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Medical Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is electricity?

A

Electricity is an apparent force in nature that exists whenever there is a net electrical charge between any two objects.

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2
Q

What is electric charge?

A

Electric charge is a physical property of elementary particles of an atom.

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3
Q

What happens to the magnitude of charge?

A

Even though charge can be both positive and negative, the magnitude of charge is always quantized.

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4
Q

What is the SI unit of charge?

A

the coulomb (C)

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5
Q

What happens when the number of protons and electrons is equal?

A

protons = positively charged
electrons = negatively charged
if proton # = electron # then there is NO ELECTRICAL FORCE, as there is NO NET CHARGE.

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6
Q

Whaat happens to electric charge? Is it created? Is it destroyed?

A

Electrical charge is conserved.
Charge cannot be created or destroyed.

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7
Q

Explain Coulomb’s law. What does it describe?

A

Coulomb’s law describes the electrostatic force F between two charged particles q1 and q2 separated by distance r.

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8
Q

What is the permittivity constant?

A

the permittivity constant describes the medium (vacuum, air, water).

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9
Q

What is electric field? What is its unit?

A

Electric field defines the electric force exerted on a positive unit charge positioned within any given space.
Described by the letter “E”.

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10
Q

What is “Potential Energy”?

A

Potential energy is the capacity for doing work in relation to the position or configuration.

eg. if a positive charge is fixed at some point in space, any other positive charge, which is brought close to it, will experience a repulsive force and will therefore have potential energy.

Potential energy defines the amount of work required to move a charge q from an infinite distance to its final position within electric field E.

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11
Q

What are the units for “Potential Energy”?

A

W(p)

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12
Q

What is electric potential?

A

Electric potential at any point of electrostatic field E is defined as the potential energy Wp per unit charge at the point.

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13
Q

What does the electrostatic potential difference represent?

A

The work required to move a unit charge from one point to another.

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14
Q

What are equipotential lines?

A
  • lines that havev the same value at all points of the line
  • they are always perpendicular to electric field lines
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15
Q

What are the units of potential and potential difference?

A

Volts (V)
- voltage is measured.

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16
Q

What is electrophoresis?

A

The term electrophoresis describes the transport of charged macromolecules (proteins or DNA) through electrolyte under an applied voltage.

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17
Q

What is electrophoresis used for?

A

It is used to characterize various objects ranging from bacteria or viruses to globular proteins or DNA.

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18
Q

Why is electrophoresis of various objects possible?

A

It is possible due to the objects’ net electric charge.

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19
Q

How are proteins seperated?

A

Particles (or proteins) having different charges will travel different distances during given time and will be separated from each other.

20
Q

What is an electric dipole?

A

An electric dipole is a system of two equal and opposite point charges separated by a small distance.

21
Q

What is the dipole axis?

A

The extended straight line joining the two point charges in a dipole.

22
Q

What is an electric current?

A
  • when charged particles move
  • there is net flow of charge across any area
23
Q

What is the definition of an electric current?

A

Current across the area is defined as the net charge transferred across the area per unit time.

24
Q

What is the sign for current?

A

I

25
Q

What is the symbol for charge?

A

q

26
Q

What is the unit for current?

A

Ampere (A)

27
Q

What is an alternating current?

A

When direction of charge flow changes from moment to moment.

28
Q

What is pulse current?

A

When current strength changes during time.

29
Q

What is the current density? What are its symbol.

A

Current per unit cross-sectional area.
Symbol is J.

30
Q

How is charge transferred in conductors?

A

transferred by electrons.

31
Q

What is electrophoretic mobility (of ions)? What does it depend on?

A

Electrophoretic mobility is defined as the velocity of electric particle under the unit electric field.

Mobility depends on electric charge, size of the ion and viscosity of the solution.

32
Q

Explain the differences in conductance of electric currents in the human organism. Which part of

A

Various tissues of living organism have different conductance to the electric current.

good conductance: organic fluids containing dissolved ions
- blood,
- spinal liquid,
- urine.

Medium conductance:
- internal organs
- muscle tissues.

Low conductance:
- bones
- dry skin

33
Q

What is impedance? What is its symbol?

A

The total resistance to the current.
(Z)

34
Q

How are rheograms created?

A

Small alternating current (AC) of frequency 20-30 kHz is used.

35
Q

What does the severity of electric shock depend on?

A

The effect of a shock depends on:
- the path the current takes,
- the duration of shock,
- whether the current is ac or dc.
(ac has dependence on frequency)

36
Q

What are the unit of electric shock current?

A

mA

37
Q

How many mA is needed for different types of shock?

A

1- Threshold of sensation
5- Maximum harmless current
10-20- Onset of sustained muscular contraction; can’t let go for duration of shock; contraction of chest muscles may stop breathing during shock (fatal if continued)
50- Onset of pain, heart still unaffected
100-300- Ventricular fibrillation possible; very often fatal
300- Onset of burns (thermal hazard); depends on concentration of current
6000 (6A)- Onset of sustained ventricular contraction and respiratory paralysis; both stop when shock is over; heartbeat often returns to normal

38
Q

Are values of electric shock the same to all genders?

A

No, female values are 60-80% of those for males.

39
Q

Why can’t people let go of electric wires during shock?

A

Somewhat higher currents can cause muscles to contract involuntarily.

The reason muscles contract is that nerves controlling muscles start sending electrical signals.

If you grasp the wire by your hand, hand will be unable to release the wire.

40
Q

What is the leading cause of death from electric shock?

A

The leading cause of death from electrical shock is ventricular fibrillation, an irregular, and uncoordinated beating of heart.

The victim dies from lack of blood circulation.

41
Q

How can one stop ventricular fibrillations?

A

Interestingly we can stop ventricular fibrillation passing much higher current through the heart.

42
Q

What is the severity of shock dependent on?

A

severity of shock depends on current and not directly of voltage.

43
Q

What is the resistance of the human body conductor?

A

Combined resistance when dry is approximately 1500 Ohms.

Combined resistance when wet is approximately 500 Ohms.

44
Q

What is the effect of frequency? How does the effect change at high vs low frequencies?

A

The body is most sensitive to electrical shock at frequencies close to 50- 60Hz.
(Possibly because it is similar to the firing frequency of many nerves)

Nerves and muscles of the body are less sensitive at both higher and lower frequencies.

The effects of high frequency shocks are mostly thermal. A large high frequency current may cause burns but is less likely to cause ventricular fibrillation. (Because of this high frequency currents are used in electrosurgery.)

45
Q

Explain electricity in gases.

A
  • CONDUCTANCE of ELECTRIC CURRENT of gas is equal to ZERO
  • PLASMA: at high temperatures, electrons are ‘stripped’ of atoms and molecules

PLASMA allows for the CONDUCTION of ELECTRICITY, causing a spark, arc, or lightning.

  • AEROIONS- ions in the air

negative ions- destroy harmful bacteria
positive ions- induce discomfort (depression, irritability, migranes, etc.)

46
Q

What is the type of therapy called that uses ions?

A

AEROIONOTHERAPY + ELECTROSTATIC SHOWER

Artificially generated aeroions can be used for treatment of patients or indoor spaces.

Sometimes so called “electrostatic shower” is used.
Aeroionization is provided by means of strong electric field generated by high voltage (up to 50kV).

47
Q

Explain how electric current travels through electrolytes.

A
  • through the movement of ions,
  • charge transfer,
  • positively charged ions (cations) move away from the anode,
  • negatively charged ions (anions) move away from the cathode.

Medical Physics (8 decks)

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