8. Electricity Flashcards
Resistors in parallel
R1xR2/R1+R2
or
1/ RT = 1/ R1 + 1/ R2
across from each other
Resistors in series
Rtotal = R1 + R2 +R3
side by side
Alternating current (AC) Describe Amplutude change w/ Shapep one cylce mains freq - & volts
is a flow of current along a conductor that constantly changes direction. The amplitude of the current changes with time or the angle of rotation (θ). The shape of one full cycle is 360° (or 2π) is a sinusoid. Mains electricity has a frequency of 50 Hz and the current driven by a potential difference of 240 volts.
Direct current DC
is a flow of current along a conductor in one direction only. Batteries or cells supply DC.
Full wave rectifier:
is composed of what
what do these do
why is it useful
Ectrical component that is composed of four diodes.
Diodes - semiconductor materials that can allow current to flow in one direction and block current in the opposite direction. Alternating current (AC) passing through this arrangement of diodes produces direct current (DC).
Transformers:
what use for
what element is important
diffrence between what
whats the use
Electrical component w/ iron core - transfers energy between 2/+ circuits by electromagnetic induction.
The iron core is used to concentrate the magnetic flux. A typical transformer will have a primary (input) wire coil and a secondary (output) wire coil.
Difference between the input and output voltage will depend on the differences in the number of turns of the wire between the primary and secondary coils. Transformers are used to isolate circuits, change impedance and alter voltage output.
Transformers Do not convert AC to DC.
Capacitor:
What is it
What does it consist of
How is it measured
Is an electrical component that stores charge in the form of an electrostatic field and is the key component of a cardiac defibrillator.
It consists of two metal plates separated by insulator (dielectric).
Capacitance is measured in farads (typically μF, pF or nF).
1 farad = potential difference of 1 volt across plates.
Capacitors are used to ‘smooth out’ rectified AC voltage to produce battery-like DC voltage. Capacitors do not directly convert AC to DC.
1 farad =
potential difference of 1 volt across plates.
the SI unit of electrical capacitance, equal to the capacitance of a capacitor in which one coulomb of charge causes a potential difference of one volt.
Inductor:
In its simplest form is a wire, often coiled around an iron core. An electromagnetic force generated when a potential difference is applied across the wire produces a ‘back’ electromotive force (emf) sufficient to slow the passage of electrons and therefore current.
Step-down transformer:
Whats the components
what does it do
Has more turns of wire in the primary coil than the secondary coil.
The induced voltage by electromagnetic induction is smaller in the secondary coil.
For example, the input might be 240 volts AC but the output only 12 volts.
Step-up transformer:
There are more turns of wire in the secondary coil than the primary coil. The induced voltage is larger in the secondary coil. This type of transformer is used in the defibrillator to increase the voltage input of 240 volts to 6000 volts to enable the charging of a capacitor.
what do we feel / sequlae of
1 mA 5 mA 15 mA 50 mA 75 mA
tingling pain pain Tonic muscular contraction Respiratory muscle paralysis ventricular fibrillation.
Electrical safety classes
I
II
III
I. Basic protection
II. Double insulated
III. Safety extra low voltage.
Microshock is a
Microshock is a small leakage current that can result in harm because of direct connection to the heart via transvenous lines or wires, bypassing the impedance of the skin can lead to ventricular fibrillation. Microshock current of 100 μA is sufficient to cause VF.
type CF equipments protect against microshock as they allow leakage currents of 0.05 mA per electrode for class I equipment and 0.01 mA for class II
Equipotentiality is a safety feature when
metalwork increases to the same potential so that current is unable to flow.
functional earth on medical devices
proper functioning and not a safety feature. The functional earth can be used for interference suppression. It is a low-impedance current path between the circuitry and earth. They can be found on antennae. A protective earth on medical devices is a safety feature of medical devices and aims to prevent electrocution.
OHMs law
potential difference equals current multiplied by resistance
V = I x R (volt = i Curr x Resist Ohm)
Defibrillator can be used w/
BF and CF equipment have to be modified so that they can be used in conjunction with a defibrillator.
Subclass I & II safety B BF CF
B (Body)
aximal permissible leakage current is 500 µA. This current is large enough to cause tingling of the skin but not cause significant injury. It is however large enough to cause microshock. Defibrillators should not be used with this type of equipment.
BF (Body Floating
BF (Body Floating) - These devices have an isolating capacitor or transformer. These separate the secondary circuit form the earth. Permissible leakage current is the same as that of type B equipment
CF (Cardiac Floating)
CF (Cardiac Floating) - the maximum permissible current leakage in the event of a single fault is 50 microA and is the type of equipment least likely to cause microshock.
Calculate resistors in series
Potential difference (V) = current (I) x resistance (Ω).
Rearranging the equation:
I = V/R1 + R2
Inductor
What is it
How to increase conductance
What opposes driving voltage
Time constant
Volt proport
Voltage change proportion to
Coil of wire. It has the capacity to store energy in the form of a magnetic field
Winding a wire around an iron core increases the “inductance” of the wire.
Induced voltage opposes the driving voltage, the so-called “back-em
time constant of a circuit containing L and R = L/R, where R is resistance.
Voltage (V) is proportional to the rate of change of current (V = L·di/dt)
Proport to frequency
Capacitance - meaure
what is the measure
what does one of them eqaul
ability hold charge
measured in farad
1f
-1v is potential difference acrros plates -
charge of 1columb held by plates
1 unit of charge = amt electicity equiv to 6.24 x 10^18
charge = capaci(farad) X Volts (potent diff)
Capacitor has 2 conducting paltes seperated insulator
