AS Content Flashcards
1
Q
What is the photoelectric effect?
A
When a certain frequency of light is shone onto different types of metals, the photons individually interact with the electrons in the metal causing them to gain enough energy to be released from the metal.
2
Q
What is threshold frequency?
A
The minimum required frequency needed to be shone onto a metal for it to start emitting electrons.
3
Q
What is the ’work function’?
A
The required energy needed to release an electron from a metal.
4
Q
How does the work function change with the reactivity of a metal?
A
Generally, more reactive metals have a lower work function.
5
Q
What is the equation for photon energy in photoelectric emission?
A
Photon energy = work function + kinetic energy of electron
6
Q
What is stopping voltage?
A
The voltage necessary in a potential divider circuit to make the photocurrent zero
7
Q
What is Plancks constant? (Value)
A
6.63x10^-34m
8
Q
What is de broglie’s wavelength function?
A
Lambda = h (Planck constant) / p (momentum)
9
Q
What is the equation for momentum? (Derived from the electron gun experiment)
A
P = sqrt( 2 x Ek x m )
10
Q
What is the relation between wavelength and kinetic energy?
A
Lambda (wavelength) ∝ 1 / sqrt(Ek)
11
Q
Def a photon
A
A photon is a quantum of EM radiation (like in cs with processes getting a quantum of runtime)
12
Q
What is the equation for the energy of a photon?
A
E = (h (Planck constant) x c) / lambda (wavelength)
Or E= hc/lambda
13
Q
What is the equation for the electron volt?
A
eV = (1/2)mv^2 where e is the elementary charge and V is voltage but v is velocity and m is mass
14
Q
What is the name for an electron that has been released from a metal due to the photoelectric effect?
A
Photoelectrons
15
Q
What two pieces of evidence show that light is a wave?
A
Light produces interference patterns and can also be diffracted which are only explained by light being a wave and following superposition.
16
Q
What was de broglies suggestion about electrons behaving like waves?
A
If ’wave-like’ light showed particle properties, then ’particles’ such as electrons should be expected to show wave light properties
17
Q
What experiment proved de broglie right about electrons behaving like waves?
A
The electron diffraction experiment
18
Q
The equation for current in terms of charge including units
A
I = Q(coulombs) / T(seconds)
19
Q
What is the value of the elementary charge e?
A
e = 1.6x10^-19 C
20
Q
What two things could cause an increase in rate of charge flow?
A
More electrons passing through a given point (greater cross sectional area)
The same number of electrons electrons moving faster through the wire
21
Q
What is Kirchhoff’s first law?
A
The sum of the currents into a junction is equal to the sum of the currents leaving the junction
22
Q
How are materials classified by conductivity?
A
Their number density (number of free electrons per cubic meter)
23
Q
What are the three categories of conductivity of material?
A
Insulators, semiconductors, conductors
24
Q
What is the equation for current in terms of mean drift velocity?
A
I = Anev where A is cross sectional area in meters squared and v is velocity in ms
25
How does reducing the cross sectional area of a wire affect the drift velocity if flow of charge remains constant?
The drift velocity increases in the smaller area to compensate
26
What is Kirchhoff’s second law?
The sum of the e.m.f.s is equal to the sum of the p.d.s in a closed loop
27
What can Kirchhoff’s second law be broken down to? (Interpreted as)
The total energy transferred to the charges in a circuit is always equal to the total energy transferred from the charges as they move around the circuit.
28
How is current affected by components in a series circuit?
It isn’t, it is the same all the way round
29
What is the sum of the p.d. Across components in a circuit equal to?
The e.m.f. (Components with more resistance get a higher share of the voltage)
30
In a parallel circuit, how much of the current will a branch with twice the resistance of another branch receive?
Half of the current
31
How does Kirchhoff’s second law work in parallel circuits?
The sum of the e.m.f. Is equal to the sum of the p.d. of all the components in that closed loop (branch of the parallel circuit)
32
What does a power source need in order to output a high current?
A low internal resistance, such as a car battery
33
How is energy ‘lost’ in the cell of an electrical circuit?
Energy is ‘lost’ to heat as work has to be done by the charge carriers in the power source, for a chemical source, this is due to reactions between chemicals.
34
What is terminal p.d.?
The p.d. measured at the terminals of a power source
35
How does terminal p.d. differ from e.m.f.?
The terminal p.d. Is lower than the actual e.m.f. due to energy lost from internal resistance, these are called lost volts.
36
What is the equation for e.m.f. in terms of terminal p.d.?
Electromotive force = terminal p.d. + lost volts
37
How does an increase in current affect terminal p.d. and lost volts when the emf remains constant?
And increase in current means more charge carriers doing work in the cell which increases lost volts and decreasing terminal p.d.
38
What is the equation for lost volts?
V (Lost volts) = I (current) x r (internal resistance)
39
What’s the equation for emf from a power source (derived from e = v + lost volts)
emf = V (terminal p.d.) + I (current) x r (internal resistance) or emf = I (current) x (R (resistance) + r (internal resistance))
40
What is Kirchhoff’s second law?
The sum of the e.m.f.s is equal to the sum of the p.d.s in a closed loop
41
What is the equation for potential difference in terms of charge?
V = W(energy transferred) / Q(charge)
42
What property would an ideal voltmeter have in order to function most efficiently?
It would have infinite resistance so when connected, no current would actually pass through
43
Define voltage in terms of work done by the charge carriers
Voltage is work done *by* the charge carriers, thus, the charge carriers are *losing* energy as they pass through components
44
Def electromotive force? (e.m.f.)
e.m.f. Is when work is done *on* the charge carriers, essentially the charge carriers gain energy as they travel through a component such as a cell, battery or power pack
45
What is the equation for the electromotive force?
E (e.m.f.) = W (energy transferred) / Q (charge)
46
What is the name of the process when electrons gain enough energy to escape the surface of a metal?
Thermionic emission - the emission of electrons through the action of heat
47
How does an electron gun work?
A heated filament is placed in a vacuum and a high p.d. Is applied between the filament and an anode, the filament then acts as a cathode and the freed electrons accelerate towards the anode gaining kinetic energy as they go. The electrons then go through a small hole in the anode creating a beam of electrons with a specific kinetic energy
48
What is the equation for calculating the work done on a single electron travelling from the cathode to the anode in the electron gun experiment? (Hint, not kinetic energy)
W (work done) = e x v (accelerating p.d.)
49
What is the equation for the work done on an electron to increase its kinetic energy?
eV (work done on an electron) = 1/2 x m (mass) x v^2 (velocity)
50
What assumption is being made when calculating the work done on an electron to increase it’s kinetic energy (in the electron gun experiment)
The electrons have negligible kinetic energy at the cathode (initial energy is almost 0)
51
How does increasing the accelerating p.d. In the electron gun experiment affect the velocity of the electrons?
It increases the kinetic energy (more energy being transferred *to* the electrons) so they have a greater velocity.
52
What is the equation for resistance?
R (resistance) = p.d. (Voltage) / Current
V = IR
53
What is the definition of an ohm?
The resistance of a component when a p.d. of 1 is produced per amp of current
54
What is Ohm’s law?
For a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the p.d. across its ends.
55
Why does resistance increase when heat increases?
When heat increases, the positive ions in the metal gain more energy thus vibrate more about their mean positions so the frequency of collisions between the positive ions and charge carriers increases so the charge carriers do more work (transfer more energy) as they travel through the wire.
56
What does the I-V graph for a fixed resistor look like?
Straight line through the origin
57
What is a resistor called if it obeys ohms law?
It is an ohmic conductor.
58
How does a resistor behave under reversed polarity?
The same
59
What is the relationship between the voltage and current in a filament lamp I-V graph and what does this say about the lamp?
Voltage is not directly proportional to current so is a non ohmic conductor and its resistance is not constant.
60
How does the behaviour of a filament lamp change with polarity?
It behaves the same
61
What is a main reason that LEDs are more effective than other bulbs?
They do not get hot so do not have much resistance and draw much less power
62
What does the I-V graph of a diode look like?
Flat up until the origin where it starts to curve upwards before increasing at a linear rate
63
What is the relationship between the p.d. and current in an LED and what does this say about and LED?
P.d. Is not directly proportional to current in an LED and so can be described as a non ohmic conductor
64
How does the behaviour of an LED change with polarity?
A negative voltage will cause an infinite resistance in the LED so it will not work
65
What is the name of the point on an I-V graph for an LED where the resistance starts to decrease?
The threshold p.d.
66
What three factors (aside from temperature) affect resistance?
The material
The length of the wire L
The cross-sectional area of the wire A
67
What is the relationship between Resistance and the length of a wire?
Resistance is directly proportional to the length of a wire (double R = double L)
68
How is resistance related to cross-sectional area?
Resistance is inversely proportional to cross sectional area (2R = 1/2A)
69
What is the equation for resistivity?
R (resistance) = (P (resistivity) x Length) / A (cross-sectional area)
70
What does it mean if a material has a negative temperature coefficient?
It’s resistance drops as the temperature increases
71
What is a thermistor made of?
A material with a negative temperature coefficient
72
Where are thermistors used?
Thermometers
Thermostats
Engine temperature monitors
73
What does the I-V graph for a thermistor look like?
It is an upwards curve (downwards cure in the negative V)
74
How does the resistance of an LDR change with surrounding conditions?
As the surroundings get brighter, resistance decreases
75
How does an LDR work?
When the light intensity increases, the resistance decreases because the number density of charge carriers increases.
76
Define potential difference
The amount of work done per unit charge
77
Define the volt
The potential difference across a component is 1 volt when you do 1 joule of work moving 1 coulomb of charge through a component
78
Define mean drift velocity
The average velocity of all the charge carriers
79
What are the charge carriers in liquids and gasses?
Ions
80
What does the IV graph for a thermistor look like?
It is an upward curve in the top right and a downward curve in the bottom left
81
Define Power in terms of an electrical circuit
Power is the rate of energy transfer
82
What are 2 equations for electrical power?
P = W (work done in watts) / T (time)
P = VI
83
What is the equation for work done in terms of power?
W = Power x Time
Also, W = VIT (voltage x current x time)
84
When working with power, what should you always look out for?
Of the units, most questions deal with kWh but some only Wh
85
What causes resistance?
Electrons collide with atoms and lose energy
86
How do you calculate the total e.m.f. for cells in series?
Add together the individual e.m.f.s of all the cells in parallel
87
How do you calculate the total e.m.f. for identical cells in parallel?
total e.m.f. will equal the e.m.f. of the individual cells (e = e1 = e2 etc)
88
How can you measure terminal p.d?
Attach a voltmeter to the power supply terminals. This will be just slightly less than the e.m.f. due to lost volts.
89
What is the equation to calculate output voltage in a potential divider circuit? And which resistor is the output attached to?
Vout = (R2 x Vin) / (R1 + R2) where R2 is the resistor connected in parallel with a voltmeter
90
What is a potentiometer?
A potentiometer is a potential divider that uses a variable resistor instead of R1 and R2
91
What ratio describes the distribution of p.d in a potential divider circuit? Explain what it means
V1 / V2 = R1 / R2. If a component has a higher resistance then it will receive a higher share of the voltage. Or, the greater the share of the total resistance, the greater the p.d supplied.
92
What is the name for forces that produce an extension in an object?
Tensile forces
93
What is the name for forces which compress an object?
Compressive forces
94
What happens to a spring when it experiences tensile and compressive forces?
Tensile deformation
Compressive deformation
95
What happens to the force-extension graph of a spring when it reaches its elastic limit? And what does the spring experience past this point?
It starts to flatten out and experience plastic deformation
96
What is elastic deformation?
When the shape of an object is deformed but it will still return to its original shape
97
What is plastic deformation?
When the shape of an object is deformed but it will not return to its original shape
98
When does a spring generally obey Hooke’s law?
When it has not yet reached its limit of proportionality.
99
What is the equation for force in terms of extension? (Hooke’s law)
Force = spring constant x extension
100
What is the spring constant of a spring actually measuring?
The stiffness of a spring
101
How can the spring constant be interpreted?
If the spring constant is high, the spring is difficult to extend
102
What is the gradient of a force - extension graph?
The spring constant
103
What happens to the work done on a material that is extended?
If it has not gone beyond its elastic limit, the work done on a material that is extended can be fully recovered
104
What is the equation for work done in a material that has been extended?
Change in W = Force x Change in distance
105
What is the area under a force - extension graph?
The work done on the spring
106
What is the work done on a spring in order to extend it transferred into?
Elastic potential energy within the spring
107
What is the equation for elastic potential energy and where has it come from?
E = 1/2 * F * extension
This is the area under a force extension graph since it will be a triangle
108
What is the equation for elastic potential energy in terms of the spring constant?
E = 1/2 * k * extension^2
109
What will doubling the extension of a spring do to its elastic potential energy? Why?
Multiply it by 4, since elastic potential energy is directly proportional to extension^2
110
What is the name of the ‘loop’ formed under the force-extension graph of rubber?
A hysteresis loop.
111
What does the area inside of a hysteresis loop represent?
The thermal energy released in the loading of the rubber material.
112
What is the equation for tensile stress?
Stress = force / cross-sectional area
113
What is the equation for tensile strain?
Strain = Extension / original length
114
What is it called when a material is stretched and begins to get thinner?
Necking
115
What are the 6 major points on a stress strain graph (for steel)? (In order)
The limit of proportionality
The elastic limit
Yield points 1 and 2
UTS point
Breaking point
116
What is the limit of proportionality?
The point when a material stops obeying Hooke’s law
117
What could define a strong material?
One with a high ultimate tensile strength
118
What is the equation for young modulus?
Young modulus = Stress / strain
119
When does the young modulus apply?
Up to the limit of proportionality of a material
120
What is the unit for the young modulus?
Pa or Nm^-2
121
How can you obtain the young modulus of a material from its stress strain graph?
By finding the gradient
122
How can young modulus be interpreted?
A higher young modulus makes for a stiffer material
123
How can you identify a brittle material from a stress strain graph?
A brittle material does not have a curve, the line simply ends when the material snaps
124
What is the elastic limit?
The point at on a force-extension graph where if exceeded, a spring will no longer return to its original shape
125
What is the equation for spring constant in a series of springs?
1/k = 1/k1 + 1/k2 (the same equation for resistance in parallel)
126
What is the equation for spring constant for springs arranged in parallel?
K = k1 + k2
127
What is the ultimate tensile strength of a material?
The maximum amount of stress it can endure before necking and breaking
128
How can you measure the young modulus of a wire?
Stretch it between to points and mark its length at any point, then find the cross sectional area and total length of the wire. Then add weights to one end and as the wire stretches measured its new weight with each new mass added. Then calculate with this the stress and strain then the young modulus.
129
What is the unit for stress?
Nm^-2
130
What is the unit for strain?
There isn’t one
131
Def conservation of energy
The total energy of a closed system remains constant. Energy cannot be created or destroyed, only transferred from one form to another.
132
Define energy
The capacity that something has to do work (since one Joule is equal to one Nm)
133
Def elastic potential energy
The energy stored in an object as a result of reversible changes in its shape
134
Def electrical potential energy
Energy of electric charges due to their position in an electrical field
135
Def internal (heat or thermal) energy
The sum of all the random potential and kinetic energies of the atoms in a system
136
What is important to remember about KE and GPE which is useful in an exam?
Loss of GPE = gain in KE, therefore:
mgh = 1/2mv^2 (Cancel the mass)
137
What is the equation for power?
P = W / t
138
What other ways could you find the work done in the power equation?
Find the change in kinetic energy,
Find the change in GPE
Find the regular work done (force x distance)
139
What is the second equation for power? (In terms of speed)
Power = force x speed
140
What is the equation for efficiency percentage?
Efficiency = (useful output energy / total input energy) x 100
141
What is the main equation for work done?
W = force x distance
142
Define the centre of mass
The centre of mass of an object is the mean point of all the mass of an object
143
Define the centre of gravity and where is it?
The centre of gravity is the point where the entire weight of an object can be thought to be concentrated. (Appears to act). It is in the same place as the centre of mass.
144
How can you find the centre of gravity of an object?
By using 2 points of suspension on a 2D object (flat object) you can use a plumb line to draw a vertical line across the object. The point of intersection of these two lines is the centre of gravity.
145
What are the 6 main forces to be considered in almost any free-body diagram?
Weight
Friction
Drag
Tension
Upthrust
Normal
146
What are the two main factors in causing an objects terminal velocity?
The objects speed and cross-sectional area
147
What is drag directly proportional to?
Speed^2
148
What is the equation for the moment of an object?
Moment = force x distance perpendicular to the direction of the line of action of the force
149
What is the unit for a moment?
Nm (Newton metre)
150
Define a couple of forces
When two equal forces parallel to each other but on different lines that are of equal magnitude affect two different sides of an object causing it to spin without moving (rotating and not translating)
151
What is the torque of a couple?
The torque of a couple is the moment between the pair of forces
152
What is the equation for the torque of a couple?
Torque (Nm) = Force (N)(of one of the forces) x distance (m)(between the two forces not the centre)
153
What needs to be included alongside the answer and units for a question that wants the torque of a couple?
The direction of motion of the torque (clockwise or anti-clockwise)
154
What is an easy way to help visualise and thus solve a triangle of forces question?
Draw the completed triangle of forces
155
What is the equation for pressure? (Basic)
P = F / A
156
What is the unit for pressure and what is its unit in SI units?
Pascals (Pa) or (Nm^-2)
157
What is the equation for the pressure of a vertical column of liquid?
P = height x density x g
158
What unusual property is true about the pressure in a fluid?
The pressure at any particular depth is the same in all directions.
159
What is the equation for the upthrust of an object underwater and how is this obtained?
Upthrust = x (depth of the object) * cross sectional area * density of the fluid * g
This is obtained by subtracting the pressure acting at the top of any object from the pressure acting at the bottom of the object. This is what gives x as distance and not depth since x is the distance between the two places that the pressure is being measured.
160
What is the Upthrust of an object in a fluid equal to?
The weight of the the fluid displaced by the object
161
What is archimedes principle?
The Upthrust exerted on a body immersed in a fluid wether fully or partially submerged is equal to the weight of the fluid that the body displaces.
162
What could you change in the ball and tube of liquid experiment to affect the balls terminal velocity? (4)
Change the liquid
Change the size of the ball
Change the shape of the item being dropped
Change the mass of what’s being dropped
163
What is Archimedes principle?
When a body is partially or fully submerged in a fluid, it experiences an upthrust equal to the weight of the fluid displaced
164
What is newton’s 1st law?
An object will continue to move with constant velocity or remain at rest unless a resultant force acts upon it.
165
What is Newton’s second law of motion?
The rate of change of momentum is directly proportional to the force acting on an object
166
What is Newton’s 3rd law of motion?
If object A exerts a force on object B, object B will exert an equal and opposite reaction force on object A, where both forces are of the same type and are along the same line.
167
What is the unit for momentum?
Kgms^-1
168
What is the unit for impulse?
Ns
169
What’s the equation for momentum (use the generally accepted symbols)
P = mv
170
What is the law of the conservation of momentum?
Momentum is conserved in any collision provided that no external force acts on the objects.
171
What is the area under a velocity-time graph?
Displacement (not distance!)
172
What are thinking distance, breaking distance and stopping distance?
Thinking - The time from seeing the obstacle and applying the breaks
Breaking - The time from applying the breaks to coming to a complete stop
Stopping - The time from noticing the obstacle to coming to a complete stop
173
What is the equation for thinking distance?
Thinking distance = speed x reaction time
174
Give the two main practical ways of finding the speed of gravity in a lab
Using electromagnets and a timer
Using light gates
175
What does the gradient of a displacement-time curve look like when an object is decelerating?
It is curving downwards
176
How do you get velocity from a displacement time graph?
Find the gradient. Remember v is the differential of s and a is the differential of v
177
What 4 things can affect thinking distance?
Tiredness
Alcohol/drugs
Illness
Distractions such as children
178
What 3 things can affect breaking distance?
Bad brakes so reduces friction
Wet or icy roads (anything reducing the tyres friction with the road)
The weight of the car (a lighter car has less momentum)
179
define a progressive wave
A moving wave that carries energy from one place to another without transferring any material in which the direction of energy transfer is the same as the waves direction of travel
180
def phase difference
The amount that one wave lags behind another
181
What is the equation for frequency in terms of the period?
Frequency = 1 / Period
182
How does an oscilloscope work?
A cathode ray oscilloscope measures voltage. It displays waves from a signal generator as a function of voltage over time.
183
What is the name of the wave on an oscilloscope?
A trace
184
What are the squares on an oscilloscope called?
Divisions
185
What is the timebase on an oscilloscope?
The horizontal axis is the timebase (the amount of time per division)
186
How would you calculate wave frequency from an oscilloscope?
Find the period by counting how many divisions in one full oscillation of the wave and then multiply by the timebase. Then do 1 / Period to get frequency.
187
What two dials are on an oscilloscope and can help make them easier to read?
The gain dial (changes volts/div) and the timebase dial (changes time(ms)/div)
188
What direction do transverse waves vibrate with respect to the direction of movement?
At right angles to the direction of movement
189
What direction do longitudinal waves vibrate with respect to the direction of movement?
Parallel to the direction of movement
190
What is the name for the points on a longitudinal wave where the waves are close together and far apart?
Compression (close) and rarefaction (far)
191
How can you identify the wavelength of a longitudinal wave?
From one compression/rarefaction to another
192
Define the intensity of a wave
Intensity is the rate of flow of energy per unit area at right angles to the direction of travel of the wave
193
What is the equation and unit for wave intensity?
Intensity (W/m^2) = Power (W) / Area (m^2)
194
Intensity is proportional to...
Amplitude squared
195
What types of fields are the waves on the EM spec
Electrical and magnetic
196
Can EM waves be polarised?
Yes, since they are all transverse
197
What is the full EM spec?
Radio, Micro, Infrared, Visible light, Ultraviolet, X-Ray, Gamma
198
What is the approximate wavelength of radio waves? (m)
10^-1 - 10^6
199
What is the approximate wavelength of microwaves? (m)
10^-3 - 10^-1
200
What is the approximate wavelength of infrared light? (m)
7x10^-7 - 10^-3
201
What is the approximate wavelength of visible light? (m)
4x10^-7 - 7x10^-7
202
What is the approximate wavelength of ultraviolet light? (m)
10^-8 - 4x10^-7
203
What is the approximate wavelength of X-rays? (m)
10^-13 - 10^-8
204
What is the approximate wavelength of gamma rays? (m)
10^-16 - 10^-10
205
What are some uses of radio waves? (1)
Radio transmmissions
206
What are some uses of microwaves? (3)
Radar, cooking, TV transmissions
207
What are some uses of infrared light? (4)
Heat detectors, night vision cameras, remote controls, optical fibers
208
What are some uses of visible light? (2)
Human sight, optical fibers
209
What are some uses of ultraviolet light? (2)
Sunbeds, security marks
210
What are some uses of X-rays? (3)
Medical imaging, Airport security scanners, radiotherapy (cancer treatment)
211
What are some uses of gamma rays? (3)
Irradiation of food, sterilization, radiotherapy (cancer treatment)
212
What can radio waves penetrate through?
Matter
213
What can microwaves penetrate through?
Mostly matter, but causes heating
214
What can IR light penetrate through?
Absorbed by matter but causes heating
215
What can visible light penetrate through?
Absorbed by matter but causes heating
216
What can UV light penetrate through?
Absorbed by matter but causes some ionisation
217
What can X-rays penetrate through?
most matter but causes ionisation
218
What can gamma rays penetrate through?
most matter but causes ionisation
219
def polarisation
The filtering of transverse waves so that they only pass through a filter if they oscillate in one direction (are able to pass through the filter)
220
def the plane of polarisation
The plane which a polarised wave oscillates on (a vertical filter polarises a wave in the vertical plane)
221
def plane polarisation
When a wave is polarised to only oscillate in one direction
222
What does the fact that you can polarise light show that light is?
It shows that light is a wave (or rather behaves like one)
223
What is the transmission axis of a polarisation filter?
Only light oscillating along the transmission axis will pass through (Waves oscillating vertically will be transmitted through a vertical transmission axis)
224
What can you use to polarise microwaves?
A metal grille (microwaves have too high a wavelength to be polarised through a polarisation filter)
225
What determines how much waves diffract through a gap?
The size of the gap and the wavelength of the travelling wave.
226
At what point can you observe the most diffraction when changing the size of the gap in an experiment?
When the size of the gap is the same as the wavelength of the travelling wave.
227
What happens if the size of a gap for diffraction is smaller than the wavelength?
The waves get reflected back on themselves
228
Why can you hear someone round a doorway but not see them?
Sound waves have similar wavelengths to the size of doorways and so diffract a lot but light waves are far too small to cause noticeable diffraction
229
What two experiments could you do to show light diffracting?
Shine a laser through a very small slit or shine white light through a colour filter.
230
def reflection
When a wave is bounced back upon hitting a boundary where the angle4 of incident is equal to the angle of reflection.
231
def refraction
The change in the direction of movement of a wave as a result of entering a different medium.
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Why does the wave speed change during refraction?
The wavelength changes but the frequency remains constant.
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def optical density
The amount that a material slows down light. A higher optical density means light travels slower through it.
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what is the equation for refractive index?
n (refractive index) = c (sol in a vacuum) / v (sol in that material)
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What is Snell's law
n1sinA1 = n2sinA2
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def total internal reflection
When all of the light is reflected back into the material and not refracted
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What is a critical angle? (refraction)
The angle at which light stops being refracted and is only internally reflected if it gets any larger
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What is the equation for the critical angle for light within a material to air boundary?
SinC = 1/n
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def superposition
When to waves cross, the displacement as any point is the sum of the two individual displacements
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def interference
When two or more waves superimpose with each other
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def constructive interference
When waves 'combine' to increase the original displacement. i.e. a crest and a crest or a trough and a trough
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def destructive interference
When two waves superimpose at a point to create nothing i.e. a crest 'combines' with a trough of equal size and results in 0 displacement
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what does it mean if interference isn't 'total'?
The two parts of the waves are not of equal magnitude and so don't completely cancel out or completely double in displacement.
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def 'in phase'
two points on a wave are in phase if they are at the same point of the wave cycle i.e. two crests
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what property to points that are in phase have?
The same displacement and velocity
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def phase difference?
The difference in position (x-axis) of two points
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def coherence
When two waves have the same wavelength and frequency and a fixed phase difference
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def path difference
For two wave sources that are in phase and coherent, the path difference is just how much further one wave has travelled compared to another to get to that point.
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At what amount of path difference can you observe constructive interference?
When the path difference is a whole number of wavelengths
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At what amount of path difference can you observe destructive interference?
When the path difference is an odd number of half wavelengths.
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What is the equation for wavelength that links fringe spacing and the distance from a slit to a screen?
λ = (a (slit separation) * x (fringe separation)) / D (distance from slits to screen)
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What effect does diffracting through more than two slits have in comparison to diffracting through only two slits?
The fringes are brighter and more defined (narrower).
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When shining light through a diffraction grating, what effect does a longer wavelength light cause?
The pattern will be more spread out
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What happens when white light is shone through a diffraction grating?
Each maxima (order) is a spectra from red on the outside (side furthest from central maxima) and violet on the inside (side closest to central maxima)
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Do stationary waves transmit energy?
Nuh uh
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How is a stationary wave formed when only one signal generator is present?
The waves generated travel out and then reflect back perfectly to create a standing wave
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On a standing wave, where are the nodes and where are the antinodes?
Nodes are where the waves meet, antinodes are where the waves are at a greatest distance.
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Define resonant frequency in terms of a number of wavelengths.
In order to achieve a resonant frequency, an exact number of half wavelengths fit into the space that a wave has to oscillate. Or in the string experiment, an exact number of half wavelengths fit onto the string.
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If a tube is open at both ends and a standing wave is within it, what type of node would be at each end?
Antinode
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If a tube is closed at both ends and a standing wave is within it, what type of node would be at either end?
Node
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What is the area under a force-time graph equal to
The impulse
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What happens to energy and momentum in a perfectly elastic collision?
Momentum and kinetic energy are both conserved. I.e. no energy is dissipated as heat or sound
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What happens to energy and momentum in an inelastic collision?
Some kinetic energy will be converted to other forms during the collision but momentum is still conserved
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What is the point of air bags, crumple zones and seatbelts in a collision?
They slow you down gradually, therefore reducing the change in momentum (impulse) that you experience
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Why are seatbelts risky in some cases? (2)
They can cause bruising during a crash
They can be dangerous for small children and if the seatbelt is seated at their neck can be fatal
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Why are airbags risky during a crash in some cases?
If not wearing a seatbelt, a passenger can hit a rapidly expanding airbag very quickly and can be seriously injured by the bag.
For a rear facing booster seat, an airbag can push the seat towards the car seat with a lot of force and kill the child
