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Physics RCOA > Electrics & Diathermy > Flashcards

Electrics & Diathermy Flashcards

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1
Q

What is the oscillation of the UK mains supply?

A

-340 - +340
240V is the root mean voltage

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2
Q

What is Ohm’s law?

A

For a given voltage the current that flows is inversely proportional to the resistance of the path

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3
Q

What does current depend on?

A
  • How much current flows
  • Type of current
  • Frequency of current
  • Current pathway
  • Current density
  • Duration of current flow
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4
Q

How is the amount of current flowing determined?

A

Ohm’s Law

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5
Q

What is the equation for 1) Power, 2) Voltage

A

1) P = I(sq)R
2) V = IR

I = current

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6
Q

What are the effects of electrocution at different amps?

A

1-5 = tingling
5-10 = Pain
15 = No letting go
50 = Resp arrest
100 = VF

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7
Q

How is electrical equipment classified?

A

According to means by which it provides electrical safety
- Class 1
- Class 2
- Class 3

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8
Q

Describe class 1 equipment

A
  • Accessible conductive parts (casing) are connected to earth by earth wire
  • Maintains exposed metalwork at 0 potential
  • Provides low resistance path for current to return to local substation in event of fault
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9
Q

What happens if a fault occurs in class 1 equipment?

A
  • If live component touches casing this also becomes live
  • Current would flow both through the circuit & through the earth back to the substation
  • If you touched the casing current would also flow through you
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10
Q

How is a class 1 electrocution prevented?

A

Earth has very low resistance so in a fault larger current flows along this.
Total current flow increases causing fuse to blow & breaking the circuit

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11
Q

Describe class 2 equipment

A
  • Protected by double insulation
  • Minimal chance person could come into contact with faulty live component so no earth
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12
Q

Describe a class 3 component

A
  • Powered internally by a battery/SELV
  • Also known as a floating circuit
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13
Q

What is the difference between micro & macroshock?

A

MICRO: Skin is breached or aberrant currents delivered directly to the myocardium
MACRO: Current flows from intact skin to skin

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14
Q

What is the risk of micros jock induced ventricular arrhythmias based on?

A
  • Site of stimulation
  • Area of stimulation
  • Risk increases the longer the current passes
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15
Q

When might equipment predispose patients to microshock?

A
  • Currents can be delivered to myocardium via saline filled CVCs/pacing wires/oesophageal dopplers
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16
Q

How is a floating circuit separated from the mains supply?

A

Isolating transformer

17
Q

What does a transformer do?

A

Transfer power by their magnetic field
No direct electrical connection

18
Q

How can you get electrocuted in a floating circuit?

A

Would have to be part of the circuit that allows current to flow back to the substation

19
Q

What are the 2 types of circuit breakers?

A
  • Voltage operated: Detect rise in potential difference between protected metalwork & distant earth reference electrode. This isolates the downstream equipment from the mains.
  • Current operated: Compare current passing down the live wire & returning neutral wire (should be equal).
20
Q

How do circuit breakers work?

A

Disconnect the power supply from a piece of faulty equipment when current flows down the earth wire

21
Q

What are the 2 types of diathermy?

A
  • Monopolar: Small active electrode at site of surgery relative to ground
  • Bipolar: 2 electrodes to create local circuit.
21
Q

Why are high frequency currents used in diathermy?

A

Minimise the risk of inducing dysarrhythmias

22
Q

What is the heating effect proportional/inversely to?

A

P: The square of the current
I: The area which it passes

23
Q

In monopolar describe the properties of the active electrode

A
  • Small contact area
  • High current density
  • High resistance
  • Large heating effect
24
Q

Which type of diathermy causes higher risk of arrhythmias?

A

Monopolar

25
Q

In monopolar describe the properties of the ground plate

A
  • Large contact area
  • Low current density
  • Low resistance
  • Low heating effect
26
Q

Which uses lower power monopolar or bipolar?

A

Bipolar

27
Q

What microscopic effects does diathermy cause?

A
  • Coagulation - At higher temps/current density, proteins denature
  • Desiccation - At lower temps/current density, cellular detail preserved
28
Q

What macroscopic effects does diathermy cause?

A
  • Vaporisation - At high current density & cutting of tissue
  • Widespread superficial tissue destruction
29
Q

How are the macro & microscopic diathermy effects achieved?

A
  • Cutting: Continuous high frequency causes vaporisation
  • Coagulation: Modulated frequency, allows time for tissue to cool in between
  • Blended: A blend of above 2

Physics RCOA (9 decks)

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