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final sensor 2024 c3 c4 Flashcards

1
Q

other names for potentiometer sensor

A

adjustable resistor

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2
Q

simplest type of displacement sensor involves..

A

the action of displacement in moving the wiper of a potentiometer

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3
Q

how potentiometric sensor works (2)

A

1- move the wiper of the potentiometer
2- the device then converts linear or angular motion into a changing resistance that may be converted directly to voltage and current signals

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4
Q

problems using potentiometric device (4)

A

1- mechanical wear (haus)
2-friction in the wiper action
3- limited resolution in the wire-wound units
4- high electronic noise

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5
Q

capacitive

A

the basic operation of a capacitive sensor can be seen from the familiar equation for a parallel-plate capacitor:

C= K(عo) (A/d)

K= dielectric constant
عo = permittivity = 8.85pF/m
A= plate common area
d= plate separation

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6
Q

How to change the capacity ? (3)

A

1- variation of the distance between the plates (d)
2- variation of the shared area of the plates (A)
3- variation of the dielectric constant (K)

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7
Q

Facts about capacitive sensor (2)

A
  • can detect any material with or without contact
  • can adjust the sensitivity to detect liquids or solids even through non-metallic tanks or vessels
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8
Q

A capacitor consists of ?

A

two plates generates an electrical between the plates when supplied with power.

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9
Q

inductive sensor(2)

A
  • an electronic device that can detect ferrous metal targets (iron metal based) like aluminium, brass and copper.
  • using non-ferrous metal target decreases an inductive sensors’ sensing range.
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10
Q

4 level sensors

A
  • mechanical
  • pressure
  • electrical
  • ultrasonic
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11
Q

tensile stress and tensile strain

A

stress = the effect of applied force
strain = the resulting deformation

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12
Q

5 formula
Tensile stress
Tensile strain
Compressional stress
Shear stress
Shear strain

A

tensile stress = F/A
F= applied force in N
A= cross- sectional area of the sample in m^2

tensile strain = Al/l
Al= change in length in m (in.)
l= original length in m (in.)

compressional stress = F/A

shear stress = F/A
shear strain = Ax/l
Ax= deformation in m
l= width of a sample in m

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13
Q

difference between compressional and tensile stress

A

the direction of the applied force and the polarity of the change in length.

tensile = tarik bagi panjang
compressional = penyek

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14
Q

the basic technique of strain gauge measurement

A

involves attaching (gluing using electrical glue wihich is not an insulator) a metal wire or foil to the element whose strain is to be measured

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15
Q

materials that are commonly used for an electrical glue

A

gold- expensive
silver/ copper- easy to oxidize

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16
Q

formula for gauge factor (GF)

A

GF = (AR/R)/strain

AR/R = fractional change in gauge resistance because of strain
strain = Al/l = fractional in length

GF semiconductor = (-)
GF metal = (+)

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17
Q

why high gauge factor is desirable

A

indicates a larger change in a resistance for a given strain and is easier to measure

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18
Q

construction for a metal strain gauge (5)

A

1- used in two forms, wire and foil (foil is more accurate)
2-very long
3-often made unidirectional (so it responds to strain in only one direction)
4- folding the material back and forth so we achieve a long length to provide high resistance
5- usually mounted on a paper backing that is bonded (using epoxy) to the element whose strain is to be measured. the most common value for SG resistance is 120 ohm

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19
Q

2 effects are critical in the signal-conditioning techniques used for SGs

A

1- fractional changes in resistance that require carefully designed resistance measurement circuits
2- the need to provide some compensation for temperature effects to eliminate masking changes in strain

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20
Q

solution to the effects of signal conditioning

A

bridge circuit (to avoid power dissipation)
- the sensitivity of the bridge circuit for detecting small changes in resistance is well known

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21
Q

advantages of dummy gauge / one-arm bridge (3)

A

-will not affect the output
-can provide the required temperature compensation
-to help active gauge with temperature problem

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22
Q

how dummy is mounted (3)

A

-in an insensitive orientation but in the same proximity as the active SG.
-both gauge change in resistance from temperature effects, but the dummy does not respond to a change in both strain gauges
-only the active SG responds to strain effects

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23
Q

Common application for strain gauges

A

measure deflections cantilever beam ( a beam that is supported at only one end and deflects when a load is applied)

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24
Q

how strain gauge measure the deflection of the cantilever beams

A

use a two arm bridge

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25
Q

how two arm bridge works in measuring the deflection of a cantilever beam (5)

A
  • one pair of active A1 and dummy D1 gauge is mounted on the top surface
  • the active gauge will experience tension with downward deflection of the beam, and its resistance will increase
  • the second pair, A2 and D2, are mounted on the bottom surface
  • the active gauge will experience compression with downward deflection and its resistance will decrease

A1 D1 - tensile
A2 D2 - compress

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26
Q

principle of semiconductor strain gauge (5)

A
  • the basic effect is a change of resistance with strain
  • in the case of a semiconductor, the resistivity also changes with strain, along with the physical dimensions
  • this is due to changes in electron and hole mobility with changes in crystal structure as strain is applied.
  • the net result is a much larger gauge factor than is possible with metal gauge
    -For semiconductor strain gauge, the GF is often negative (the resistance decreases when a tensile (stretching) stress is applied.
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27
Q

construction of semiconductor strain gauge (3)

A
  • physically appears as a band or strip of material with electrical connection
  • the gauge is either bonded directly onto the test element or id encapsulated, is attached by the encapsulation material.
  • these SGs also appear as IC assemblies in configurations used for other measurements
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28
Q

motion sensor

A

to measure the rate of change of position, location, or displacement of an object is occurring

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29
Q

4 types of motion

A
  • shock (accident)
  • rectilinear (pergerakan biasa)
    -angular (rotation)
  • vibration
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30
Q

rectilinear motion

A
  • characterized by velocity and acceleration which id composed of straight-line segment
  • example : car key
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31
Q

angular motion (3)

A
  • designed to measure only rotations about some axia
  • such devices cannot be used to measure the physical displacement of the whole shaft but only in rotation
  • example : the angular motion motion of the shaft of a motor
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32
Q

vibration motion

A

-random in both the frequency of periodic motion and the magnitude of displacements from equilibrium

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33
Q

shock motion

A
  • a special type of acceleration occurs when an object that may be in uniform motion or modestly accelerating is suddenly brought to rest, as in collision
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34
Q

cause of shock motion (2)

A
  • such phenomena are the result of very large accelerations or actually decelerations as when an object is dropped from some height onto a hard surface
    -typically on the order of milliseconds with peak accelerations over 500g
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35
Q

types of accelerometer

A
  • potentiometric
    -LVDT
    -variable reluctance
    -piezoelectric
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36
Q

accelerometer : potentiometric (3)

A
  • measures mass motion by attaching the spring mass to the wiper arm of the potentiometer
  • the mass position conveyed as a changing resistance
  • natural frequency is less than 30 Hz (limiting their application to steady state acceleration or low frequency vibration measurement)
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37
Q

accelerometer : LVDT (4)

A
  • measure mass displacement
  • the core itself is the seismic mass
  • displacements of the core are converted directly into a linearly proportional ac voltage
  • natural frequency of less than 80 Hz and commonly used for steady-state and low frequency vibration
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38
Q

accelerometer : variable reluctance (5)

A
  • the test mass is usually a permanent magnet
  • the measurement is made from the voltage induced in a surrounding coil as the magnetic mass move under the influence of an acceleration
  • used in vibration and shock studies only (has an output only when the mass is in motion)
    -natural frequency is typically less than 100Hz
    -often used in oil exploration to pick up the vibrations reflected from underground rock strata
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39
Q

Accelerometer : Piezoelectric (3)

A
  • When exposed to an acceleration, the test mass stresses the crystal by a force , resulting in a voltage generated across the crystal.
  • A measure of this voltage is then a measure of the acceleration. The crystal per se is a very high-impedance source, and thus requires a high-input impedance, low noise detector.
  • natural frequency may exceed 5 kHz, so
    that they can be used for vibration and shock
    measurements.
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40
Q

example of steady-state acceleration

A

stop-go motion of an automobile

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41
Q

steady state acceleration application (3)

A
  • measure of acceleration that vary in time but nonperiodic.
  • a good sensor
    1. adequate range to cover expected acceleration magnitudes
    2. a natural frequency sufficiently high that its period is shorter than the characteristic time span over which the measured acceleration changes.
  • by using electronic integrators, the basic accelerometer can provide both velocity and position information
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42
Q

Pressure Principles (3)

A

-the force per unit area that a fluid exerts on its surroundings.
- If every wall in the gas must have the same pressure in order for the gas to be fully enclosed.
- In a liquid, the pressure will vary, need not be enclosed

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43
Q

Static pressure (2)

A
  • For a fluid that is not moving in space, that is not being pumped through pipes or flowing through a channel.
  • The pressure in cases where no motion is occurring
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44
Q

Dynamic pressure

A
  • If a fluid is in motion, the pressure that it exerts on its surroundings depends on the motion.
  • Pressure can depend on flow, compressibility of the fluid and external force
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45
Q

types of pressure

A
  • static pressure
  • dynamic pressure
  • gauge pressure
  • head pressure
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46
Q

gauge pressure

A

pressure in a relative
sense—that is, compared to
atmospheric pressure

Pg = Pabs-Pat

Pg= gauge pressure
Pabs= absolute pressure
Pat= atmospheric pressure

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47
Q

Head pressure

A
  • describe the pressure of the liquid in a tank or pipe.
    p = pgh

p= pressure in Pa
p= density in kg/m^3
g= acceleration due to gravity (9.8m/s^2)
h= depth of liquid in m

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48
Q

types of pressure sensors for (p>1 atm)

A
  • diaphragm
  • bellow
  • bourdon tube
  • solid state pressure sensor
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49
Q

bellow (3)

A
  • Converts a pressure differential into a physical displacement ( a straight-line expansion. )
  • The accordion-shaped sides of the bellows are made from thin metal. When there is a pressure difference, a net force will exist on the flat, front surface of the bellows.
  • The bellows assembly will then collapse like an accordion if p2 is greater than p1 or expand if is p2 less than p1 .
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50
Q

bourdon tube (5)

A
  • A hard metal tube, usually a type of
    bronze or brass, is flattened, and one
    end is closed off
  • The tube is then bent into a curve or arc, sometimes even a spiral.
  • The open end is attached to a header
    by which a pressure can be introduced to the inside of the tube.
  • The tube will deflect when the inside
    applied pressure is different from the
    outside pressure.
  • The tube will tend to straighten out if the inside pressure > the outside pressure, and to curve more if the pressure inside < outside
51
Q

solid state pressure sensor (5)

A
  • pressure ranges of 0 to 100 kPa (0 to 14.7 psi).
  • 3 components - dc power, ground, and the sensor output.
  • The basic sensing element is a small wafer of silicon acting as a diaphragm that, as usual, deflects in response to a pressure difference.
  • This signal conditioning includes temperature compensation and circuitry that provides an output voltage
  • application is in the
    commercial field, in home appliances such
    as dishwashers and washing machines.
52
Q

how to modify SS pressure sensor so it can measure differential pressure?

A

For differential measurement, facilities are provided to allow application of independent pressures p1 and p2 and to the two sides of the diaphragm.

53
Q

characteristics of SS pressure sensor

A

1- sensitivities in the range of 10 to 100mV/kPa
2- response times on the order of 10 ms
3- linear voltage versus pressure within the specified operating range
4- easy of use, only 3 connections: dc power (typically 5V), ground and the sensor output voltage

54
Q

3 types of pressure sensors for (p<1 atm)

A

1- pirani gauge
2- thermocouple
3- ionization gauge

55
Q

pirani gauge (3)

A

-determines the filament temperature through a measure of filament resistance in accordance with the principles
* Filament excitation and resistance measurement are both performed with a bridge circuit.
* The response of resistance versus pressure is highly nonlinear.

56
Q

thermocouple (2)

A
  • A second pressure transducer or gauge measures filament temperature using a
    thermocouple directly attached to the heated filament.
    *Ambient room temperature serves as a reference for the thermocouple, and the
    voltage output, which is proportional to pressure, is highly nonlinear.
57
Q

ionization gauge (3)

A
  • employs electrons, usually from a heated filament, to ionize the gas whose pressure is to be measured, and then measures the current flowing between two electrodes in the ionized environment.
  • The number of ions per unit volume and current depends on gas pressure.
  • This current is then monitored as an approximately linear indication of pressure.
58
Q

how to measure solid flow ?

A

conveyor flow

59
Q

what is conveyor flow (2)

A
  • mass or weight per unit time that is being transported by the conveyor system.
  • To make a measurement of
    flow, it is only necessary to weigh the quantity of material on some fixed length of the conveyor system.
60
Q

how conveyor flow works ? (4)

A
  • A mechanical valve controls the rate from
    the hopper onto the conveyor belt
  • The belt is driven by a motor system
  • The conveyor belt slides over the platform, which deflects slightly due to the weight of material
  • A load cell measures this deflection as an indication of weight
61
Q

flow rate (conveyor belt) formula

A
  • flow rate can be calculated using Q= (WR)/L

Q=flow (kg/min or lb/min)
W = weight of material on section of length, L (kg or lb)
R= conveyor speed (m/min or ft/min)
L= length of weighing platform (m or ft)

62
Q

components to measure liquid flow

A

1- mass or weight flow rate
F=pQ
F= mass or weight flow rate
p = mass density or weight density
Q= volume flow rate
2- flow velocity = distance in liquid travels in the carrier per unit time (m/min or ft/min)
V= Q/A
V= flow velocity
Q= volume liquid flow
A= cross sectional area of flow carrier
3- volume flow rate (gals/min)

63
Q

Restriction flow sensors

A
  • One of the most
    common methods of
    measuring the flow of
    liquids in pipes is by
    introducing a restriction
    in the pipe and measuring the pressure
    drop that results across
    the restriction.
  • When such a restriction
    is placed in the pipe, the
    velocity of the fluid
    through the restriction
    increases, and the
    pressure in the
    restriction decreases.
  • there is a
    relationship between
    the pressure drop and
    the rate of flow such
    that, as the flow
    increases, the pressure
    drops.
64
Q

2 fundamental of electromagnetic radiation

A

1- nature of EM
2- frequency and wavelength

65
Q

nature of EM (3)

A
  • EM radiation is a form of energy that is always in motion—that is, it propagates through space.
  • An object that releases, or emits, such radiation loses energy.
  • One that absorbs radiation gains energy.
66
Q

frequency and wavelength of the fundamental of em radiation

A
  • The frequency represents the oscillation per second as the radiation passes some fixed point in space.
  • The wavelength is the spatial distance between two successive maxima or minima of the wave in the direction of propagation
67
Q

electromagnetic spectrum for UV (ultraviolet radiation)

A

100nm-400nm

68
Q

electromagnetic spectrum for VIS (visible radiation)

A

400nm-800nm

69
Q

electromagnetic spectrum for IR (infrared Radiation)

A

800 nm - 3 (mikro)m

70
Q

8 characteristics of light

A

1- photon
2- energy
3- coherency
4- power
5- spectrum
6- divergence
7- intensity
8- power

71
Q

formula for the characteristics of light

A

Wp= hf= hc/lambda

Wp= photon energy (J)
h= planck constant (Js)
f= frequency (s^-1)
lambda = wavelength (m)

72
Q

formula for intensity of light

A

I= P/A

I= intensity in W/m^2
P=power in W
A= beam cross-sectional area in m^2

73
Q

photometry

A

the science of measurement of light, in terms of its perceived brightness to the human eye.

74
Q

radiometry

A

the science of measurement of radiant energy in terms of absolute power

75
Q

Photodetector Characteristics

A

the spectral sensitivity.

76
Q

most common photoconductive detectors/ photodetectors

A

based on the change in conductivity of a semiconductor material with radiation intensity.

77
Q

photoresistive cells

A

-The change in conductivity appears as
a change in resistance,
- Intensity increase, resistance will decrease exponentially

78
Q

principle of semiconductor photodetector (3)

A
  • a photon is absorbed and thereby excites an electron from the valence to the conduction band.
  • As many electrons are excited into the conduction band, the semiconductor resistance decreases, making the resistance an inverse function of radiation intensity.
  • Lambda max= hc/ Wg
    Lambda max= max detectable radiation wavelength
    h= planck constant
    Wg = semiconductor energy gap (J)
79
Q

How to prevent
the photoconductor
from showing similar thermal effects ?(2)

A

1- operate the devices at a controlled temperature
2- make the gap too large for thermal effects to produce conduction electrons

80
Q

Two common photoconductive semiconductor materials

A
  • Cadmium Sulfide (CdS), with a band gap of 2.42 Ev
  • Cadmium Selenide (CdSe), with a 1.74-eV gap.
81
Q

what is the effect of having large gap energies

A

both materials have a very high resistivity at room temperature.

82
Q

How to overcome high resistivity

A
  • minimize resistance and provide .aximum surface area for the detector
  • R= pl/A
    p= resistivity
  • The area presented to light, A= WL, is large for maximum exposure,
    whereas the electrical length, l = L , is small, which reduces the nominal resistance.
83
Q

characteristics of photoconductive
detectors

A

-Both the PbS and PbSe cells are able to detect infrared radiation, but they are therefore also susceptible to thermal
resistance changes.
-They are usually used in temperature-controlled enclosures
to prevent thermal resistance changes
from masking radiation effects.
-The CdS cell is the most common photoconductive cell in commercial use. Its
spectral response is similar to that of the human eye

84
Q

signal conditioning photoconductive cell

A

-exhibits a resistance
that decreases nonlinearly with radiation intensity.
- the change in resistance is
pronounced where a resistance can change by
several hundred orders of magnitude from
dark to normal daylight.

85
Q

photovoltaic detectors

A
  • generates a voltage that is proportional to
    incident EM radiation intensity
  • convert the EM energy into electrical energy.
    -Applications: EM radiation detectors and power sources converting solar radiation into electrical power
86
Q

principle of photovoltaic cell

A

1- Photons striking the cell pass through the thin p-doped upper layer
2- Photons are absorbed by electrons in the n layer → formation of
conduction electrons and holes
3- The depletion-zone potential of the pn junction separates these
conduction electrons and holes
4- Causes a difference of potential to
develop across the junction
5- The upper terminal is positive, and the
lower negative

86
Q

construction of photovoltaic cell

A
  • The cell is actually a giant diode that is constructed using a
    pn junction between appropriately doped semiconductors
  • first layer: p-doped semiconductor
  • sec layer: pn junction
  • third layer : n-doped semiconductor
  • fourth layer: conductor base
86
Q

IV Curves (a photosensitive diode as a function of
light intensity)

A
  • When the junction is illuminated → a
    voltage is generated across the diode →
    shown by the IV curve crossing the zero
    current axis with a nonzero voltage. This is
    the photovoltaic voltage.
  • the reverse
    current through the diode, when it is
    reverse biased, also increases with
    radiation intensity – Basic photodiode
  • when voltage is zero, but intensity is a non zero, so a short-circuit current will occur
87
Q

short circuit current

A
  • the cell voltage divided by its internal resistance, Vc/Rsc, varies linearly
    with light intensity.
    -short-circuit current
    as the values of current when the IV
    curve crosses the zero-voltage line.
88
Q

relationship between current and Isc

A

the current is proportional to the number of
charge carriers, which is proportional to
the number of photons striking the cell
and thus the radiation intensity

89
Q

signal conditioning of photovoltaic cell

A
  • Since the current to the op amp input must be zero, the feedback
    current through R must equal .
  • Vout= -RIsc
90
Q

characteristics of photovoltaic cell

A
  • used only at low temperatures to prevent thermal effects from obscuring radiation detection.
    -The silicon photovoltaic cell is probably the most common.
91
Q

photodiode detectors

A
  • photons impinging on the pn junction also alter the reverse current-versus-voltage
    characteristic of the diode.
    -the reverse current will
    be increased almost linearly with light
    intensity. Thus, the photodiode is operated in the reverse-bias mode.
92
Q

function of load line

A

to determine the voltage
changes across the diode as a function of light intensity.

93
Q

dark current response

A

the basic diode reverse current, with no illumination of the pn
junction
-

94
Q

advantages of photodiode

A
  • fast time response
  • very small
  • a lens must be used
    to focus light on the pn junction.
95
Q

spectral response of photodiodes

A

typically peaked in the infrared, but with
usable response in the visible band.

96
Q

extension concept of photodiode

A

phototransistor

97
Q

phototransistor

A

the intensity of EM radiation impinging on the collector-base junction of the transistor acts much like a base current in producing an amplified collector-emitter current

98
Q

constructions of photoemissive

A
  • The cathode is maintained at some negative voltage with respect to the wire anode that is grounded through resistor R.
  • The inner surface of the cathode has been coated with a photoemissive agent.
  • This material is a metal for which electrons are easily detached from the metal surface.
99
Q

principles of photoemissive device

A

1- A photon can strike the surface
2- Impart sufficient energy to an electron to eject it from this coating
3- Electron will be driven from cathode to anode by potential and resistor
4- The current that depends on the intensity of light striking the cathode

100
Q

how photomultiplier works

A

1- A photoelectron from the cathode strikes the first dynode to eject several electrons
2- electrons are accelerated to the second dynode
3- eject several more electrons
4- process is repeated until the electrons are greatly multiplied in number
5- photomultiplier (has a gain associated with its
detection

101
Q

construction of photomultiplier tube

A

*many following electrodes, called
dynodes, maintained at successively more positive voltages.
*The final electrode is the anode, which is grounded through a resistor, R

102
Q

specifications of photomultiplier tube

A

1- the number of dynodes and the material
-determine the
amplification or current gain
2- the spectral response ( **The time constant for photomultiplier tubes ranges from 20µs down to 0.1µs.)

103
Q

pyrometry

A
  • a type of remote sensing thermometer
    used to measure the
    temperature of distant objects in the noncontact measurement
104
Q

blackbody radiation

A
  • An idealized object absorbs all radiation
    impinging on it, regardless of wavelength, and therefore becomes an
    ideal absorber.
  • This object also emits radiation without
    regard to any special peculiarities of
    particular wavelength and therefore becomes an ideal emitter
105
Q

explanation on ideal curves of EM radiation as a function of temperature

A
  • as temperature increased, wavelength decreased as blue shifting occurred and the peak shifted to the left as the temperature increased
  • the object will glow as the temperature increase because the wavelength is near the visible band
    -As the temperature is increased, the maximum
    emitted radiation is in the shorter wavelengths, and finally, at very high temperatures, the maximum emitted radiation is near the visible band.
  • Because of this shift in emission peak with
    temperature, an object begins to glow as its
    temperature increases.
106
Q

blackbody approximation

A
  • Most materials emit and absorb radiation at preferred wavelengths,
    giving rise to color, for example. Thus, these objects cannot display
    a radiation energy versus wavelength curve like that of an ideal
    blackbody.
  • Correction factors are applied to relate the radiation curves of real
    objects to that of an ideal blackbody.
  • For calibration purposes, the radiation emitted from a small hole in a metal
    enclosure is close to an ideal blackbody.
107
Q

broadband pyrometer

A

uses the relation between total emitted radiation energy and given temperature

108
Q

types of broadband pyrometer

A
  • total radiation pyrometer
  • IR pyrometer
109
Q

total radiation pyrometer

A
  • Collect radiation from the visible through the infrared wavelengths
  • the detector is often a series of
    microthermocouples attached to a blackened platinum disc
  • Advantage: responds to visible and IR radiation with little regard to
    wavelength
110
Q

IR pyrometer

A
  • Uses a lens formed from silicon or germanium to focus the IR radiation on a suitable detector
  • Handheld, pistol-shaped devices that
    read the temperature of an object toward which they are pointed
111
Q

characteristics of IR pyrometer

A
  • have a readout directly in temperature, either analog or digital
  • switchable range is from 0 to 1000ºC to
    with an accuracy of ±5ºC to ±0.5ºC
112
Q

applications of IR pyrometer

A

1- metal production facilities
2- glass industries
3- semiconductor process
- used to regulate induction heating equipment, crystal pull rates, and other related parameters.

113
Q

narrow band pyrometer

A
  • depends
    on the variation in monochromatic
    radiation energy emission with
    temperature.
  • the intensity of a heated platinum filament is varied
    until it matches an object whose
    temperature is to be determined.
114
Q

another name for narrow band pyrometer and why

A

optical pyrometers because they generally
involve wavelengths only in the visible part of the spectrum.

115
Q

construction of narrow band pyrometer/ optical pyrometer

A

focused on the object
whose temperature is to be determined, and the filter picks out only the desired wavelength, which is usually in the red.

116
Q

how narrow band differentiate between high temperature and low temperature

A
  • At low heating, the filament appears dark
    against the background object,
  • As the filament is heated, it eventually appears as a bright filament against the background
    object
117
Q

types of conventional light sources

A

1- incandescent sources
2- atomic sources

118
Q

characteristics of an incandescent light source

A

1- not monochromatic/ polychromatic bcs the light is distributes in a very broad wavelength spectrum
2- incoherent bcs such light results from molecular vibrations induced by heat , and light from one section of the wire is not associated with the light from another section

119
Q

atomic sources

A

1- If one of these electrons is excited from its normal energy level to a different position (a→b), energy must
be provided to the atom
2- This electron returns to its normal level in a very short time
3- It gives up energy in the form of emitted EM radiation (b’→ a’)

120
Q

Laser sources

A
  • created when electrons
    in the atoms in optical materials like glass, crystal, or gas absorb
    the energy from an electrical current or a light.
  • That extra energy “excites” the electrons enough to move from a
    lower-energy orbit to a higher-energy orbit around the atom’s
    nucleus
121
Q

properties of laser

A

1- monochromatic
- comes predominantly from a particular energy level transition
2- collimated/ coherent
- it emerges from the laser output mirror and remains so for a certain distance from the laser
3- diverged
- the laser light emerges perpendicular to the output mirror, the beam has very little divergence. Typical divergency may be 0.001 rad

122
Q
A

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