Physics. Flashcards
(343 cards)
1
Q
Neutron: Relative Mass? Electrical Charge?
A
Relative Mass: 1 Electrical Charge: 0
2
Q
Proton: Relative Mass? Electrical Charge?
A
Relative Mass: 1 Electrical Charge: +1 (Positive)
3
Q
Electron: Relative Mass? Electrical Charge?
A
Relative Mass: 1/1850 Electrical Charge: -1 (Negative)
4
Q
What is an Element?
A
A pure substance made up of atoms with the same number of protons
5
Q
What is a mixture?
A
A mixture of two or more different elements.
6
Q
What is found in the nucleus?
A
Protons and Neutrons
7
Q
What is a compound?
A
A pure substance made up from more than one element which have been joined together by a chemical reaction.
8
Q
What is the atomic number?
A
Number of protons found in the nucleus.
Also known as the proton number
9
Q
What is the mass number?
A
The number of protons and neutrons found in the nucleus.
10
Q
8 Which is the atomic number and which is the mass number?
O
16
Oxygen
A
8 - Atomic Number
O
16 - Atomic mass
Oxygen
11
Q
What is a molecule?
A
A pure substance which results when two or more atoms of a single element share electrons.
12
Q
What is an Isotope?
A
Atoms of the same element with a different number of neutrons but the same number of protons.
13
Q
What is Ionization?
A
The process of when an atom loses or gains electrons
14
Q
What is a Cation?
A
A positively charged ion.
Typically a metal
15
Q
What is an Anion?
A
A Negatively charged ion.
Typically non-metals
16
Q
Electron Shells: Letter code? Maximum Electrons?
A
1 (K) - Max 2 Electrons
2 (L) - Max 8
3 (M) - Max 18
4 (N) - Max 32
17
Q
What is valency?
A
The amount of electrons needed to fill the outer shell.
18
Q
Atoms with a single outer electron or a single missing electron are…..
A
Highly Reactive
19
Q
Atoms with only a few electrons in the outer shell are good…..
A
Electrical conductors
20
Q
Atoms with 8 or close to 8 electrons in its outer shell are….
A
Poor electrical conductors but good insulators.
21
Q
Atoms with 4 electrons on the outer shell are….
A
Semi-conductors
22
Q
Valance Binding: Valance 1 - 6 and there names?
A
1 - Monovalent 2 - Divalent 3 - Trivalent 4 - Tetravalent 5 - Pentavalent 6 - Hexavalent
23
Q
What is cohesion?
A
The intermolecular force between liquid particle types.
24
Q
What is adhesion?
A
The intermolecular force between dissimilar atoms.
25
Cohesion and adhesion are ..........., Atomic bonding is .........
Cohesion and adhesion are temporary, Atomic bonding is permanent
26
What is covalent bonding?
Sharing electrons to form molecules.
Usually non-metallic elements
27
What is ionic bonding?
One atom transferring electrons to another atom.
28
Ionic bonding: The atom loosing the electron becomes a positive or negative ion?
The atom loosing the electron becomes a positive ion.
29
Ionic bonding: The atom gaining the electron becomes a positive or negative ion?
The atom gaining the electron becomes a negative ion.
30
Can ionic bond conduct electicity when in a solid form?
No, ionic bonds cannot conduct as a solid but when dissolved the solution then becomes conductive.
31
Properties of ionic bonds
```
Strong structures ( Brittle)
High melting points
High Boiling points
```
32
1 slug = ? Kg
14.59kg
33
What is a vector?
A quantity that has both size and direction
34
1 Pound (lb) = ? Newtons
4.4 Newtons
35
Definition of mass...
The quantity of matter.
36
Defenition of weight...
A measure of the gravitational pull of the earth.
37
Equation for Weight...
Weight = mass X gravity
38
Equation for mass...
Mass = weight
———
Gravity
39
Gravity = ? m/s^2
9.8m/s^2
40
Tension
The force of pulling apart.
41
Compression.
A crushing force.
42
Torsion
A twisting force.
43
Shear
Two materials sliding over another.
44
Bending
Combination of compression and tension.
Outside material: Tension
Inside material: Compression
45
Equation for stress:
Stress = Force
———
Area
46
Si Unit for stress...
N/m^2
47
Hooke’s Law
A strain in a solid is proportional to the applied stress within the elastic limit of that solid
48
Spring force equation...
Spring force = Spring constant X Spring stretch or compression
49
Proportional limit
The point at which the deformation is no longer directly proportional to the applied force.
50
Strain equation
Strain = Deformation
——————
Original Length
51
Si Unit for Strain...
Strain has no unit as it is a ratio
52
Young’s modulus equation
Young’s modulus = Stress
———
Strain
53
What is Young’s modulus?
Young's modulus measures the resistance of a material to elastic (recoverable) deformation under load.
A stiff material has a high Young's modulus and changes its shape only slightly under elastic loads (e.g. diamond).
A flexible material has a low Young's modulus and changes its shape considerably
54
What is bulk modulus?
The change in volume of a solid substance as the pressure on it is changed.
55
Bulk modulus equation...
Bulk modulus = Pressure
———————-
Volumetric strain
56
What is Poissons ratio?
The ratio of transvere strain to the axial strain in a stressed member.
57
Si Unit for Force...
Newton
58
Force =
Area X Pressure
59
Pressure =
Force
———
Area
60
Pascals Law:
A pressure change at an point in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.
61
Density Equation:
Density = Weight
————
Volume
62
Si Unit for Density:
Kg/m^3
63
What is creep?
The tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses.
64
Name of converting: Liquid to gas
Evaporation
65
Name of converting: gas to liquid
Condensing
66
Name of converting: solid to liquid.
Melting
67
Name of converting: Liquid to solid.
Freezing
68
Definition for atmospheric pressure.
The entire mass of the air that surrounds earth.
69
Two ways of measuring atmospheric pressure:
Mercury Barometers and Aneroid Barometer
70
5 Basic components of a hydraulic system:
```
Reservoir
Pump or compressor
Lines (pipes)
Directional control valve
Actuating device
```
71
How does a Mercury barometer work?
Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir, then giving a reading.
72
Equation for pressure:
Pressure = pgh
```
p = density
g = Gravity (9.8)
h = Height
```
73
How does a aneroid barometer work?
Uses a accumulation chamber (aneroid cell) made from beryllium and copper, held together with a spring, changes in atmospheric pressure changes cause the cell to expand or contract which gives a reading.
74
What is Archimedean principle?
A body submerged in a liquid displaces a volume of water equal to its own volume.
75
If a body is less dense than the fluid it will......
Float
76
```
SUVAT equation:
t =
u =
v =
a =
s =
Vav =
```
```
t = Time
u= Initial velocity
v = Final velocity
a = Acceleration
s = Distance covered
Vav = Average Velocity
```
77
SUVAT Equation: a =
a = v-u
——
t
78
SUVAT Equation: Vav =
Vav = u+v
——
2
79
SUVAT Equation: v =
V = u+at
80
Symbol for angular velocity:
W
81
Tangential acceleration =
R X A
Radius X Angular Acceleration
82
What is Simple harmonic motion?
Motion which repeats itself precisely
83
Periodic Motion: T =
T = 1/F
84
Periodic Motion: F =
F = 1/T
85
Natural frequency of oscillation (Fn) =
Fn = 1
—- X square root of: K/M
2pi
```
K= The stiffness of the spring
M = The mass of the oscillating body
```
86
Definition of Period:
The time required to complete a full cycle
(T) in seconds
87
Definition of frequency:
The number of cycles per second
| f) in hertz (Hz
88
Definition of amplitude:
The maximum displacement from equilibrium
| A
89
Properties of simple harmonic motion (SHM)
- The velocity and acceleration of the body is always changing
- When velocity = 0, Acceleration = Maximum
- When Acceleration = 0, Velocity = Maximum
90
Definition of free vibration:
Occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. Eg. A play swing
91
Definition of forced vibration:
When an alternating force or motion is applied to a mechanical system. Eg. A washing machine due to imbalance
92
Work done =
Work done = Force X Distance
93
Definition of Actual mechanical advantage (AMA):
The ratio of the output force to the input force.
| This tells us how much easier it is for the worker
94
Definition of Ideal mechanical advantage (IMA):
The mechanical advantage that would exist if there where no friction in the machine.
(The ratio between input distance and output distance)
95
AMA =
Fo/Fi
```
Fo = Force output
Fi = Force input
```
96
IMA =
IMA = Di/Do
```
Di = Distance input
Do = Distance output
```
97
Definition of Efficiency (Eff):
The ratio of the output work to the input work
98
Eff =
Eff = Wo/Wi
or
Eff = Fo X Do
————-
Fi X Di
```
Wo = Work output
Wi = Work input
F = Force
D = Distance
```
99
How is efficiency expressed?
A percentage or a decimal
100
What is the pivot point known as on a lever?
The fulcrum
101
Lever IMA =
IMA = Li/Lo
```
Li = Distance from the input end of the lever to the fulcrum
Lo = Distance from the output end of the lever to the fulcrum
```
102
1st class lever
The fulcrum is between the load and the applied force. Eg. Scissors
103
2nd class lever
The load is between the fulcrum and the applied force. Eg. Wheelbarrow
104
3rd class lever
The applied force is between the load and the fulcrum. Eg. Ice tongs.
The IMA is less than one. There is no force advantage, however there is a speed advantage, the work can be done in less time.
105
Pulleys IMA =
The number of strands supporting the load
106
Pulleys: The length of the pulley cord (Di) =
2 X the distance raised (Do)
107
Wheel and axle IMA =
IMA = R/r
```
R = Radius of the wheel
r = Radius of the axle
```
108
Inclined plane IMA =
IMA = 1/ Sin(-0)
109
Screw jack: What is the pitch (p) of the screw?
The distance between threads
110
Screw jack IMA =
IMA = 2 pi r
——-
P
```
r = Radius
P = Pitch
```
111
Hydraulic press IMA =
IMA = R^2 / r^2
```
R = Larger piston radius
r = Smaller piston radius
```
112
Newton’s first law:
Law of inertia
A body at rest remains at rest and a body in motion continues to move at constant velocity unless acted upon by an unbalanced force
113
Newton’s second law:
To have a change in speed or direction an unbalanced force must act on the object.
F=MA
114
Newton’s third law:
Every action has an equal and opposite reaction.
115
What is centripetal force?
A force that action a body moving in a circular path and is directed towards the centre around which the body is moving.
116
Centripetal acceleration equation:
Velocity^2
————-
Radius
117
What is static friction?
The force between two objects that are not moving relative to each other.
118
What is limiting friction?
The maximum value of static friction when motion is impending.
119
What is rolling friction?
The frictional force associated with the rotational movement of a wheel or circular object along a surface. EG. A car wheel
120
What is kinetic friction (Dynamic friction)?
Occurs when two objects are moving relative to each other and rub together.
Usually does negative work, slowing something down.
121
Two types of kinetic friction...
Sliding friction
| Fluid friction - Friction between a solid object as it moves through a liquid or gas
122
Kinetic energy (KE) equation:
1/2 MV^2
123
Definition of kinetic energy:
Energy which a body possesses by virtue of being in motion
124
Potential energy (PE) equation:
mgh
Mass x gravity x height
125
Definition of potential energy:
The energy possessed by a body by virtue of its position relative to others, stresses within itself, electric charge and other factors.
126
Defenition of power:
The rate of doing work
127
Equation for power:
Work/time
128
Definition of momentum:
The quantity of motion of a moving body.
129
Equation for momentum:
Mass X Velocity
130
Equation for inelastic collisions:
m1v1 + m2v2 = (m1+m2) V
131
Definition of inelastic collision:
A collision in which kinetic energy is not conserved due to the action of internal friction.
132
Definition of elastic collision:
Collisions that occur between bodies that deform very little in the collision. Therefore we assume no energy is lost and both kinetic and momentum are conserved.
133
Equation for elastic collision:
V1 - V2 = V2-V1
134
Torque definition:
Torque is the force applied to a body that is pivoted at a point that tends to cause a rotation around the pivoted point.
135
Equation for torque:
Torque = Radius X Force X sin$
136
Extension of a torque wrench: Scale reading =
Specified torque X L/ L+X
```
L = Distance between the driving tang and the centre fo the handle
X = Length of extension spanner between centres
```
137
Forces: What is a couple?
A pair of forces of magnitude that are equal and opposite but applied at points separated by a distance perpendicular to the forces. The combined moment of the forces produces a torque on the object they act on. EG. Taping. Hole
138
Equation for torque applied by a couple:
One of the forces (F) X distance to centre of rotation (r) X 2
Or
One fo the forces (F) X distance between the force (d) = FD
139
Where is an earth gyro used?
Artificial horizons and altitude indicators
140
What is differential pressure?
The maximum difference between cabin pressure and atmospheric pressure which the pressurisation system can sustain.
141
What does the term “saturated” mean?
When the air contains the maximum amount of vapour possible for a particular temperature.
Warm air can hold more vapour then cold air
142
What is absolute humidity? What is its unit?
The amount of water vapour that is present in a unit plume of air.
Expressed in grams per cubic meter
143
What is relative humidity?
The amount of water vapour actually in the air divided by the amount of water vapour the air can hold.
144
If unsaturated air is cooled, relative humidity ......
Increases
145
What is dew point?
The temperature air would have to be cooled to in order for saturation to occur
146
What is actual vapour pressure? What is it measured in?
The partial pressure exerted by the water vapour present in a parcel.
Measured in Millibars
147
What is condensation?
The phase change of a gas to liquid.
148
What us dry bulb temperature?
The actual air temperature
149
What is mixing ratio?
The mass of water vapour in a parcel divided by the mass of the dry air in the parcel. (Not including water vapour)
150
What is saturation to air?
The condition under which the amount of water vapour in the air is the maximum possible at the existing temperature and pressure.
151
What is the saturation vapour pressure?
The maximum partial pressure that water vapour molecules would exert if the air were saturated with vapour at a given temperature.
152
What is specific humidity?
The mass of water vapour in a parcel divided by the total mass of the air in the parcel. (Including water vapour)
153
What is sublimation?
The transition from sold to gas.
154
What is the wet bulb temperature?
The lowest temperature that can be obtained by evaporating water into the air at constant pressure.
155
What is specific gravity?
The ratio of the density of a substance to the density of a given reference material.
(No unit as it is a ratio)
156
Specific gravity equation:
Density of the substance/ Density of water
157
What is the density of water?
997 kg/m^3
158
What is ideal fluid/inviscid fluid?
A fluid which has no resistance to shear stress
159
What is dynamic viscosity?
Determines the dynamics of an incompressible fluid
160
What is kinematic viscosity?
The dynamic viscosity divided by the density
161
What is volume viscosity/ bulk viscosity?
Determines the dynamic of a compressible fluid
162
What is a non-Newtonian?
Fluids without a constant viscosity, there viscosity cannot be described by a single number
163
Most common type of Viscometer?
Glass capillary viscometer
164
Name the 4 types of viscometer?
Glass capillary
Zahn cup
Stormer (measured in kerbs, unique to the stormer)
Vibrating viscositors
165
Kinematic viscosity equation:
Dynamic viscosity/ density
166
Viscosity of water at 25 degrees:
8.90 x 10^-4 pa
167
Profile drag includes:
Form drag
Interference drag
Skin friction
168
Wave drag occurs when.....
A solid object is moving through a fluid at or near the speed of sound in that fluid
169
Drag equation:
Coefficient x (density x velocity^2) x reference area
—————————-
2
170
Drag coefficient equation:
```
Drag
—————-
Density x area x v^2
——
2
```
171
Viscosity equation:
-BV
B = Constant that depends on the properties of the fluid and the dimensions of the object
V = The velocity of the object
172
Definition fo drag coefficient:
A dimensionless quantity that describes a characteristic amount of aerodynamic drag caused by fluid flow.
173
What is the Bernoulli principle?
An increase in speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluids potential state.
174
Venturi principle:
The reduction in fluid pressure that results when a fluid flows through a constricted section of a pipe, but velocity increases.
175
What is a Newtonian fluid?
Where stress is directly proportional to rate of strain or fluid with a constant viscosity at a fixed temperature or pressure
176
Angle of attack:
The angle between the chord line of the wig and the relative wind direction
177
Boundary layer:
A thin layer of air in direct contact with the wing surface, which due to friction is actually stationary (relative to the wing)
178
Freezing point of water:
0 degrees Celsius
| 32 degrees Fahrenheit
179
Absolute zero:
If we cool any substance enough we can cause all molecular motion to cease.
180
Conventions: centigrade to kelvin
K = C + 273
181
Conversion: Fahrenheit it rankin
R = F + 460
182
Boyles law:
The pressure of a given ,ass of an ideal gas is inversely proportional to its volume at a constant temperature.
183
Boyles law equation:
P1V1=P2V2
184
Charles Law:
The volume of an ideal gas at constant is directly proportional to the absolute temperature
185
Charles law equation:
V1/T1 = V2/T2
186
Gay-lussacs law:
The pressure of a given mass of gas varies directly with the absolute temperature of the gas, when the volume is kept constant.
187
Gay-lussacs law equation:
P1/T1 = P2/T2
188
Compressor discharge pressure (CDP):
The pressure of the air when it leaves the compressor
189
Compression ration equation:
Compression ratio = CDP/CIP
CDP - Compressor discharge pressure
CIP - Compressor inlet pressure
190
Coefficient of linear expansion:
Used to account for different rates of materials (Unit = degrees Celsius)
191
Coefficient of linear expansion equation:
^L=a Lo ^T
```
^L = Change in temperature
a = coefficient of linear expansion
Lo = original length of the rod
^T = Change in temperature
```
192
The temperature of a body is .....
A measure of the average kinetic energy of the molecules of that body.
193
Two dimensional area thermal expansion equation:
^A = 2a Ao ^T
^A = change in area of the body
^T the change in temperature
Ao = Original area of the body
a = The coefficient of linear expansion
194
Three dimensional volume thermal expansion equation:
^V = 3 a Vo ^T
```
Vo = Original volume of the body
a = Coefficient of linear expansion
^V = Change in volume of the body
^T = Change in temperature
```
195
What happens to water between 0 and 4 degrees Celsius?
It expands when cooled
196
1 Calorie = ? J
4186J
197
1 BTU = ? Calories
0.252 Calories
198
Heat gained or lost equation:
Q = m C ^T
```
Q= heat gained or lost (J)
M = mass of the body (KG)
C = The specific heat of the substance (J/kg Degrees Celsius)
^T = The temperature change (Degrees Celsius or Kelvin)
```
199
Latent heat:
The energy required to change the phase of a substance.
200
Latent heat energy required equation:
Q=ML
```
Q= Latent heat energy required
M = Mass
L = Specific latent heat of fusion or evaporation
```
201
Each time water changes state .....
Energy is absorbed or released
202
Convection:
The transfer of heat by the actual movement of the warmed matter.
203
Conduction:
The transfer of energy through matter from particle to particle.
204
Radiation:
Electromagnetic waves that directly transport energy through space.
205
Refrigeration:
The removal and relocation of heat.
206
4 components of a refrigeration system:
Compressor
Condenser
Metering device
Evaporator
207
Heat pump:
A device that moves heat from one location to another using work.
208
What type of process is Boyles law?
Isothermal (Temperature)
209
What type of process is Charles law?
Isobaric (Pressure)
210
What type of process is Gay-Lussac’s Law?
Isochoric (Volume)
211
Adiabatic:
When a change in the volume and pressure of the contents of a system takes place without exchange of heat between the system and its surroundings.
212
Which gas laws are Adiabatic?
Boyles law - ?
Charles law - Not Adiabatic
Gay Lussacs law - Not Adiabatic
213
Thermodynamics: Work done by a piston equation:
Work = Pressure X Change in volume
214
Internal Energy (u)
Energy contained in a system
Measured in Joules
215
Enthalpy
The sum of the internal energy added to the product fo the pressure and volume of a system.
(H)
216
Enthalpy Equation:
H = E + PV
```
H = Enthalpy
E = Internal Energy
P = Pressure
v = Volume
```
217
1st law of thermodynamics:
The internal energy (E) of a system tends to increase, if energy is added as heat (Q) and trends to decrease if energy is lost as work (w) is done by the system.
218
Heat energy added to the system (Q) =
Work done by the system (w) + Change in internal energy (u)
219
2nd law of thermodynamics
The total entropy of an isolated system can never decrease over time and is constant if and only if all processes are reversible.
220
Thermal efficiency equation:
Thermal efficiency = 1 - temperature of cold source/temperature of hot sauce
221
Isentropic process:
An idealised thermodynamic process that is both adiabatic and reversible.
222
3rd law of thermodynamics:
The entropy of a system at absolute zero is a well defined constant.
223
Entropy:
A quantity representing the unavailability of a systems thermal energy for conversion into mechanical work.
224
Speed of light:
3.00 x 10^8 m/sec
225
What range are visible lights?
4,000A (Ultraviolet) - 7,000A (Infrared)
226
Speed of electromagnetic radiation (c) equation:
C= Frequency (f) X wavelength
227
What two types of waves for EM radiation consist of?
An electrical field (E field) and a magnetic field (B field), moving at 90 degrees to each other.
228
Index of radiation (n) equation:
n = Speed of light in free space (C)/speed of light in the substance (v)
229
Index of refraction:
The ratio of the speed of light in a vacuum to the speed of light in the substance.
230
Can electromagnetic waves travel through opaque materials containing free electrons and why?
No as the waves lose so much energy to the electrons.
231
Refraction:
The change in direction of a wave passing from one medium to another (Occurs when at an angle other than 90 degrees)
232
Chromic Aberration:
A failure of a lens to. Focus all colours to the same point. It is cause be dispersion.
233
Dispersion:
The phenomenon in which the phase velocity of a wave depends on its frequency.
234
Converging/ positive lens:
Alters a plane wavefront to make the light waves pass through a point or focus.
235
Smells law:
A formula used to describe the relationship between the angles of incidence and reflection.
236
Snells law equation:
N1 X sin$ 1 = N2 X sin$2
```
N1 = Incident index
$1 = Incident angle
N2 = Refracted index
$2 = Refracted angle
```
237
Focus/principle focus:
The point on the axis of a lens which parallel rays of light converge or from which they appear to diverge after refraction or reflection.
238
Focal length:
Distance from principle focus to the centre of the lens
239
Aberration:
A departure of an image forming optical system from ideal behaviour.
240
Finding the image by formula, Lens formula:
1/U +1/V = 1/F
```
U= Distance of the object from the lens centre
V = Distance of the image from the lens centre
F = Focal length of the lens
```
241
Which is positive and which is negative?
| Diverging lens & Converging lens
```
Diverging lens (-f)
converging lens (+f)
```
242
Lens power =
1/F
F=Focal length of the lens
243
Unit of lens power:
Dioptre (D)
244
Front silvered mirrors:
- Metallic layer on the front surface.
- Very fine metal particles are deposited on glass either from solution or from metal vapour in a vacuum
- large mirrors used in reflecting telescopes are made this way
- Metal surfaces are easily damaged
245
Reflecting Prisms:
A glass (or clear plastic) reflecting prism provides a cheap and practical plane mirror by using the effect of total internal reflection.
246
How does internal reflection occur?
Internal reflection occurs when the angle of incidence of a ray exceeds the critical angle (c) for the medium.
247
Principle axis:
A line passing through the centre of the sphere and attaching to the mirror in the exact centre of the mirror.
248
Centre of curvature (c):
The point in the centre of the sphere from which the mirror was sliced.
249
Vertex (A):
The point on the mirrors surface where the principle axis meets the mirror. (Geometric centre of the mirror)
250
Focal point (F):
Midway between the vertex and the centre of curvature.
251
Radius of curvature (R):
The distance from the vertex to the centre of curvature.
252
Focal length:
Distance from the mirror to the focal point.
253
Why are convex mirrors used, and where are they used?
Used to fit more detail into the mirror by shrinking it. EG. Car mirror
254
Fibre optics:
Uses light to send information (data)
255
Three basic functions of fibre optics:
Transmitter: Convert an electrical input signal to an optical signal.
Optical fibre: Transport the optical signal.
Receiver: To convert the optical signal back to an electrical signal.
256
Transmitter consists of what two components?
An interface circuit and a source drive circuit.
257
Fibre optics: What does a transmitter drive circuit do?
Converts the electrical signals to an optical signal, it does this by varying the current flow through the light source.
258
Fibre optics: Two types of optical sources:
Light emitting diodes (LED’s) and laser diodes
259
Fibre optics: What does the optical source do?
The optical source launches the optical signal into the fibre.
260
Fibre optics: What does the receiver consist of?
The optical sector and the signal conditioning circuits.
261
Fibre optics: What does the signal conditioning circuit do?
The signal conditioning circuit condition the detector output so that the receiver output matches the original input to the transmitter.
262
Fibre optics: An optical sector can either be:
A semi conductor positive intrinsic negative (PIN) or an avalanche photodiode (APD)
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Name some advantages of fibre optics:
- System performance
- No crosstalk
- Immunity to noise (EMI & RFI)
- Difficult to tap
- Lower bit error rates
- Signal security
- Reduced size and weight
- Resistant to radiation and corrosion
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Negatives of fibre optics:
- Expensive
- Lack of standardisation
- Company’s are used to electrical and do not want to switch
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Bandwidth:
The amount of information that can be transmitted at one time.
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How does frequency effect bandwidth?
The higher the frequency the greater the bandwidth.
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What type of light is generally used for fibre optics?
Infrared
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3 Parts structure of fibre optics:
The core
Cladding
Coating of buffer
269
What is the core of a fibre optics cable made from?
A Dialectic material. (conducts no electricity)
Generally Glass
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What is the purpose of the cladding in fibre optics? (4x answers)
- Reduce loss of light from the core into the surrounding air
- Reduces scattering loss at the surface of the core
- Adds mechanical strength
- Protects fibre from absorbing contaminants.
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What is the purpose of the coating or buffer on fibre optics?
To protect fro physical damage.
Also prevents scattering losses caused by microbends
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How is light described by ray law?
Light is described as a simple ray.
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Ray theory: Two types of rays that can propagate along an optical fibre:
Meridional rays and Skew rays
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Meridional rays:
Rays that pass through the axis of the optical fibre.
Used to illustrate the basic transmission properties of optical fibre
Classified into bound or unbound
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Skew rays:
Rays that travel through an optical fibre without passing through its axis.
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Bound rays:
Remain in the core and propagate along the axis of the fibre.
They propagate through the fibre by total internal reflection.
277
Unbound rays:
Rays are refracted out of the fibre core.
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Acceptance Angle:
The maximum angle to the axis of fibre that light entering the fibre is propagated
(The value of the acceptance angle is dependent on the fibre properties and transmission conditions.
279
Numerical Aperture:
A measurement of the ability of an optical fibre to capture light.
(The NA is also used to define the cone of acceptance of an optical fibre.)
280
Numerical Aperture (NA) equation:
NA = no X Sin$a = (n1^2 - n2^2) X 1/2
281
Mode theory:
Used to describe the propagation of light along an optical fibre.
(Used to describe the properties that ray the ray theory is unable to explain.)
282
How does the mode theory describe the propagation of light along a fibre?
The mode theory uses electromagnetic wave behaviour to describe the propagation of light along a fibre.
283
How is a plane wave described?
A plane wave is described by its direction, amplitude and wave length of propagation.
A plane wave is a wave whose surfaces of constant phase are infinite parallel planes normal to the direction of propagation.
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Wavelength of a plane wave equation:
Wavelength = C/fn
```
C = Speed of light in a vacuum
f = Frequency of the light
n = Index of refraction of the plane wave medium
```
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Plane waves repeat at a distance equal to:
wavelength/sin$
286
Cut-off wavelength:
The wavelength at which a mode ceases to be bound.
Which can be caused by a change in wavelength.
287
Fundamental mode:
An optical fibre is always able to propagate at least one mode. This is known as the fundamental mode.
288
Single mode fibre:
An optical fibre that operates above the cut-off wavelength.
| At a longer wavelength
289
Dispersion:
The change in the propagation constant for different wavelengths.
290
Chromic Dispersion:
The change in the propagation constant for different wavelengths.
291
Modal dispersion:
The change in propagation constant for different modes.
292
Modes:
A set of guided electromagnetic waves.
293
How is the order of each mode indicated?
The order of each mode is indicated by the number of field maxima within the core of the fibre.
294
Transverse Mode:
A mode of electromagnetic radiation with a particular electromagnetic field pattern of radiation in the plane perpendicular to the radiations propagation direction.
295
Cladding modes:
Modes that become trapped in the cladding region.
296
Mode coupling:
The exchange of power between modes.
297
Normalised Frequency:
Electromagnetic waves bound to an optical fibre are described by the fibres normalised frequency.
298
What does the normalised frequency determine?
How many modes a fibre can support.
It is a dimensionless quantity.
299
As the normalised frequency increases, the number of modes supported by the fibre .......
Increases
300
Two types of optical fibre:
Single mode fibres
| Multi mode fibres
301
Single mode fibres:
Core size is small, diameter is around 8 - 10 micrometers
Allows only the fundamental or lowest order mode (around 1300 manometer wavelength)
302
Which mode fibres have a lower signal loss and a higher bandwidth, Single mode or multi mode?
Single mode
303
Multi mode fibres: As the number of modes increase the effect of modal dispersion .......
Increases
304
Modal Dispersion:
And what does it effect?
Modes arrive at the fibre end at slightly different times. This time difference causes the light to spread. This effects the systems bandwidth.
305
Attenuation:
Reduces the amount of optical power transmitted by the power.
Mainly as a result of light absorption, scattering and bending losses.
306
Signal Attenuation:
The ratio of optical input power (Pi) to the optical output power (Po).
307
Attenuation Equation:
(10/L) Log^10 (Pi/Po)
```
L = Length (KM)
Pi = Input power
Po = Output power
```
308
Unit of attenuation:
Decibel/kilometre (dB/km)
309
Absorption:
The portion of attenuation resulting from the conversion of optical power into another energy, EG. Heat.
310
Absorption in optical fibres is explained by three factors:
- Imperfections in the atomic structure of the fibre material
- The intrinsic or basic material-material properties
- The extrinsic material-material properties
311
Intrinsic Absorption:
Caused by basic material-material properties. Intrinsic absorption sets the minimal level of absorption.
312
Extrinsic Absorption:
Caused by impurities introduced into the fibre material. This causes an electronic transition of these metal ions from one energy level to another.
313
Scattering:
Caused by the interaction of light with density fluctuations within a fibre.
Density changes are produced when the fibres are manufactured.
314
Rayleigh Scattering:
Occurs when the size of the density function (Fibre defect) is less than 1/10th of the operating wavelength of light.
315
As the wavelength increases, the loss caused by Rayleigh scattering .......
Decreases
316
MIE Scattering:
Caused by these large defects in the fibre core, scatters light out of the fibre core.
Occurs if the size of the defect is greater than 1/10th of the operating wavelength of light.
317
Bending Loss:
Bending the fibre also causes attenuation. Bending loss is classified according to the bed radius of curvature microbes loss or macrobend loss.
318
Microbends:
Small microscopic bends of the fibre axis that occur mainly when a fibre is cabled. Caused by small imperfections in the fibre.
319
Macrobends:
Bends having a large radius of curvature relative to the fibre diameter.
During installation if fibres are bent too sharply, macrobend losses will occur.
320
Two types of dispersion in optical fibres:
Intramodal dispersion
| Intermodal dispersion
321
Intramodal dispersion:
AKA Chromiatic Dispersion
- Depends on the fibre materials.
- Categorised into material dispersion and wave guide dispersion
- Occurs in all types of fibre
- Occurs because different colours of light travel through different materials and different waveguide structures at different speeds
322
Intermodal dispersion:
AKA Modal dispersion
- Causes the input light pulse to spread.
- The pulse spreads because each mode propagates along the fibre at different speeds and as a result travels a different distance in the same span.
323
Which type of fibres exhibit the lowest amount of total dispersion but the highest amount of bandwidth?
Single mode fibres
324
Analogue Transmission:
The incoming information signal is used to control the power output from the LED or the laser.
At the far end the receiver converts light to an electrical signal.
325
Digital transmission:
The information signal is represented by a sequence of on/off levels. The “on” state is referred to as logic 1 and the “off” state as logo 0.
This approach means it ignores noise and distortion.
326
Refractive Index Profile:
Describes the value of refractive index as a function of radial distance at any fibre diameter.
327
Step - Index fibre:
The refractive index of the core is uniform and undergoes an abrupt change at the core-cladding boundary.
328
Graded-Index Fibres:
Th refractive index of the core varies gradually as a function of radial distance from the fibre centre.
329
Standard Core sizes:
Multimode step index
Multimode graded index
Single mode fibres
Multimode step index: 50 - 100 Micrometers
Multimode graded index: 50, 62.5, 85 & 100 Micrometers
Single mode fibres: 8 - 10 Micrometers
330
Multimode step Index:
- Large core diameters and NA
| - Limited bandwidth capabilities
331
Multimode graded index fibre:
- Relatively high source to fibre coupling efficiency
- Low loss
- Low sensitivity to bending
- High bandwidth
- Expansion capability
332
Two types of single mode step-index:
Matched cladding
| Depressed Cladding
333
Matched Cladding:
Means that the fibre cladding consists of a single homogeneous layer of dielectric material
334
Depressed Cladding:
Means that the fibre cladding consists of two regions: The inner and outer cladding regions
335
Single mode step-index fibre:
- Low Attenuation
| - High bandwidth properties
336
Optical time domain reflectometer (OTDR):
- Main field measurement technique, used for conducting field measurements on installed optical fibres of 20 meters or more in length.
- Requires access to only one end
- Measures attenuation
- Identifies losses, breaks and faults.
337
Optical Loss test set (OLTS):
Combines the power meter and source functions into one unit.
338
Point Defect:
Temporary or permanent local deviation of the OTDR signal upward or downward direction.
- Caused by connectors, splices or breaks along the fibre length.
339
Optical power meter:
Measures fibre attenuation and transmission loss in the field. Used when the cable is less than 50 meters.
- Must be connectors both ends
- Uses a light source
340
Intensity of sound (Decibels) Equation:
Decides = 10 log(intensities of the sound/ 10^-12)
341
Heat required to change a liquid to a gas is called the heat of .......
Vaporisation.
342
Centripetal force=
MV^2/r
343
Constant velocity =
| using gravity and height
V=square root of (2gh)
