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Sarah's Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Electrical current definition and units

A

Flow of electrical charge

1 ampere = 1 coulomb / second

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2
Q

Electrical voltage definition

Voltage units

A

Potential difference between two points to drive electrons around a circuit

Volts = Joules/ Coulomb

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3
Q

What is a coulomb

A

Unit of charge (Q)

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4
Q

What is conductance what is its units

A

The ability of the material to allow the flow of electrical charge

Measured in sieman

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5
Q

What is resistance

A

The ability of a material to resist the flow of charge

Measured in Ohms

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6
Q

Ohms law

A

Resistance = voltage / current

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7
Q

Equation for power (work per second)

A

Power (watts) = voltage x current

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8
Q

What is a Wheatstone bridge?

A

Two voltage dividers in parallel.
Allows signal common to both arms to be undetected and AMPLIFIES biological signal.
Measuring resistor attached to a strain gauge transducer which changes resistance with change in pressure.
Voltmeter detects difference between sum total of resistance between the two ciruits.
Fourier analysis then amplifies and plots waveform.

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9
Q

What is a transformer

A

Device which transfers electrical energy from one circuit to another using electromagnetic induction.
Can be step up or step down depending on number of coils in each circuit

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10
Q

What is a diode

A

Allow current to flow in one direction only

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11
Q

What is a transistor

A

Components which open and close to allow movement of electrical current in response to a control voltage

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12
Q

What is common mode rejection ratio

A

An amplifier which neutralises signals common to both inverting and non inverting inputs. Only amplifies input voltage difference. High ratio means good quality op amp.

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13
Q

What is a transducer, how do they work

A

Change one type of energy into another.

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14
Q

What is a capacitor

A

A device which stores electrical charge.

Made of two conducting plates sandwiching a non conducting dielectric

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15
Q

What is one farad

A

The ability for a capacitor to store one coulomb of charge when one volt is applied across it.

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16
Q

What is inductance

A

Opposes the flow of current by creating an electromotive force.
This repels electrons and slows flow of current.

17
Q

Factors affecting thoracic impedence

A

Stroke volume (increases)
Ventilation (increases)
Pulmonary oedema (decreases)

18
Q

Voltage equation

A

V = IR

19
Q

The energy required to move one coulomb of charge between two points in a cicuit.

A

Electromotive force

20
Q

Why is an op amp helpful

A

Op-amps are incorporated into electrical circuits with many other components to achieve a desired signal output from a recorded biological potential

21
Q

What elements are required to process biological signals to electrical ones

A

Transducer, amplifier, filter, convert analogue to digital, store and display

22
Q

What happens if the analogue sampling rate is too low

How does analogue conversion work

A

Digitized waveform is a poor representation of the frequency and magnitude of the biological signal.

Sampling the analogue sine wave at the chosen frequency gives a digital staircase waveform which is smoothed out by low pass filtering.

23
Q

Energy stored by capacitor equation

Capacitance of defib

A

E = 1/2 CV²

32 microfarads

24
Q

Capacitance equation

A

C = Q/ V

25
Q

Work equation for electricity

A

W = VQ

26
Q

Describe how a defib works

A

Charging circuit - voltage applied to circuit through step up transformer. Current delivered to a capacitor creating a potential difference. Since W = VQ, as voltage increases work must increase to store charge. This slows down exponentially as it reaches a maximum.

Patient circuit - switch moves to allow capacitor to discharge until voltage falls to zero exponentially. An inductor increases the time over which the energy is discharged.

27
Q

What is fourier analysis

A

Analyses sine wave via its component parts

28
Q

Force equation for magents

A

F = QUB (where B is magnetic flux density, measured in tesla)

29
Q

How do transformers work

A

Transfer electrical energy either step up or step down from one circuit to another by means of a magnetic field linking both circuits. Coils step copper around a steel core to minimise hysteresis loss. Only in AC.

30
Q

Current 1mA effect

A

tingling

31
Q

Current 5mA effect

A

pain

32
Q

Current 15-30mA effect

A

muscle contraction

33
Q

Current 50mA effect

A

Asphyxia

34
Q

Current 100mA effect

A

VF

35
Q

Features of class 1 electrical device

A

Mains powered
Earthed metal case
Fuse wire

36
Q

Features of class 2 electrical device

A

2x insulated
Unearthed

37
Q

Features of class 3 electrical device

A

Battery operated

Sarah's Physics (6 decks)

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