing per second

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12
Q

3 types of media in terms of their electric properties

A

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
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13
Q

Solid conductors

A

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

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14
Q

Semiconductors

A
  • 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
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15
Q

Two main electric current types

A

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
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16
Q

Main parameters of AC

A

frequency f

amplitude I0 (PEAK VALUE)

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17
Q

Time relation of AC

A

I = I0 Sin (time x freq. x 2π

T= 1/freq,

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18
Q

Direct currents

A

A) Constant Current

  • constant value

B) Pulse Direct Current

  • varying amplitude but constant direction
19
Q

Fundamental qualities in the reaction of any conducting medium to electric currents

A
  • electrical resistance
  • electrical capacitance
  • inductivity
  • each quantity can be considered as a particular component of en electrical circuit
20
Q

Electrical resistance

A

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

21
Q

Ohm’s law

A
  • 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

22
Q

Capacitance

A
  • 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

23
Q

Capacity resistance

A
  • opposing the alternating current passing through the capacitor

Xc = 1/ωC

ω - electric current circular freq.

24
Q

Transformation of energy of current passing through capacitor

A

in capacitor, the energy of the current passing is transformed to electric field

25
Q

Inductance, L

A

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)

26
Q

Inductive resistance, XL

A

the reaction of an inductive component to the propagating electric current

= ωL

27
Q

Transformation of the energy of the current in an electric coil

A

Within an electric coil the energy of the current passing is transformed to magnetic field

28
Q

The resistance of a complex electric circuit (consisting of all types of components)

A

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

29
Q

Rheoencephalography

A
  • 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
30
Q

What are these curves showing?

A
  • in Rheoencephalography
  • The curves obtained reflect the rate of blood supply and depicted disorders related to elasticity lose and increase of resistance.
31
Q

How is electric current in liquids and gases carried

A

by ions

32
Q

Electrolyte

A
  • any substance containing free ions that make the substance electrically conductive
  • most typical - ionic solutions
33
Q

Electrolyte Dissociation

A

spontaneous conversion of substance molecules into ions as result of interaction with the molecules of solvent (e.g. NaCl in water’s polarity)

34
Q

Electorlyte dissociation in NaCl (aq)

A

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.

35
Q

Faraday’s law

A
  • 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

36
Q

Changing of Dielectric gases

A
  • insulating
  • normally gases are dielectric because they are built up of neutral atoms and molecules
  • passage of current is possible after preliminary ionisation
37
Q

Gas discharge

A
  • high voltage electric source and electrodes
  • used to ionise gases
38
Q

Radiation for dielectric gases

A
  • alpha, beta and gamma rays

-

39
Q

Primary ionisation

A
  • 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
40
Q

Aeroions

A

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
41
Q

Electrophoresis/Ionophoresis

A
  • 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
42
Q

Requirements of Electrophoresis

A
  • Drug dissociation (in water)
  • High permeability area of electrode placement
43
Q

Apex location

A
  • 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

Medical Physics (10 decks)

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