1
Q
What is the value of the prefix T (tera)?
A
10¹²
2
Q
What is the value of the prefix G (giga)?
A
10⁹
3
Q
What is the value of the prefix M (mega)?
A
10⁶
4
Q
What is the value of the prefix k (kilo)?
A
10³
5
Q
What is the value of the prefix d (deci)?
A
10⁻¹
6
Q
What is the value of the prefix c (centi)?
A
10⁻²
7
Q
What is the value of the prefix m (milli)?
A
10⁻³
8
Q
What is the value of the prefix μ (micro)?
A
10⁻⁶
9
Q
What is the value of the prefix n (nano)?
A
10⁻⁹
10
Q
What is the value of the prefix p (pico)?
A
10⁻¹²
11
Q
What six base units of the SI system are used in A Level Physics?
A
metre, kilogram, second, Ampere, Kelvin, Mole
12
Q
What six base quantities of the SI system are used in A Level Physics?
A
length, mass, time, electric current, absolute temperature, amount of substance.
13
Q
What is the base unit of mass?
A
kg
14
Q
What is the base unit of length?
A
m
15
Q
What is the base unit of time?
A
s
16
Q
What is the base unit of current?
A
A
17
Q
What is the base unit of absolute temperature?
A
K
18
Q
What is the Unit of potential difference?
A
V
19
Q
What are the Units of density?
A
kgm⁻³
20
Q
What is the SI unit of energy?
A
J
21
Q
What is the SI unit of power?
A
W
22
Q
What is the SI unit of charge?
A
C
23
Q
What units are equivalent to the volt?
A
JC⁻¹
24
Q
What base units are equivalent to the Newton?
A
kgms⁻²
25
What base units are equivalent to the Joule?
kgm²s⁻²
26
What units are equivalent to the Pascal?
Nm⁻²
27
What are the units of momentum?
kgms⁻¹
28
What are the units of resistivity?
Ωm
29
What units are equivalent to a Watt?
Js⁻¹
30
What are the units of angular velocity (ω)?
rad. s⁻¹
31
What is 1m² in mm²?
10⁶mm²
32
What is 1m³ in cm³?
10⁶cm³
33
What is 1km² in m²?
1x10⁶m²
34
What is 1cm³ in mm³?
10³mm³
35
There are 10²⁴ free charge carriers per m³ of a material. How many are there per mm³?
10¹⁵
36
10⁶ particles strike each mm² of a surface per second. How many strike 1m² of the surface per second?
10¹²
37
If there is 1 particle per mm³, how many are there per m³?
10⁹
38
Water has a density of 1000kgm⁻³. What is this in kgcm⁻³?
10⁻³
39
Water has a density of 1000kgm⁻³. What is this in gcm⁻³?
1
40
What is a control variable?
Something that must be kept constant to prevent it affecting the dependent variable
41
What is meant by the repeatability of results?
Similar results would be obtained from repeats of the same measurement from the same experimental set up.
42
What is meant by the reproducibility of results
Similar results would be obtained from repeats by different people with different equipment.
43
How can you ensure a metre rule is held vertically?
Use a plumb line, set square or spirit level
44
How do you avoid parallax error?
Ensure eye, object and scale are all in line with each other OR ensure object and scale are directly adjacent to each other
45
What is meant by the term random error?
Errors that cause the measurement to vary in unpredictable ways.
46
What is a systematic error?
An error that causes the measurements to differ from the true value by a consistent amount.
47
What is a zero error?
An error that occurs due to the measuring instrument reading a non-zero reading when the measured quantity is zero.
48
What is meant by the accuracy of a result?
How close a measurement is to the 'true' or accepted value
49
What is meant by the precision of results?
How close repeated measurements are to each other.
50
What is meant by the resolution of a measuring instrument?
The smallest change in quantity that can be measured.
51
What determines the resolution when using a multimeter?
The scale selected.
52
What is the resolution of a metre rule?
1mm
53
What is the resolution of vernier calipers?
0.1mm
54
What is the resolution of a micrometer
0.01mm
55
How do you find the absolute uncertainty from repeated readings?
± ½ the range of the repeats
56
How do you estimate uncertainty when repeated results are identical?
± ½ the resolution of the instrument
57
How do you calculate percentage uncertainty?
(Absolute uncertainty ÷ 'calculated OR measured' value) × 100
58
What do you do to the uncertainties when quantities are added or subtracted?
The absolute uncertainties are added together
59
What do you do to the uncertainties when quantities are multiplied or divided?
The percentage uncertainties are added together
60
What do you do to the uncertainties when a quantity is raised to a power?
The percentage uncertainty is multiplied by that power
61
How do you find the uncertainty in a gradient?
± (gradient of the line of best fit − gradient of the line of worst fit)
62
What is a line of worst fit?
The steepest or shallowest line that passes through the error bars.
63
What are error bars?
Lines to show the range of the absolute uncertainty of each data point on a graph
64
How do you find uncertainty in a y-intercept?
± (y-intercept of the line of best fit − y-intercept of the line of worst fit)
65
What is a charge carrier?
A charged particle capable of transferring electric current.
66
What do we mean when we say charge is quantised?
It can only take certain values (always ne)
67
If n electrons are removed from a neutral object what is its charge?
ne
68
What is an electrolyte?
A liquid containing charged ions.
69
What is a metallic conductor?
A material comprising a lattice of positive ions and delocalised electrons that carry electrical current
70
Which direction does conventional current flow?
From positive to negative.
71
Which direction do electrons flow in a circuit?
From negative to positive.
72
What is an ion?
A non-neutral atom or molecule.
73
What is a cation?
A positively charged ion
74
What is an anion?
A negatively charged ion.
75
What is an anode?
A positive electrode.
76
What is a cathode?
A negative electrode.
77
How is an ammeter connected?
In series
78
What is the resistance of an ideal ammeter?
Zero.
79
State Kirchoff's first law.
At any point in a circuit the sum of the currents entering that point is equal to sum of the currents leaving.
80
What is n in the equation I = nAve and what are its units?
Number density of free charge carriers m⁻³
81
What is A in the equation I = nAve?
Cross-sectional area of the conductor.
82
What is e in the equation I = nAve?
The elementary charge (1.6x10⁻¹⁹C)
83
What is v in the equation I = nAve?
The drift velocity of the charge carriers.
84
What is a conductor?
A material with a large number density of charge carriers ~10²⁸m⁻³
85
What is an insulator?
A material with a low number density of charge carriers.
86
What is a semiconductor?
A material with an intermediate number density of charge carriers ~10¹⁷m⁻³
87
What is potential difference?
The work done per unit charge between two points
88
What is the SI unit for potential difference?
Volt (V)
89
What units are equivalent to the volt?
Joules per Coulomb (JC⁻¹ )
90
What is EMF (Electromotive force)?
The work done per unit charge supplied to the charge carriers
91
How is a voltmeter connected?
In parallel.
92
What is the resistance of an ideal voltmeter?
Infinite.
93
What is thermionic emission?
The emission of electrons from the surface of a heated metal.
94
What is the work done on an electron when it passes through a p.d. of V volts?
eV where e is the charge on the electron.
95
What is Ohm's Law?
For a metallic conductor at constant temperature the p.d. is proportional to current.
96
What is electrical resistance?
The opposition of an object to a flow of current through it.
97
How is resistance calculated?
V/I
98
What units are equivalent to an Ohm?
VA⁻¹
99
Why does resistance increases with temperature?
The amplitude of lattice ion vibrations increases causing more frequent collisions between electrons and lattice ions, leading to the electrons doing more work as they move through the wire.
100
Why does current flow lead to heating in components?
Electrons collide with the lattice ions and transfer some of their kinetic energy to the lattice ion's vibrations.
101
What is an Ohmic conductor?
An object for which p.d. is proportional to current.
102
What is meant by the threshold pd of a diode?
The pd at which resistance starts to fall rapidly as pd increases.
103
What are the units of resistivity?
Ωm
104
What is ρ in R = ρL / A?
The resitivity of the material.
105
What is L in R = ρL / A?
The length of the wire.
106
What is A in R = ρL / A?
The cross-sectional area of the wire
107
As a metal gets hotter what happens to its resitivity?
It increases.
108
What is meant by a negative temperature coefficient component?
One in which the resistance drops as temperature increases.
109
Why does resistance of a thermistor fall as temperature increases?
The number density of charge carriers increases.
110
What are thermistors commonly used in?
Temperature sensors.
111
Why does the resistance of an LDR as light intensity changes?
Light increases the number density of charge carriers in the LDR.
112
What are LDRs commonly used in?
Light intensity sensors.
113
What happens to the resistance of an LDR as light intensity increases?
It decreases.
114
What is a kilowatt-hour (kWh)?
The energy supplied when 1kW of power is supplied for 1 hour.
115
How many Joules are equavlent to a kWh
3.6MJ
116
State Kirchoff's second law.
Sum of the EMFs is equal to the sum of the potential drops around a closed circuit loop.
117
What law is Kirchoff's second law a consequence of?
Conservation of Energy
118
What can we say about the current through components in series?
Same for each component
119
What can we say about the current on different parallel branches?
It depends on the resistance of each branch.
120
What can we say about the pd across parallel branches in a circuit?
It is the same for each branch
121
How do find the total pd across several components in series?
It is equal to the sum of the pds across each component
122
How do you find the total EMF from cells connected in series with the same polarity?
Their EMFs are added
123
How do you find the total EMF from cells connected in series with opposite polarity?
The total EMF is the difference between their EMFs
124
How do you calculate the total resistance of resistors in series?
Sum of the individual resistances
125
What is the total resistance of n identical resistors in series?
n x R
126
What is the total resistance of n identical resistors in parallel?
R ÷ n
127
How do you calculate the resistance of resistors in parallel?
1/RT=1/R1+1/R2...
128
How does the total resistance change when a resistor is added in series?
It always increases
129
How does the total resistance change when a resistor is added in parallel?
It always decreases
130
What is the effect of connecting two identical resistors in parallel?
Resistance is halved
131
What is the effect of connecting two identical resistors in series?
Resistance is doubled
132
What is internal resistance?
The opposition to current created by the charge carriers having to flow through the source of EMF
133
What are the lost volts for a power supply?
The pd dropped across the internal resistance OR the difference between the EMF and the terminal pd.
134
What happens to the terminal pd of a source as the current supplied increases?
It falls due to the increasing lost volts to the internal resistance.
135
How do you calculate lost volts for a supply?
Ir where r is the internal resistance.
136
What is the relationship between EMF, terminal pd and lost volts?
EMF = terminal pd + lost volts
137
How do you find the internal resistance from a graph or terminal pd against current?
-gradient
138
How do you find the EMF from a graph or terminal pd against current?
y-intercept
139
What is a potential divider?
Two or resitances in series with a fixed source of EMF.
140
What determines the ratio of the pd across the resistors in a potential divider?
It is equal to the ratio of their resistances.
141
How can a light sensor be made?
By creating a potential divider containing an LDR.
142
How can a temperature sensor be made?
By creating a potential divider containing a thermistor.
143
What component can be used to supply an adjustable output pd?
A potentiometer.
144
What is a progressive wave?
A progressive wave that transfers energy through space.
145
What is a transverse wave?
A wave in which the oscillations are perpendicular to the direction of wave propagation
146
What is a longitudinal wave?
A wave in which the oscillations are parallel to the direction of wave propagation
147
Give an example of a longitudinal wave
Sound, primary seismic waves
148
Give an example of a transverse waves
Waves on a stretched string, secondary seismic waves, electromagnetic radiation
149
What are the regions of high pressure in a longitudinal wave called?
Compressions
150
What are the regions of low pressure in a longitudinal wave called?
Rarefactions
151
What is the displacement of a wave?
The distance of a particle in the medium from it's equilibrium position in a particular direction.
152
What is the equilibrium position in wave motion?
The position of the medium when undisturbed by a wave.
153
What is the amplitude of a wave?
Maximum displacement of the medium from the equilibrium position.
154
What is the frequency of a wave?
The number of wave cycles per second OR the number of waves passing a point per unit time
155
What is the time period of a wave?
Time taken for one complete oscillation OR time for a whole wavelength to pass a fixed point.
156
What is the relationship between frequency and time period?
f = 1/T or inverse proportionality
157
How many radians of phase are there in one complete wave cycle?
2π rad
158
What term describes a phase difference of zero between two points on a wave?
In phase
159
What term describes a phase difference of pi radians between two points on a wave?
In antiphase
160
What is the phase difference between points half a wavelngth apart?
180 degrees OR π rad
161
What is the phase difference between points quarter of a wavelngth apart?
90 degrees OR π/2 rad
162
What is an oscillation?
A displacement one way and then the other about an equilibrium position.
163
What is diffraction?
The spreading out of waves after passing through a slit/around an obstacle.
164
What effect does reducing the size of a single slit have on diffraction?
Diffracted waves spread out more
165
What is the effect of decreasing the wavelength on diffraction?
Diffracted waves spread out less
166
What is meant by the intensity of a wave?
Intensity is the energy delivered by the wave per second per square metre normal to the wave
167
How is the intensity of a wave related to the amplitude?
Intensity is proportional to amplitude squared.
168
How does intensity vary with distance from a point source of waves?
Inverse square law or I = P / 4πr²
169
What is a mechanical wave
A wave that requires a medium.
170
What is the difference between mechanical waves and electromagentic waves?
EM waves don't require a medium.
171
What is an electromagneitc wave?
An oscillation of the electric and magentic fields at right angles to each other.
172
What is the speed of all EM waves in a vacuum/air?
3x10⁸ms⁻¹
173
List the regions of the EM spectrum in order of incresasing wavelength.
Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma rays
174
Which two regions of the EM spectrum overlap?
X-rays and gamma rays.
175
State the range of wavelengths (in powers of 10) of radio waves
>10⁻¹
176
State the range of wavelengths (in powers of 10) of microwaves
10⁻¹ - 10⁻³
177
State the range of wavelengths (in powers of 10) of infrared
10⁻³ - 10⁻⁶
178
State the range of wavelengths of visible light
7x10⁻⁷ - 4x10⁻⁷
179
State the range of wavelengths (in powers of 10) of ultraviolet
10⁻⁷ - 10⁻⁸
180
State the range of wavelengths (in powers of 10) of Xrays
10⁻⁸ - 10⁻¹³
181
State the range of wavelengths (in powers of 10) of gamma rays
<10⁻¹⁰
182
Why can't longitudinal waves be polarised?
Longitudinal waves already only have a single driection of oscillation.
183
What is the effect of a polarising filter?
It only transmits the component of the oscillations parallel to the filter
184
What is the effect of perpendicular polarising filters
No light is transmitted
185
Give a use of polarising filters.
LCD screens, 3D TV, polarimetry in manufacturing, anti-glare sunglasses
186
What effect does reflection have on the polarisation of light?
Reflected light is partially polarised in the plane of the surface.
187
What effect does scattering light have on polarisation?
Scattered light is polarised
188
Which wave property always remains constant when a wave travels from one medium to another?
Frequency
189
When entering a material with a higher refractive index what happens to wave speed?
decreases
190
When entering a material with a lower refractive index what happens to wavelength?
increases
191
What is the definition of the refractive index of a material
Speed of light in a vacuum/Speed of light in material
192
What are the angles of incidence and refraction measured relative to?
The normal to the boundary
193
Which way do waves refract when entering a material with a higher refractive index?
Toward the normal
194
Which way do waves refract when entering a material with a lower refractive index?
Away from the normal
195
What is the angle of refraction at the critical angle?
Ninety degrees
196
What are the conditions required for total internal reflection?
Wave must be travelling in a material with a higher index and meeting a boundary with a material of lower refractive index.The angle of incidence must be greater than the critical angle.
197
What two phenomena occur when a wave goes from a higher to a lower refractive index at an angle of incidence less than the critical angle?
The ray is refracted and partially reflected.
198
What is the principle of superposition
When two waves meet at a point the resultant displacement is the (vector) sum of the displacements of the individual waves.
199
What is constructive interference?
When two waves superpose in phase causing an increase amplitude.
200
What is destructive interference?
When two waves superpose in antiphase causing a decreased amplitude.
201
What are coherent sources of waves?
Sources that emit waves with a constant phase difference (and the same frequency).
202
What is an interference pattern?
A pattern of regions of constructive and destructive interference produced by coherent sources of waves.
203
What path difference is required for waves to be in phase?
A whole number of wavelengths
204
What path difference is required for waves to be in antiphase?
An odd number of half wavelengths
205
What is the relationship between path difference and phase difference for coherent sources?
(Path difference/wavelength) x 2π
206
What term describes a phase difference of zero between two waves?
In phase
207
What term describes a phase difference of π radians between two waves?
In antiphase
208
What is x in the double slit equation (λ = ax/D)?
Fringe seperation
209
What is D in the double slit equation (λ = ax/D)?
Distance between the double slits and the screen
210
What is a in the double slit equation (λ = ax/D)?
Distance between the double slits
211
What occurs to cause a dark fringe in the double slit experiment?
Destructive interference of the light from each slit
212
What occurs to cause a bright fringe in the double slit experiment?
Constructive interference of the light from each slit
213
What did Young's double slit experiment demonstrate about the nature of light?
That light exhibits wave behaviour.
214
What name is given to light of a single frequency/wavelength?
Monochromatic
215
Why did Young place a single slit before the double slit?
To ensure the light from each of the double slits was in phase.
216
What are the condition required for a stationary wave to form?
Two waves travelling/propagating in opposite directions superpose with the same frequency and similar amplitudes
217
What is an antinode on a stationary wave?
A point where the progressive waves are in phase and constructively interfering resulting in maximum amplitude
218
What is an node on a stationary wave?
A point where the progressive waves are in antiphase and are destructively interfering resulting in minimum amplitude
219
How many wavelengths are there between adjacent nodes of a standing wave?
Half a wavelength
220
What is the phase difference between points either side of a node in a standing wave?
Pi Rad/180 degrees
221
What is the phase difference of points that are between two adjacent nodes of a standing wave?
Zero
222
How does phase vary along a progressive wave?
Changes continuously across each wave cycle.
223
How does amplitude vary in a stationary wave?
It varies continuously along the wave. It is a maximum at antinodes and a minimum at nodes.
224
How does amplitude vary in a progressive wave?
It is the same at every point along the wave.
225
What type of wave doesn't tranfer energy?
Stationary waves
226
What is the fundamental frequency of a string?
The lowest frequency which produces a stationary wave on the string.
227
What factors determine the fundamental frequency on a string
Length, tension and the thickness of the string.
228
What determines the pitch produced by a stationary wave in a musical instrument?
The frequency of the 1st harmonic
229
What determines the loudness of sound?
The amplitude of the sound wave
230
Why can only certain frequency stationary waves be produced on a stretched string?
There must be nodes at the fixed ends and only certain frequencies/wavelengths allow this.
231
What feature of a stationary wave is always formed at an open end of a tube?
(Displacement) Antinode
232
What feature of a stationary wave is always formed at a closed end of a tube?
(Displacement) Node
233
What determines the energy of a photon?
The frequency/wavelength
234
What is a photon?
A quantum of energy of electromagnetic radiation
235
How do you calculate the energy of a photon?
E = hf OR E =hc/λ
236
What is an electron volt?
The energy gained or lost by an electron passing through a potential difference of 1V
237
How do convert from eV to J?
multiply by 1.6x10^-19
238
How do convert from J to eV?
divide by 1.6x10^-19
239
What is the threshold p.d. of an LED?
The minimum potential difference required for the LED to produce light.
240
How can the threshold p.d. of an LED be used to find photon energy?
The energy transferred by the electrons (e x V) is equal to the energy of the photons produced (hf).
241
What is meant by wave particle duality?
It describes how all matter can display both wave and particle properties.
242
What is the key piece of evidence for wave particle duality?
When an electron beam passes through polycrystaline graphite it produces a diffraction and interference pattern pattern.
243
What does the De Broglie wave equation apply to?
Everything
244
What is the relationship between momentum and wavelength?
Inverse proportionality
245
What is the photoelectric effect?
The emission of electrons from a metal surface when illuminated with light.
246
What is the atomic structure of a metal?
A lattice of positive ions surrounded by a sea of free electrons.
247
What is a photoelectron?
An electron that has been removed from a metal by absorbing a photon
248
What is the work function?
The minimum energy required to remove an electron from the surface of a metal
249
What is the threshold frequency?
The minimum frequency of light required to produce photoelectrons from a metal
250
What is monochromatic light
Light of a single frequency/wavelength
251
What is the relationship between work function and threshold frequency?
∅ = hf₀
252
What is required for a photon to be able to produce photoelectrons?
Its frequency is greater than the threshold frequency
253
Why can't light sources below the threshold frequency produce photoelectrons?
The photon energy is less than the work function
254
How do photons and electrons interact?
A single photon can be absorbed/emitted by a single electron which gains/loses the energy of the photon.
255
What is the effect on an electron of absorbing a photon?
The electron gains the energy of the photon
256
What effect does increasing the frequency of a monochromatic light source have on photoelectrons produced?
Photoelectrons will have a greater maximum kinetic energy
257
What is the effect of increasing the intensity of a monochromatic light source on photoelectrons produced?
More photoelectrons will be produced but they will have the same maximum kinetic energy
258
Why does the kinetic energy of photoelectrons from monochromatic light vary in the photoelectric effect?
The work function is a minimum energy. Some electrons are liberated from deeper into the metal and require more energy to be liberated.
259
What two factors that determine the maximum kinetic energy of photoelectrons?
The frequency of the light and the work function of the metal
260
What determines the rate at which energy is delivered by a wave?
Intensity/amplitude of the wave
261
What is hf in Einstein's photoelectric effect equation (hf = 𝜙 + KE(max))
The energy of the incident photon.
262
What is 𝜙 in Einstein's photoelectric effect equation (hf = 𝜙 + KE(max))
The work function of the metal.
263
What is KE(max) in Einstein's photoelectric effect equation (hf = 𝜙 + KE(max))
The maximum kinetic energy of the photoelectrons
264
According to the wave model how is energy transferred from light to electrons in a metal?
It is delivered continuously and builds up over time
265
If light is above the threshold frequency, how long will it take for photoelectrons to start being produced?
It is instantaneous
266
What happens if very intense light that is below the threshold frequency is used?
No photoelectrons are produced, regardless of intensity.
267
Describe the construction of a capacitor.
Two conducting plates seperated by an insulator.
268
What is the relationship between charge stored and pd across a capacitor?
Charge is proportional to voltage
269
Describe what happens to the two plates of an uncharged capacitor when a p.d. is applied to it?
Electrons/charge flows off of one plate and flows on to the other causing one to become positive and the other negative.
270
What units are equanivalent to a Farad?
CV-1 or coulombs per volt
271
How do you calauclte the total capacitance for capacitors in parallel?
CT = C1 + C2 + C3 + ....
272
How do you calculte the total capacitance for capacitors in series?
1/CT = 1/C1 + 1/C2 + 1/C3....
273
If capcitors are connected in series what quantitiy is the same for all capacitors?
Charge stored
274
If capcitors are connected in parallel what quantitiy is the same for all capacitors?
p.d.
275
What is representd by the area under a p.d. - charge graphs?
Electrical energy transferred OR work done.
276
What is represented by the gradient of a charge-p.d. graph for a capacitor?
Capacitance
277
What is the relationship between energy stored and p.d. on a capcitor?
Energy stored is proportional to p.d. squared
278
What is the relationship between energy stored and charge on a capcitor?
Energy stored is proportional to charge squared
279
Out of Q, V and I which variable(s) follow the relationship x = x0 e-(t/RC) when discharging a capacitor?
Q, V and I
280
Out of Q, V and I which variable(s) follow the relationship x = x0 e-(t/RC) when charging a capacitor?
I
281
Out of Q, V and I which variable(s) follow the relationship x = x0 (1 - e-(t/RC) ) when charging a capacitor?
Q and V
282
How do you calculate time constant in a capcitor circuit?
RC
283
What is meant by the constant-ratio nature of exponential decay?
In equal time intervals the quantity decreases by equal factors
284
How much charge remains after one time constant when discharging a capacitor?
e-1 OR 0.37 OR 37%
285
How much charge remains after n time constants when discharging a capacitor?
e-n
286
What is represented by the gradient of charge-time graph when charging a capacitor?
Charging current.
287
State a two uses of capacitors.
Energy storage e.g. for camera flashes, spot welding..., timing circuits, voltage smoothing, audio filters.
288
What is an electric field?
A region of space where a charge will experience an electrostatic force.
289
What is the definition of electric field strength?
The force per unit charge on a positive test charge placed at that point
290
What are the units of electric field strength?
NC⁻¹ (or Vm⁻¹)
291
What does ε0 represent?
permittivity of free space
292
What does εr represent?
Relative permittivity (of a dielectric).
293
What does the direction of an electric field line show?
The direction of the force exerted on a positive test charge.
294
What does the spacing of electric field lines show?
Field strength.
295
Are test charges positive or negative?
positive
296
What units equivalent to Vm⁻¹
N C⁻¹
297
When is the equation E = V/d used?
To find the uniform field strength between two parallel plates.
298
What is a dipole?
A pair of opposite sign charges separated by a small distance (e.g. a polar molecule like HCl)
299
State Coulomb's law in words.
The force between two point charges is proportional to the product of the two charges and inversely proportional to the square of their separation distance.
300
What is electric potential difference?
The work done per unit positive charge in moving between two points
301
What is the definition of absolute electric potential of a point?
The work done per unit positive charge to move from infinity to that point in the field.
302
What is the absolute electric potential an infinite distance from a 1C charge?
0
303
What units are equivalent to a V?
J C⁻¹
304
What is the relationship between the electrostatic force between two point charges and their seperation distance?
It is inversely proportional to the square of separation OR inverse square law
305
What is the relationship between potential and distance from a point charge?
Potential α 1/distance
306
What is a uniform electric field?
A region of space in which the electric field strength is the same at all points
307
What is a radial field?
An electric field generated by a point charge OR a field that obeys the inverse square law.
308
What is a neutral point in an electric field?
A point at which the resultant field strength is zero
309
Is electric field strength a vector or a scalar quantity?
Vector
310
Is electrical potential a vector or scalar quantity?
Scalar
311
State a similarity between electric and gravitational fields.
Both obey inverse square law for field strength (around a point mass/charge). Both have infinite range. Both act between two objects at a distance.
312
State two differences between electric and gravitational fields?
Gravitational fields act on masses, electric fields on charges: electric fields are much stronger that gravitational fields: electric fields can be attractive or repulsive, gravitational fields are always attractive: potential is always negative in a gravitational field.
313
When is the equation V = Q / (4 pi ε0 r) used?
To find the potential around a point charge/in a radial field.
314
When is the equation C = 4 x pi x ε0 x R used?
To calculate the capacitance on an isolated sphere.
315
What is represented by R in the equation C = 4 x pi x ε0 x R used?
The radius of an isolated sphere.
316
What is the relationship between electric potential energy and electric potential?
EPE = V x q where q is the charge in the field.
317
What creates a magnetic field?
Moving charges and permanent magnets.
318
What is shown by the direction of a magnetic field line?
The direction of force on a free north pole.
319
Which direction do magnetic field lines flow in?
From north to south.
320
How is a uniform magnetic field represented by field lines?
Parallel
321
What does the spacing of magnetic field lines show?
Magnetic field strength/flux density.
322
How do you find the direction of the field lines around a current?
Using the right hand grip rule.
323
How is a field line or current running into the paper shown?
⊗
324
How is a field line or current running out of the paper shown?
. in a circle
325
Why does a current experience a force in a magnetic field?
The current's magnetic field interacts with the external one.
326
What is represented by the thumb in Fleming's Left Hand rule.
(Direction of) force
327
What is represented by the first finger in Fleming's Left Hand rule.
(Direction of the) magnetic field
328
What is represented by the second finger in Fleming's LHR?
(Direction of) current
329
When is Fleming's Left Hand Rule used?
To find the direction of a current/moving charge in a magnetic field.
330
When is the equation F = BIL sinθ used?
To find the magnitude of force on a wire (carrying current) in a magnetic field.
331
What is represented by θ in the equation F = BIL sinθ?
The angle between the current and the field direction.
332
What is the SI unit of flux density?
Tesla (T)
333
How is a magnetic flux density defined?
The field strength that would cause a wire carrying a current of 1A perpendicular to the field to experience a force of 1N per m of length.
334
What experiment can be done to find flux density in the lab?
Set up a current carrying wire between the poles of a magnet on top of a toppan balance.
335
When is the equation F = Bqv used?
To find the force acting on a particle moving (at right angles) to a magnetic field?
336
When is the equation r = mv/BQ used?
To find the radius of the path of a particle moving in a uniform magnetic field.
337
Why does a charged particle describe circular motion in a uniform magnetic field?
(There is a constant) force always acting at right angles to motion.
338
Why do only particles with the correct velocity travel in a straight line in a velocity selector?
The electric force balance the magnetic force (at this velocity).
339
How is magnetic flux defined?
It is the total component of the magnetic flux density passing at right angles through a surface of area A OR ∅ = BA cosθ
340
What are the SI units of flux?
Wb (Weber)
341
What is represented by ∅ in the equations ∅ = BA cosθ?
Flux
342
What is the relationship between flux and flux linkage?
Flux lingage is flux multiplied by the number of turns on the coil
343
What is represented by θ in the equations ∅ = BA cosθ?
The angle between the flux/field and the normal/perpendicular to the surface.
344
How is flux linkage caluclated?
N∅ where N is the number of turns on the coil and ∅ is the flux passing theorugh the coil.
345
What is the relationship between flux and flux density?
Flux density is the flux per unit area perpendicular to the field.
346
How is flux represented in a field line diagram?
The total number of field lines passing through the object/surface.
347
How is flux density represented in a field line diargram?
The spacing of field lines.
348
What other units are Tesla commonly expressed in?
Wbm⁻² (or Nm⁻¹A⁻¹)
349
State Faraday's law.
The magnitude of an induced EMF is directly proportional to the rate of change of flux linkage.
350
What is represented by ε in the equation ε = -∆(N∅)/∆t?
Induced EMF.
351
What is law is represented by the proportionalilty ε α ∆(N∅)/∆t?
Faraday's Law (of electromagnetic induction).
352
State Lenz's law.
The direction of an induced EMF or current is always in such a direction as to oppose the change that created it.
353
What principle leads to Lenz's law?
Conservation of energy.
354
Why is there a negative sign in the equation ε = -∆(N∅)/∆t?
It is due to Lenz's law OR conservation of energy.
355
What type of trnaformer has more turns on its primary coil?
A step down transformer.
356
What type of trnaformer has more turns on its secondary coil?
A step down transformer.
357
State two ways in which energy losses are transformeres reduced?
Low resistance primary and secondary windings/laminated core/soft iron core
358
Why is a lamintaed core used in a transformer?
To reduce the heating effect of (induced) eddy currents.
359
What is a laminated core?
A core made up of layers that are seperated by an insulator.
360
What is meant by soft iron?
Iron that can be easily magentised and demagnetised.
361
What is an eddy current in a tranformer?
A current induced by the changing flux in the core.
362
What material was used as a target in Rutherford's scattering experiment?
Gold foil, a few atoms thick
363
What was measured in Rutherford's scattering experiment?
The angle of deflection of the alpha particles.
364
What happened to most of the alpha particle in Rutherford's scattering experiment?
They passed straight through the foil (with very little scattering).
365
What proportion of alpha particles were scattered in Rutherford's scattering experiment?
Around 1 in 2000
366
What proportion of alpha particles were deflected by more than 90° in Rutherford's scattering experiment?
Around 1 in 10,000
367
What was concluded due to most of the alpha particles passing straight through the gold foil Rutherford's scattering experiment?
Most of the atom is empty space with most of the mass concentrated in a small nucleus.
368
What was concluded due to some alpha particles being scattered in Rutherford's scattering experiment?
The nucleus is positively charged.
369
How did Rutherford estimate the maximum radius of the nucleus?
He equated the KE of the alpha particle to the electric potential energy at closest approach to the nucleus.
370
What is a nucleon?
A proton or neutron.
371
What is an isotope?
A nucleus of an element with the same number of protons but a different number of neutrons.
372
What is an atomic mass unit?
One twelfth of the mass of a neutral carbon 12 atom.
373
How has the radius of the nucleus been measured?
By the diffraction of fast moving electron.
374
What is R in R = r₀A^(1/3)?
The radius of the nucleus.
375
What is r₀ in R = r₀A^(1/3) roughly equivalent to?
The radius of a proton.
376
What is A in R = r₀A^(1/3)
Nucleon number.
377
What force holds protons and neutrons together in the nucleus?
The strong nuclear force.
378
What is the maximum range of the strong nuclear force?
~3fm
379
Below what distance is the strong nuclear force repulsive?
0.5fm
380
Which group of particles are subject to the weak nuclear force but not the strong nuclear force?
Leptons
381
What is the quark composition of a meson?
A quark and an antiquark.
382
Which force do Hadrons decay by?
The weak nuclear force.
383
What is the quark composition of a Baryon?
Three quarks
384
What is a neutrino?
A lepton with no charge and a tiny mass.
385
Why doesn't a neutrino experience the electromagnetic force?
They have no charge.
386
What is the quark composition of a neutron?
up down down (udd)
387
What is the quark composition of a proton?
up up down (uud)
388
What is the quark composition of an anti-baryon?
Three antiquarks
389
Name the two types of hadron.
baryons and mesons
390
What force hold quarks together in hadrons?
The strong nuclear force.
391
What is the family of particles that are subject to both the strong and weak nuclear force?
Hadrons
392
What type of particle are nucleons?
Baryons
393
How does a proton compare to an antiproton?
The have the same mass but opposite charge.
394
How does an electron compare to a positron?
The have the same mass but opposite charge.
395
What is the antiparticle of the electron?
Positron.
396
What type of particle are there millions of passing through your body every second?
Neutrinos
397
Describe beta minus decay.
A neutron in an unstable nucleus decays into a proton and emits an electron and an antineutrino.
398
Describe beta plus decay.
A proton in an unstable nucleus decays into a neutron and emits a positron and a neutrino
399
What quark transformation occurs during beta minus decay?
A down quark (in a neutron) turns into an up quark (in a proton)
400
What quark transformation occurs during beta plus decay?
An up quark (in a proton) turns into an down quark (in a neutron)
401
What is meant by ionising radiation?
Radiation with sufficient energy to ionise atoms by removing electrons.
402
What is the charge of gamma radiation?
0
403
What is a Beta minus particle?
A fast moving electron (emitted from a nucleus)
404
What is a Beta plus particle?
A fast moving positron (emitted from a nucleus)
405
What is an alpha particle?
2 protons and 2 neutrons OR a helium nucleus
406
What is the speed of gamma radiation?
3x10⁸ms⁻¹
407
What type of nuclear radiation has the greatest rest mass?
Alpha radiation
408
What is gamma radiation?
A high energy photon (emitted by the nucleus)
409
What is the charge of an Alpha particle?
+3.2x10⁻¹⁹C OR +2e
410
What is the charge of a beta minus particle?
-1.6x10⁻¹⁹C OR -e
411
What type of nuclear radiation is not deflected by electric and magnetic fields?
Gamma rays
412
What type of nuclear radiation is deflected the most by electric and magnetic fields?
Beta radiation
413
When measuring the count rate of a radioactive source what must be taken into account?
The background count rate / count rate with no source present
414
How do you find the corrected count rate for a radioactive source from the measured count rate?
Measured count rate - background count rate
415
How far do alpha particles typically travel in air?
A few cm
416
What type of ionising radiation is stopped by a sheet of paper?
Alpha radiation
417
Why are alpha particles strongly ionising?
They have a relatively large mass and charge.
418
What is the range of beta particles in air?
Around 1m
419
What type of radiation requires around 1-3mm of aluminium to stop it?
Beta radiation
420
What type of radiation is the least ionising?
Gamma rays
421
Why is gamma the least ionising form of radiation?
It has no charge.
422
What thickness of lead will stop a significant proportion of gamma rays?
3-4cm
423
Why is ionising radiation dangerous?
It can damage living cells and DNA.
424
What procedure is routinely used to minimise the dose when handling radioactive sources in the lab?
Use tongs and hold it away from your body.
425
What are the three key steps for reducing radiation dose?
Maximise distance from source, minimise exposure time and use shielding.
426
What provides the energy of the X-rays in an X-ray tube?
The kinetic energy of the accelerated electrons.
427
What is an X-ray?
A photon produced by the deceleration of a fast moving electron
428
What is the typical p.d. of an X-ray tube for medical imaging?
30-100kV
429
What causes the emission of electrons from the cathode in an X-ray tube?
It is heated to produce thermionic emission.
430
What name is given to the anode in an X-ray tube?
The target metal.
431
What is an essential property for the target metal in an X-ray tube?
High melting point.
432
What causes the production of X-rays in an X-ray tube?
The deceleration of electrons when they hit the target metal/anode.
433
In an X-ray tube what happens to most of the kinetic energy lost by the electrons when they hit the anode?
It is transferred to thermal energy of the anode.
434
What measures can be taken to prevent an anode melting in an X-ray tube?
It is cooled by oil or rotated.
435
What feature of X-ray tubes protects the radiographer?
Lead lining.
436
What determines the maximum frequency of X-rays produced in an X-ray tube?
The maximum kinetic energy of a single electron.
437
When is the equation λ = hc/eV used?
To find the minimum wavelength of X-rays produced (by an X-ray tube).
438
What is V in the equation λ = hc/eV?
The accelerating potential difference.
439
Describe the beam used by CAT scanners.
A thin (1-10mm) fan.
440
What happens to the position of the X-ray tube during a CAT scan?
It rotates around the patient.
441
What are the key advantages of CAT scans over conventional X-rays?
They produce a 3D image and can distinguish between tissues with similar attenuation coefficients.
442
What are the disadvantages of CAT scans compared to conventional X-rays?
The radiation dose is greater, they are more expensive, and take more time.
443
How does a CAT scan produce a 3D image?
A series of slices are imaged and processed via a computer.
444
What is X-ray attenuation?
The decrease in intensity as X-rays pass through matter.
445
What are the four mechanisms of X-ray attenuation?
Simple scatter, Photoelectric Effect, Compton Scattering, Pair Production.
446
What occurs during simple scatter of X-rays?
The X-ray interacts with an electron in an atom and changes direction but not energy.
447
Which method of attenuation is most significant with X-rays with energy in the range 1-20keV?
Simple scatter.
448
What occurs during the photoelectric effect attenuation of X-rays?
The X-ray is absorbed by an electron in an atom which gains the energy of the photon and leaves the atom.
449
Which method of attenuation is significant with X-rays with energies up to 100keV?
Photoelectric effect.
450
Which method of attenuation is most significant to medical X-ray imaging?
The photoelectric effect.
451
What occurs during Compton scattering attenuation of X-rays?
The X-ray interacts with an electron in the atom causing the electron to be ejected and the photon to be scattered with reduced energy.
452
Which method of attenuation is significant with X-rays with energy in the range 0.5-5MeV?
Compton scattering.
453
What occurs during pair production with X-rays?
An X-ray interacts with the nucleus of an atom converting the energy of the photon to an electron and a positron.
454
Which method of attenuation occurs with X-rays with energies 1.02MeV?
Pair production.
455
What is I in the equation I = I₀e^(-µx)?
Transmitted intensity.
456
What is I₀ in the equation I = I₀e^(-µx)?
Intensity before absorption.
457
What is µ in the equation I = I₀e^(-µx)?
Attenuation/absorption coefficient.
458
What is x in the equation I = I₀e^(-µx)?
Thickness of the absorbing substance.
459
What are the SI units of attenuation coefficient?
m⁻¹.
460
What is a contrast medium in X-rays?
A material with a high attenuation coefficient used to image soft tissue.
461
What contrast medium is typically used to examine blood flow?
Iodine.
462
What contrast medium is typically used to image the digestive system?
Barium sulfate.
463
How are X-rays used for cancer therapy?
A linear accelerator produces high-energy X-rays that destroy cells.
464
Why are high-energy X-rays preferable to gamma radiation for cancer therapy?
An X-ray source can be turned off.
465
Which radionuclide is used for imaging with a gamma camera?
Technetium-99m.
466
Which radionuclide is used in PET scanning?
Fluorine-18.
467
Why are gamma-emitting sources useful for imaging inside the body?
They are the least ionising and can penetrate through a patient to be detected externally.
468
Why are short half-lives necessary for the radioisotopes used for medical imaging?
To ensure a large activity from a small amount and to minimise radiation dose after the procedure.
469
What is a medical tracer?
A compound containing a radioisotope that is put into the patient's body.
470
What is the function of a collimator in a gamma camera?
To absorb any photons not travelling along the axis of the tubes so the source location of gamma radiation can be identified.
471
How is a collimator in a gamma camera constructed?
It is a honeycomb of long, thin lead tubes.
472
What is the function of a scintillator in a gamma camera?
It produces many photons of visible light when a gamma photon interacts with it.
473
What is the function of the photomultiplier tubes in a gamma camera?
They convert visible light photons to an electrical pulse.
474
What is the function of the computer in a gamma camera?
It processes the signals from the photomultipliers to locate where the gamma ray originated to produce an image showing the concentrations of medical tracer.
475
What type of radiation is detected in a PET scan?
Gamma.
476
What type of radiation is emitted by Fluorine-18 nucleus in a PET scan?
Beta plus / positron.
477
What process produces gamma photons in a PET scan?
Electron and positron annihilation.
478
How is the source of the gamma photons located in a PET scan?
By the time delay between the arrival of diametrically opposite gamma photons.
479
What is the typical time delay between the arrival of gamma photons in PET scan?
Nanoseconds.
480
Why is medical imaging using gamma emitting tracers useful?
It can measure the function of organs in the body rather than just the structure.
481
What are the disadvantages of a PET scan?
They are expensive and require facilities to prepare tracers local to the scanner.
482
What is the range of human hearing?
20 Hz - 20 kHz.
483
What is an ultrasound transducer?
A device for emitting and detecting ultrasound.
484
What is the minimum frequency of ultrasound?
20 kHz.
485
What is the piezoelectric effect?
When a crystal produces an EMF when it is distorted.
486
What happens to a piezoelectric crystal when p.d. is applied across opposite faces?
It is compressed or stretched.
487
What are the main advantages of ultrasound imaging?
It is non-invasive and does not require ionising radiation.
488
What range of frequencies are typically used for ultrasound scans?
1 - 15 MHz.
489
How is an ultrasound pulse generated by a transducer?
A high frequency p.d. is applied at the natural frequency of the piezoelectric crystal causing the crystal to resonate.
490
How is an ultrasound pulse detected by a transducer?
Sound incident on the crystal causes it to vibrate generating an EMF across its faces.
491
What is the purpose of the damping material in an ultrasound scanner?
It prevents reflection of the pulse from behind the piezoelectric crystal.
492
What is an ultrasound A-scan?
A single transducer produces pulses that travel along a single path through the patient.
493
How does an ultrasound A-scan calculate the distance to boundaries between tissues?
2 x Distance = v x t, where v is the speed of the ultrasound and t is the time interval between the emitted and reflected pulse.
494
What is an ultrasound B-scan?
The signal from an array of transducers is processed by computer to build up a 2D image.
495
What determines the brightness of the dots on a B-scan display?
The amplitude of the reflected ultrasound from that point.
496
What determines the acoustic impedance of a substance?
The density and the speed of sound in the substance.
497
What are the units of acoustic impedance?
kg m⁻² s⁻¹
498
What is the intensity reflection coefficient for ultrasound?
The ratio (reflected intensity of ultrasound ÷ incident intensity of ultrasound)
499
What factor determines the reflection intensity coefficient for ultrasound at a boundary?
The difference between the acoustic impedances of the two substances.
500
Why does a coupling gel need to be used when performing an ultrasound?
Air pockets between the transducer and skin cause reflection of nearly all of the ultrasound at the skin-air boundary.
501
What is an ultrasound coupling gel?
A substance applied to the skin and transducer with an impedance similar to skin.
502
What is impedance/acoustic matching?
When two substances have similar acoustic impedances so negligible reflection of ultrasound occurs.
503
What causes ultrasound to undergo Doppler shift?
Reflection from moving blood cells.
504
What is Doppler ultrasound used for?
Measuring the speed (and volume) of blood flow.
505
What is measured in Doppler ultrasound to determine the velocity of the blood?
The observed change in frequency of the reflected ultrasound pulse.
506
How is blood flow viewed during a Doppler ultrasound?
The signal is processed by computer and displayed as a colour-coded image on a screen.
507
Why does the transducer have to be placed away from the normal during a Doppler ultrasound?
To ensure there is a component of the blood flow's velocity in the direction of the ultrasound pulse.
508
What is ∆f in the equation ∆f = (2fvcosθ)/c?
Change in the observed frequency of the reflected ultrasound.
509
What is v in the equation ∆f = (2fvcosθ)/c?
Blood flow speed.
510
What is θ in the equation ∆f = (2fvcosθ)/c?
The angle between the transducer axis and the blood flow.
511
What is c in the equation ∆f = (2fvcosθ)/c?
The speed of ultrasound in blood.
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