Definitions Flashcards
Add CH 19 and 20 notes and all of nuclear and medical physics when done
1
Q
Absolute uncertainties
A
The interval that a value is said to lie within, with a given level of confidence.
2
Q
Accuracy
A
A measure of how close a measurement is to the true value
3
Q
Analogue Apparatus
A
Measuring apparatus such as rulers, beakers and thermometers that rely on the experimenter reading off a scale to determine the measurement.
4
Q
Anomalies
A
Data points that don’t fit the pattern of the data. You should determine
why an anomalous result has occurred before removing it. Repeat readings help remove anomalies.
5
Q
Control Variables
A
Variables that must remain the same throughout an
experiment so as to not affect the results.
6
Q
Dependent Variables
A
The variable being measured in an experiment. It is
dependent on the independent variable. The dependent variable should be plotted
on the y-axis of a graph.
7
Q
Digital Apparatus
A
Measuring apparatus such as ammeters, voltmeters and
digital calipers that digitally measure and display a measurement.
8
Q
Fiducial Marker
A
A thin marker, such as a splint, that is used to ensure readings
are taken from the same place each time. They are used to improve the accuracy
of measurements.
9
Q
Gradient
A
The change in the y-axis value over the change in the x-axis value between two points. Ifthe graph is curved, a tangent can be drawn to calculate the gradient at a specific point.
10
Q
Independent Variables
A
The variable that is changed by the experimenter in an
experiment. The independent variable should be plotted on the x-axis of a graph.
11
Q
Line of Best Fit
A
A line drawn on a graph to demonstrate the pattern in the plotted
data points.
12
Q
Percentage Uncertainties
A
The uncertainty of a measurement, expressed as a
percentage of the recorded value.
13
Q
Precision
A
A measure of how close a measurement is to the mean value. It only
gives an indication of the magnitude of random errors, not how close data is to the
true value.
14
Q
Prefixes
A
Added to the front of units to represent a power of ten change
15
Q
Random Errors
A
Unpredictable variation between measurements that leads to a spread of values about the true value.
Random error can be reduced by taking repeat measurements.
16
Q
Repeatable
A
The same experimenter can repeat a measurement using the same method and equipment and obtain the same value.
17
Q
Reproducible
A
An experiment can be repeated by a different
experimenter using a different method and different apparatus, and
still obtain the same
results.
18
Q
Resolution
A
The smallest change in a quantity that causes a visible change in the reading that a measuring instrument records.
19
Q
Resolution of Forces
A
The splitting of a force into its horizontal and vertical
components.
20
Q
Scalar Quantities
A
A quantity that only has a magnitude, without an associated
direction. Examples include speed, distance and temperature.
21
Q
SI Base Units
A
The standard units used in equations. They are: metres, kilograms, seconds, amps, Kelvin and moles.
22
Q
Significant Figures
A
A measure of a measurement’s resolution. All numbers
except zero are counted as a significant figure. When zeros are found immediately
after a decimal place, they too are counted.
23
Q
Systematic Errors
A
Causes all readings to differ from the true value by a fixed amount. Systematic error cannot be corrected by repeat readings, instead a different technique or apparatus should be used.
24
Q
Triangle of Forces
A
A method of finding the resultant force of two forces. The two forces are joined tip to tail and the result is then the vector that completes the triangle.
25
Vector Quantities
A quantity that has both a magnitude and an associated
direction. Examples include velocity, displacement and acceleration
26
Vernier Scales
: The type of scale used on calipers and micrometers, that involve
reading from a fixed scale and a moving scale to produce accurate
measurements.
27
Zero Errors
A form of systematic error, caused when a measuring instrument doesn’t read zero at a value of zero. This results in all measurements being offset by a fixed amount.
28
Acceleration
The rate of change of velocity
29
Average Speed
Distance over time for the entire region of interest
30
Braking Distance
The distance travelled between the brakes being applied and the vehicle coming to a stop. It is affected by the vehicle and road conditions
31
Displacement
The direct distance between an objects starting an ending positions. It is a vector quantity and so has a direction and magnitude
32
Displacement-Time Graphs
Plots showing how displacement changes over a period of time. The gradient gives the velocity. Curved lines represent an acceleration
33
Free-Fall
An object is said to be in free fall when the only force acting on it is the force of gravity
34
Instantaneous Speed
The exact speed of an object at a specific given point
35
Projectile motion
The motion of an object that is fired from a point and then upon which only gravity acts. When solving projectile motion problems, it is useful to split the motion into horizontal and vertical components (or use matrices)
36
Reaction Time
The time taken to process a stimulus and trigger a response to it. It is affected by drugs alcohol and tiredness
37
Stopping Distance
The sum of thinking distance and braking distance for a driven vehicle
38
Thinking distance
The distance travelled in the time it takes for the driver to react. It is affected by alcohol, drugs and tiredness.
39
Velocity-Time graphs
Plots showing how velocity changes over a period of time, The gradient gives acceleration. Curved lines represent changing acceleration
40
Velocity
The rate of change of displacement, It is a vector quantity and so has a direction and magnitude
41
Archimedes' Principle
The upwards force acting on an object submerged in a fluid, is equal to the weight of the fluid it displaces
42
Centre of Gravity
The single point through which the object's weight can be said to act
43
Centre of mass
The single point through which all the mass of an object can be said to act
44
Couple
Two equal and opposite parallel forces that act on an object through different lines of action. It has the effect of causing rotation without translation
45
Density
The mass per unit volume of a meterial
46
Drag
The frictional force that an object experiences moving through a fluid
47
Equilibrium
For an object to be in equilibrium, both the resultant force and resultant moment acting on the object must equal to zero
48
Free-Body Diagram
A diagra showiing all the forces acting on an object.
49
Friction
The resistive force produced when there is relative movement between two surfaces
50
Moment of Force
The product of a force and the perpendicular distance form the line of action of the force and the pivot.
51
Newton
The unit of force
52
Newton's Second Law
The sum of the forces actinf on an object is equal to the rate of momentum of the object
53
Normal Contact Force
The reaction force between an object and surfact
54
Pressure
he force that a surface experiences per unit area. It is measured in Pascals (Pa)
55
Principle of Moments
For an object to be in equilibrium, the sum of the clockwise moments acting about a point must be equal to the sum of the anticlockwise moments acting around the point
56
Tension
The result of two forces acting on an objet on opposite outwards directions
57
Terminal Velocity
The maximum velocity of an object that occurs when the resistive and driving forces acting on the object are equal to each other
58
Upthrust
The upwards force that a fluid applies on an object
59
Weight
The product of an object's mass and the gravitational field strength at its location
60
Conservation of Energy
In a closed system with no external forces the total energy of the system before an event is equal to the total energy of the system after the event, The energy however does not need to be in the same form after the event as it was before the event
61
Efficiency
The useful output of a system divided by the total output
62
Gravitational Potential Energy
The energy gained by an object when it is raised by a height in a gravitational field
63
Kinetic Energy
The energy an object has due to its motion. It is the amount of energy that would be transferred when it decelerates to rest
64
Power
The work done or energy transferred by a system divided by the time taken fo rthat to be done
65
Work Done
The energy transferred when a force moves an object over a distance
66
Brittle
A brittle object is one that shows very little strain before reaching its breaking stress
67
Compression
The result of two coplanar forces acting into an object. Compression usually results in a reduction in the length of the Object
68
Compressive Deformation
The changing of an objects shape due to compressive forces
69
Ductile
A material is ductile if it can undergo very large extensions without failure. Ductile materials can be stretched int wires.
70
Elastic Deformation
If a material deforms with elastic behaviour, it will return to its orginal shape when the deforming forces are removed. The object will not be permanently deformed
71
Elastic potential energy
The energy stored in an object when it is stretched. It is equal to the work done to stretch the object and can be determined form the area under a force-extension graph
72
Extension
The increase in an objects length away from its original length
73
Force-Extension graph
A plot showing how an object extends as the force applied increases. For an elastic object, the gradient should be linear up to the limit of proportionality. The gradient gives the spring constant
74
Hooke's Law
The extension of an elastic object will be directly proportional to the force applied to it up to the objects limit of proportionality
75
Plastic Deformation
If a material deforms with plastic behaviour, it will not return to its original shame when the deforming forces are removed. The object will be permanently deformed
76
Polymeric
A material made from polymers
77
Spring constant
The constant of proportionality for the extension of a spring under a force. The higher the spring constant, the greater the force needed to achieve a given extension
78
Strain
The ratio of an objects extension to its original lengths. It is a ratio of two lengths and so has no unit
79
Stress
The amount of force acting per unit area. Its unit is Pascal
80
Tensile deformation
The changing of an objects shape due to tensile forces
81
Ultimate Tensile Strength
The maximum stress than an object can withstand before fracture occurs
82
Young Modulus
The ratio of stress to strain for a given material. Its unit is the Pascal
83
Conservation of momentum
The total momentum of a system before an event must be equal to the total momentum of the system after the event, assuming no external forces act.
84
Elastic Collisions
A collision in which the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision
85
Impulse
The change in momentum of an object when a force acts on it. It is equal to the product of the force acting on the object and the length of time over which it acts
86
Inelastic collisions
A collision in which the total kinetic energy of the system before the collision is not equal to the kinetic energy of the system after the collision
87
Linear Momentum
The product of an objects mass and linear velocity
88
Newton's First Law
An object will remain in its current state of motion unless acted on by a resultant force. An object requires a resultant force to be able to accelerate
89
Newton's Third Law
Ever action has an equal and opposite reaction. If an object exerts a force on another object, Then the other object must exert a force back, that is opposite in direction and equal in magnitude
90
Conductors
A material that allows the flow of electrical charge. Good conductors
have a larger amount of free charge carriers to carry a current.
91
Conservation of Charge
The total charge in a system cannot change
92
Conventional Current
The flow from positive to negative, used to describe the
direction of current in a circuit.
93
Coulomb
The unit of charge
94
Electric Current
The rate of flow of charge in a circuit
95
Electrolytes
Substances that contain ions that when dissolved in a solution, act
as charge carriers and allow current to flow.
96
Electron Flow
The opposite direction to conventional current flow. Electrons flow
from negative to positive
97
Elementary Charge
The smallest possible charge, equal to the charge of an electron.
98
Insulators
A material that has no free charge carriers and so doesn’t allow the flow of electrical charge
99
Kirchhoff's First Law
A consequence of the conservation of charge. The total current entering a junction must equal the total current leaving it
100
Mean Drift Velocity
The average velocity of an electron passing through an object. It is proportional to the current, and inversely proportional to the number of charge carriers and the cross-sectional area of the object
101
Quantisation of Charge
The idea that charge can only exist in discrete packets of multiples of the elementary charge
102
Semiconductors
A material that has the ability to change its number of charge carriers, and so its ability to conduct electricity. Light dependent resistors and thermistors are both examples.
103
Diode
A component that allows current through in one direction only. In the
correct direction, diodes have a threshold voltage (typically 0.6 V) above which
current can flow
104
Electromotive Force
The energy supplied by a source per unit charge passing through the source, measured in volts
105
Filament Lamp
A bulb consisting of a metal filament, that heats up and glows to produce light. As the filament increases in temperature, its resistance increases since the metal ions vibrate more and make it harder for the charge carriers to pass through.
106
I-V Characteristics
Plots of current against voltage, that show how different components behave.
107
Kilowatt-Hour
A unit of electrical energy. It is usually used to measure domestic power consumption
108
Light-Dependent Resistor
A light sensitive semiconductor whose resistance increases when light intensity decreases
109
Negative Temperature Coefficient Thermistor
a component in which the resistance is inversely proportional to temperature
110
Ohm
The unit of resistance
111
Ohmic Conductor
A conductor for which the current flow is directly proportional to the potential difference across it, when under constant physical conditions.
112
Ohm's Law
For an ohmic conductor of constant temperature, V=IR
113
Potential Difference
The difference in electrical potential between two points in a
circuit. It is also the work done per coulomb to move a charge from the lower
potential point to the higher potential point. It is measured in Volts.
114
Power
The rate of energy transfer in a circuit. It can be calculated as the product
of the current and the potential difference between two points. It is measured in
Watts.
115
Resistance
A measure of how difficult it is for current to flow through a material
116
Resistivity
A measure of how difficult it is for charge to travel through a material.
It is proportional to the object’s resistance and cross-sectional area, and inversely
proportional to the object’s length. It is measured in Ohm metres
117
Resistor
A device that has a fixed resistance and follows Ohm’s law
118
Volt
The unit of potential difference
119
Internal Resistance
The resistance to the flow of charge within a source. Internal
resistance results in energy being dissipated within the source
120
Kirchhoff's Second Law
A consequence of the conservation of energy. The sum of the voltages must equal the sum of emfs in a closed loop
121
Lost Volts
The difference between a source’s emf and the terminal voltage. It is
equal to the potential difference across the source’s internal resistance
122
Parallel Circuit
Components are said to be connected in parallel when they are
connected across each other (separate loops)
123
Potential Divider
A method of splitting a potential difference, by connecting two
resistors in series. The total potential difference is split in the ratio of their
resistances.
124
Resistors in Parallel
The potential difference across resistors connected in
parallel is identical for each resistor. The current is split between the resistors. The
total resistance is equal to the inverse of the sum of the inverses of the
resistances of the resistors.
125
Resistors in Series
: The current through resistors connected in series is identical
for each resistor. The potential difference is split in the ratio of their resistances.
The total resistance is equal to the sum of the resistances of the resistors.
126
Sensor Circuits
A circuit that reacts to external conditions. They commonly
involve a semiconductor connected in a potential divider arrangement
127
Series Circuit
Components are said to be connected in series when they are
connected end to end (in one loop)
128
Terminal PD
The potential difference across the terminals of a power source. It is
equal to the source’s emf minus any voltage drop over the source’s internal
resistance.
129
Amplitude
A wave’s maximum displacement from its equilibrium position
130
Antinodes
A position of maximum displacement in a stationary wave
131
Coherence
Waves with the same frequency and constant phase difference
132
Constructive Interference
The type of interference that occurs when two waves
meet in phase. The wave amplitudes are superposed
133
Critical Angle
The angle of incidence that results in an angle of refraction of
exactly 90o . It is when the refracted ray travels along the boundary line
134
Destructive Interference
The type of interference that occurs when the two waves are in antiphase. When one wave is at a peak and one is at a trough their
addition results in a minimum point
135
Diffraction
The spreading of waves as they pass through a gap of a similar magnitude to their wavelength
136
Displacement
The distance that a point on a wave is from its equilibrium position
137
Electromagnetic Spectrum
The spectrum of electromagnetic waves, consisting of Gamma Rays, X-Rays, Ultraviolet, Visible Light, Infrared, Microwaves and
Radio waves
138
Electromagnetic Waves
Waves that consist of perpendicular electric and magnetic oscillations. All electromagnetic waves travel at the speed of light in a
vacuum
139
Frequency
The number of waves that pass a point in a unit time period. It is the
inverse of the time period
140
Fundamental Mode of Vibration
The oscillation of a wave at its natural
frequency
141
Intensity
The power transferred per unit area. It is proportional to the square of a
wave’s amplitude
142
Interference
The superposition of the amplitudes of waves when they meet
143
Longitudinal Waves
A wave with oscillations that are parallel to the direction of
energy propagation. Sound waves are an example of a longitudinal wave. They
cannot travel through a vacuum
144
Nodes
A position of minimum displacement in a stationary wave
145
Oscilloscope
A device used to display and analyse waveforms
146
Path Difference
A measure of how far ahead a wave is compared to another wave, usually expressed in terms of the wavelength
147
Period
The time taken for a wave to complete one full cycle
148
Phase Difference
The difference in phase between two points on a wave. It is usually expressed in radians
149
Polarisation
The restriction of a wave so that it can only oscillate in a single plane. This can only occur for transverse waves
150
Progressive Waves
Waves that transfer energy from one point to another without a transfer of matter
151
Reflection
The bouncing of a wave at a boundary. The angle of incidence will
equal to the angle of reflection
152
Refraction
The changing of speed of a wave as it passes into a new medium. If it
passes into an optically denser medium, it will slow down
153
Refractive Index
A material property that is equal to the ratio between the speed
of light in a vacuum, and the speed of light in a given material
154
Stationary Wave
A wave that stores, but does not transfer, energy
155
Superposition
When two waves meet at the same point in space their
displacements combine and the total displacement at that point becomes the sum
of the individual displacements at that point
156
Total Internal Reflection
An effect that occurs in optical fibres, where full reflection occurs at the inside boundary of the fibre, meaning no radiation passes
out. The angle of incidence must be greater than the critical angle for this to occur
157
Transverse Waves
A wave with oscillations that are perpendicular to the
direction of energy propagation. Electromagnetic waves are examples of
transverse waves
158
Wave Speed
The product of a wave’s frequency and wavelength
159
Wavelength
The distance between two identical positions on two adjacent
waves. It is commonly measured from peak to peak or trough to trough
160
Young Double-Slit Experiment
An experiment that demonstrates the diffraction of light by passing monochromatic light across two narrow slits and observing the resulting pattern of bright and dark fringes
161
Absolute Temperature
A temperature value relative to absolute zero
162
Absolute Zero
The lowest possible temperature of a system, where no heat remains and the particles in the system have no kinetic energy
163
Avogadro Constant
The number of particles that make up one mole of any gas (6.02x10^23)
164
Boltzmann Constant
A constant relating the average kinetic energy of the
particles in a gas, to the gas’ temperature
165
Boyle’s Law
The pressure of an ideal gas is inversely proportional to its volume when held at constant temperature
166
Brownian Motion
The random motion of particles
167
Change of Phase
The transitions between solids, liquids and gases. During a change of phase, there is a change of internal energy but not temperature
168
Equation of State of an Ideal Gas
:An equation linking pressure, volume, number of moles, temperature and the ideal gas constant
169
Gas
A phase of matter in which the particles are high energy and free to move.
Gases will fill the space they are placed in
170
Internal Energy
The sum of the randomly distributed kinetic and potential
energies of the particles in a given system
171
Kelvin
The unit of absolute temperature
172
Liquid
A phase of matter in which the particles can slide over each other, but still have forces of attraction between each other
173
Solid
A phase of matter in which the particles can only vibrate about fixed
positions, due to strong intermolecular forces
174
Specific Heat Capacity
The amount of energy required to increase the
temperature of 1kg of a substance by 1 Kelvin
175
Specific Latent Heat
The amount of energy required to change the state of 1kg of a substance without a change of temperature
176
Thermal Equilibrium
A stable state in which there is no thermal heat transfer
between two regions
177
Angular Velocity
An object’s rate of change of angular position
178
Centripetal Acceleration
The acceleration of an object moving in circular motion.
Any object in circular motion must have an acceleration since the direction of the
object, and therefore the velocity of the object, is constantly changing
179
Centripetal Force
The resultant force responsible for an object moving in circular
motion. Centripetal forces always act towards the centre of the object’s rotation
180
Frequency
The inverse of time period. The number of rotations per unit time
181
Period
The time taken for one whole rotation
182
Radian
A unit of angle, where 2π equal to one complete angular rotation
183
Angular Frequency
A measure of an object’s angular displacement per unit time
184
Critical Damping
The form of damping that reduces the displacement of an oscillating object to its equilibrium position in the quickest time possible and without further oscillation
185
Damping
The dissipation of energy from an oscillating system. The consequence is that the amplitude of oscillation will decrease. Damping occurs when a force opposes the system’s motion
186
Forced Oscillations
Repeated up and down oscillations, at the frequency of a driver. The amplitude of oscillation is small at high frequencies and large at low frequencies
187
Free Oscillations
Oscillations that are not caused by a driver. An object will naturally oscillate at its natural frequency
188
Isochronous Oscillator
An oscillator whose frequency is independent to amplitude
189
Natural Frequency
The frequency that a system naturally oscillates at when there is no driving force
190
Overdamping
A type of damping where the system is damped more than required to stop the oscillations. It takes longer for the system to return to equilibrium than for critical damping
191
Resonance
Resonance occurs when the frequency of oscillations is equal to the natural frequency of the oscillating system. The rate of energy transfer is at a maximum during resonance
192
Simple Harmonic Motion
Motion where the acceleration of an object is directly proportional, and in the opposite direction, to its displacement
193
Underdamping
A type of damping where energy is gradually removed from the system and the amplitude of oscillations slowly decreases
194
Escape Velocity
The minimum velocity required by an object to be able to escape a gravitational field of a mass when projected vertically from its surface
195
Gravitational Field Lines
A line representing the path that a mass would take when placed within the field
196
Geostationary Satellite
A satellite that orbits above the equator with a 24 hour period, so it will always remain above the same position on the Earth. They orbit approximately 36,000km above the surface of the Earth
197
Gravitational Field Strength
The force per unit mass exerted on a small test mass placed within the field
198
Gravitational Field
A region in space surrounding a mass in which any other object with
mass will experience an attractive force
199
Gravitational Potential Energy
The component of an object’s energy due to its
position in a gravitational field.
200
Gravitational Potential
The work done per unit mass required to move a small test mass from infinity to that point
201
Kepler’s First Law
All planets travel in elliptical orbits, with the sun at one of the foci
202
Kepler’s Second Law
All planets sweep out the same area in a given period of time
203
Kepler’s Third Law
The square of a planet's period is directly proportional to the cube of its mean distance to the sun
204
Newton’s Law of Gravitation
The force between two masses is proportional to the product of the masses involved and inversely proportional to the square of the separation of the masses
205
Capacitance
The charge stored per unit potential difference in a capacitor
206
Capacitor
An electrical component that stores charge. A parallel-plate capacitor is made of two parallel conducting plates with an insulator between them
207
Capacitors in Parallel
When capacitors are connected in parallel, their individual capacitances are summed to give the total capacitance
208
Capacitors in Series
When capacitors are connected in series, the total capacitance is equal to the inverse of the sum of the inverses of the individual
capacitances
209
Energy Stored by a Capacitor
Equal to half the product of the charge stored
and the capacitance. This can be found from the area under a charge-voltage graph
210
Farad
The unit of capacitance
211
Time Constant
The product of the circuit resistance and capacitance. It is the
time taken for the voltage to discharge to 1/e (or 36.8%) of its initial charge
212
Coulomb’s Law
The size of the force that acts between two point charges is proportional to the product of their charges and inversely proportional to the square of their separation. It is attractive for opposite charges and repulsive for
like charges
213
Electric Field Strength
The force per unit positive charge exerted on a charged object placed at that point in the field. This is a vector acting in the same direction as the force on a positive charge
214
Electric Field
A region surrounding a charged object which causes a force to be exerted on any charged object placed within the field
215
Electric Potential Energy
The work done on a positive charge in bringing it from infinity to that point in the field. It is proportional to the product of the two charges and inversely proportional to their separation
216
Electric Potential
The work done per unit charge on a positive test charge in bringing it from infinity to that point in the field
217
Electric Field Lines
Lines that demonstrate the direction in which a positive test charge would go if placed at that point in the field
218
Parallel Plate Capacitor
A capacitor made up of two parallel conducting plates with an insulator between them
219
Permittivity
A property of an electric field. It relates electric flux density and the electric field strength
220
Faraday’s Law
The magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linkage
221
Magnetic Field Lines
Lines that show the direction in which a magnetic North monopole would experience a force if placed at that point in a field. Magnetic field lines point from North to South
222
Fleming’s Left-Hand Rule
The relative direction of motion, field direction and current direction in the motor effect can be represented by the thumb, first finger and second finger of the left hand respectively. For the motion of a charged
particle in a magnetic field, its direction replaces the current direction
223
Force on a Charge Particle
A charged particle moving through a magnetic field will experience force equal to the product of the charge, its velocity and the
magnetic flux density
224
Force on a Current-Carrying Conductor
A current-carrying conductor will experience a force when placed in a magnetic field. The direction of the force can be determined using Fleming’s left-hand rule
225
Lenz’s Law
The direction of an induced current is such that it opposes the current that created it
226
Magnetic Field
A region of space in which magnetic materials and moving electric charges feel a force
227
Magnetic Flux Density
The force per unit current per unit length on a
current-carrying wire placed at 90º to the field lines. Sometimes also referred to as the magnetic field strength
228
Magnetic Flux Linkage
The magnetic flux multiplied by the number of turns, N, of the coil
229
Magnetic Flux
A value which describes the magnetic field or field lines passing through an area. It is the product of magnetic flux density and the perpendicular area it passes through
230
Tesla
The unit of magnetic flux density
231
Transformer
A device used to increase or decrease the voltage with two sets of coils with different numbers of turns wrapped around a magnetic core. The transformer is step-up if the number of coils on the secondary coil is greater than the number on the primary coil. The transformer is step-down if the number of coils on the secondary coil is fewer than the number on the primary coil
232
Velocity Selector
A combination of a magnetic field and an electric field, which
results in charges passing through and leaving with a specific velocity
233
Weber
The unit of magnetic flux
