Electricity and Electrical Safety

Electricity results from ____?

mobile charges

Two types of charges

positive
negative

Law of Conservation of Electrical Charge

total amount of electric charge in the universe is constant

SI unit of electrical charge

coulomb (C)

the charge of one electron

-1.6x10^-19 C

the charge of one proton

1.6 x10^-19 C

Coulomb's Law

electric force between charged objects depends on the distance between the objects and the magnitude of the charges.
F=k x |q1||q2|/r^2

Coulomb's law provides only the ____ of the electrostatic force between two point charges, not the ____.

Coulomb's law provides only the MAGNITUDE of the electrostatic force between two point charges, not the DIRECTION

Electric field

all charges have an associated forced field that exerts the electric force on a test charge located at any point around a central charge

SI units of electric field

Newtons per coulomb (N/C)

Equation to calculate the force on a test charge if we know the magnitude of the test charge and the electric field strength

E= F/q0

if a charge at rest acquires kinetic energy but is held in place, the charge would have ____?

electric potential energy (U)

formula for electric potential energy

U=k qq0/r

SI unit for electric potential energy

Joule

Obtained by dividing the electric potential energy (U) by q0

Electric potential
V=U/q0=kxq/r

SI units for electric potential

energy per unit charge, volt (V)
1 joule/coulomb= 1xJ/C= 1 volt

The amount of charge flowing per unit time

Electric current (I)
I= change in Q/ change in time

SI unit for current

ampere (amp, A)
1 A= 1 coulomb/second= 1C/s

Charges move ______ in electrical conductors?

easily
metals are decent electrical conductors

Electrical insulators are materials in which charges ______?

cannot freely move
most insulators are nonmetallic
good insulators hold a significant static charge

Theory that states that atomic orbitals from individual atoms are added together to form molecular orbitals that extend over the entire molecule

Molecular orbital theory

The energy required to push electrons through a material is a measure of the _____ of the material

resistance

if a material has a constant resistance (R), the relationship between the potential difference V (voltage) and I (current) is given by ______?

Ohm's Law
V=IR or R=V/I

Ohm's law correlates ______?

flow of electricity, applied electrical pressure, and the resistance to flow

Ohm's law and SI units

resistance=R=V/I= volt/ampere=V/A

A volt divided by an ampere is called an _____?

ohm
1ohm=1V/A

Conductance (G)

Reciprocal of resistance
G=1/R
measured in Siemens (S) or mho

Clinical application of Ohm's law

Pressure=flow x resistance
MAP= CO x SVR

In what kind of circuit does current flow in one direction only and commonly uses batteries?

direct current (DC) circuit

In what kind of circuit does current periodically change direction and generally uses a wall outlet or AC generator?

Alternating current (AC) circuit

How do you find the equivalent resistance in a series circuit?

Total R= R1 + R2 + R3...etc

What's an example of a parallel circuit?

household circuits. Electricity can run through any individual appliance without needing every appliance to be turned on in order to complete the circuit

How do you find the equivalent resistance in a parallel circuit?

1/Req= 1/R1 + 1/R2 + 1/R3....etc

Electrical power

A change in electric potential energy results when a charge ?Q moves across a potential difference V
?U = ?QV

Since the power P is the rate at which energy is expended or consumed, we can say...

P= IV

the SI unit of power

the Watt (W)

1 watt is related to an ampere and a volt by

1 watt= 1 ampere x volt

in a resistor where I= V/R, the power can be expressed as

P=IV= I(IR)= I^2R

Electrical energy

a power unit multiplied by a time unit gives an energy unit
energy= power x time
kWh

What has the ability to control the conductivity by adding small amounts of impurities called doping agents?

Semiconductors

electron poor material composed of silicon doped with something like boron (has one less valence electron)

p-type (positive) semiconductor

electron rich material composed of silicon doped with something like arsenic (has an additional valence electron)

n-type semiconductors

circuit elements that have a large conductance in one direction and smaller in the opposite direction

diodes

Diodes are made by_____?

having p-type and n-type regions next to each other within a single crystal of silicon, called a pn junction.

______ biased if a voltage is applied so the n-region is biased negative compared to the p-region

Forward
holes and electrons move toward the pn junction.
If kept biased, the DC power supply will continue to provide electrons to the n-region and produce holes in the p-region. These electrons and holes will move toward the junction and annihilate.

is annihilation exothermic or endothermic?

exothermic and the energy is released as a photon of light

______ biased if the polarity of the DC power supply is reversed

Reverse
holes and electrons migrate away from the pn junction, creating a volume called a depletion region, with very few charges.
Resistance to current flow is very high compared to forward bias

Why are diodes considered nonohmic?

The current versus voltage relationship is nonlinear

Triodes

made from two closely situated pn junctions
AKA transistors, a circuit element useful for amplifying or switching currents.

Joule (U)

electrical potential energy

voltage (V)

potential difference between two points of a conductor; Si units for electric potential are energy per unit charge, which is a volt

current (I)

The amount of charge flowing per unit time; SI unit amperes

Resistance (R)

measure of how difficult the current flow through the conductor is, measured in ohms

Conductance (G)

Reciprocal of resistance; measure in Siemens (S) or mhos

Power (P)

SI unit of power is the watt (W), which is related to an ampere and a volt

Ohm's law

V=IR

Spectroscopy

The study of the properties of light that depend on wavelength.

Different colors have different wavelengths. Different wave lengths have different ______?

energies

When does light interact with matter?

When the energy of a photon exactly matches the difference in energy between two electron energy levels

What is the percent transmittance (%T)

Percentage of light that passes through a sample

How does spectroscopy work?

The detector in a spectrometer measures the intensity, or number of photons per second per unit area, of the light before it encounters the sample (I0) and after (I)
T= I/I0

The amount of light absorbed by the sample, the absorbance (A) is related to T by:

A=-log(T)=2-log(%T)
absorbance has no units

Examples of spectroscopy

pulse oximeter
blood work panel analysis

Beer's Law- what 3 factors affect how much light is absorbed by the sample?

absorptivity (A)- describes the likelihood that photon will excite the molecule, and is a constant for each substance at a given wavelength
greater concentration (C) of the analyte increases the change that photon will encounter a molecule with which to i

Beer's law is strictly true when _____?

the analyte concentration is zero

the sensation and muscular spasm caused by an electric current passing through the body

Electrical shock

This occurs when a relatively large amount of current flows through an individual, potentially resulting in injury or death

Macroshock

This occurs when a relatively minor current is delivered directly to the heart

Microshock

contains a thin metal strip that melts if the current exceed the rated value

fuse

made with a switch and a strip composed of two metals

circuit breaker

Designed to immediately disrupt the current in a circuit if an imbalance between the two currents is detected

ground fault circuit interrupter (GFCI)

Isolation transformer

consists of a primary circuit connected to an AC power source and a secondary circuit, each with coils wrapped around a common iron core

Designed to measure the impedance to ground of both lines in an isolated underground circuit

Line isolation monitors

conductivity of tendons, bone, fat

high

conductivity of dry skin

intermediate

conductivity of nerve, muscle, blood, mucous membrane

low

injury severity depends on

tissue resistance (R)
current (I)
potential difference (V)
current density, frequency, pathway, and duration

Frequency in OR

60Hz

vertical pathway

if the current passes though the heart causing muscle damage

horizontal pathway

If it disturbs electrical conduction pathway

1 mA

tingling pain

5 mA

pain

15 mA

tonic muscle contraction/pain

50 mA

respiratory tonic muscle contraction/resp. arrest

70-100 mA

V fib/ cardiac arrhythmias/ local burns

1000 mA

extensive burning/ charring

direct current leads to

single muscle spasm
throws from source
blunt mechanical trauma
heart disturbances

alternating current induces

tetany
flexor contraction
local sweating

Electrosurgery

provides hemostasis by burning blood vessels via an electrical current discharged from the machine to the patient.
electro surgical unit (ESU)
electrocautery
bovie

Electrosurgery current and volts

high frequency current 0.3-2 MHz
up to 3000 volts

Three elements that increase risk of fire

fuel or combustible material
heat or ignition source
oxygen