head start Flashcards
(157 cards)
1
Q
what is standard scientific notation?
A
using conventional symbols and units, and writing very large and very small numbers in standard form
2
Q
what is index notation?
A
writing units like m/s as ms^-1
3
Q
what does ms^-1 mean?
A
m/s
4
Q
what is the standard symbol and unit for displacement?
A
symbol: s
unit: metre, m
5
Q
what is the standard symbol and unit for time?
A
symbol: t
unit: second, s
6
Q
what is the standard symbol and unit for velocity?
A
symbol: v
unit: metre per second, ms^-1
7
Q
what is the standard symbol and unit for acceleration?
A
symbol: a
unit: metre per second squared, ms^-2
8
Q
what is the symbol for metres per second squared?
A
ms^-2
9
Q
what is the standard symbol and unit for mass?
A
symbol: m
unit: kilogram, kg
10
Q
what is the standard symbol and unit for force?
A
symbol: F
unit: newton, N
11
Q
what is the standard symbol and unit for gravitational field strength?
A
symbol: g
unit: newton per kilogram, N kg^-1
12
Q
what is the standard symbol and unit for energy?
A
symbol: E
unit: joule, J
13
Q
what is the standard symbol and unit for work?
A
symbol: W
unit: joule, J
14
Q
what is the standard symbol and unit for power?
A
symbol: P
unit: watt, W
15
Q
what is the standard symbol and unit for frequency?
A
symbol: f
unit: hertz, Hz
16
Q
what is the standard symbol and unit for wavelength?
A
symbol: λ
unit: metre, m
17
Q
what is the standard symbol and unit for charge?
A
symbol: Q
unit: coulomb, C
18
Q
what is the standard symbol and unit for electric current?
A
symbol: I
unit: ampere, A
19
Q
what is the standard symbol and unit for potential difference?
A
symbol: V
unit: volt, V
20
Q
what is the standard symbol and unit for resistance?
A
symbol: R
unit: ohm, Ω
21
Q
what does the prefix “tera” (T) mean?
A
a multiple of 10^12
22
Q
what does the prefix giga (G) mean?
A
a multiple of 10^9
23
Q
what does a prefix of mega (M) mean?
A
a multiple of 10^6
24
Q
what does a prefix of kilo (k) mean?
A
10^3
25
what does a prefix of centi- (c) mean?
a multiple of 10^-2
26
what does a prefix of "milli-" (m) mean?
a multiple of 10^-3
27
what does a prefix of "micro-" (μ) mean?
a multiple of 10^-6
28
what does a prefix of "nano-" (n) mean?
a multiple of 10^-9
29
what does a prefix of "pico-" (p) mean?
a multiple of 10^-12
30
what does a prefix of "femto-" (f) mean?
a multiple of 10^-15
31
what do you do if the question asks you to "give your answer to an appropriate number of significant figures"?
round your answers to the same number of significant figures as the given data value you've used in the calculation with the least significant figures. Then write the number of significant figures you've rounded your answer to
32
give some limitations of the equation speed = distance/time
1. it only tells you the average speed. The object could vary its speed from fast to slow and even go backwards. So long as it gets from A to B in the same time you get the same answer.
2. We assume that the object takes the shortest possible path between the two points (a straight line) rather than meandering around
33
give the equation that connects displacement, velocity and time taken (include units)
velocity (ms^-1) = displacement (m) / time taken (s)
v = s/t
34
what do you need to do whenever you make a scale drawing?
make sure you state the scale you are using
35
can you use an arrow to represent velocity, because it's a vector?
yes - the longer the arrow, the greater the speed of the object. A typical scale might be 1 cm to 1 ms^-1
36
what do you do to add two velocity or displacement distances?
you can't simply add together the two distances as this doesn't account for the different directions of the vectors. What you do is:
1. Draw arrows representing the two vectors
2. Place the arrows one after the other "tip-to-tail".
3. Draw a third arrow from start to finish. This is your resultant vector.
OR use Pythagoras if the vectors make a right angle triangle
37
how do you subtract vectors?
you need to flip the direction of the vector you are subtracting. This changes the sign of the vector. Adding the flipped vector is the same as subtracting the vector (3-4 = 3 + -4). If the vectors are at right angles you can also use Pythagoras.
38
what is resolving vectors?
basically the opposite of finding the resultant - you start from the resultant vector and split it into two separate vectors at right angles to each other.
39
what do you need to do to find the components of a vector, v?
you need to use trigonometry (a resultant vector and its components make a right-angled triangle - you can use cos to find the lengths of the components or the angles)
40
why is it useful to resolve vectors? Give a real life example of this.
because the two components of a vector don't affect each other. This means you can deal with the two directions completely separately:
e.g. if you throw a ball diagonally up and to the right:
- only the vertical component of the velocity is affected by gravity
- you can calculate the ball's vertical velocity (which will be affected by gravity)
- and you can calculate the ball's horizontal velocity (which won't be affected by gravity)
41
what is acceleration? is it a scalar or a vector?
the rate of change of velocity. Like velocity, it is a vector quantity.
42
give two equations for acceleration, include units
1. acceleration (ms^-2) = change in velocity (ms^-1) / time taken (s) ((delta v) / t)
2. acceleration = (final velocity - initial velocity)/time taken (a = (v-u)/t)
43
give an equation for acceleration, include units
acceleration (ms^-2) = change in velocity (ms^-1) / time taken (s)
delta v / t, or (v-u)/t where v is the final velocity and u is the initial velocity.
44
what is deceleration? Which direction does it act in?
negative acceleration and acts in the opposite direction to motion.
45
what do you do when calculating acceleration with velocities in different directions?
you'll often only need to think about velocities in one dimension, say left to right. But you still need to recognise the difference between velocities from right to left and velocities from left to right.
choose a direction to be positive (usually right). All velocities in this direction will from now on be positive, and all those in the opposite direction will be negative
46
what is the acceleration due to gravity, and what is the symbol for it? Is it usually positive or negative?
when an object is dropped, it accelerates downwards at a constant rate of roughly 9.81 ms^-2. This is the acceleration due to gravity and it has the symbol g. It usually seems sensible to take the upward direction as positive and down as negative, making the acceleration due to gravity -9.81 ms^-2
47
what does a displacement-time graph tell you? What does it not tell you?
how far an object is from a given point, in a given direction, as time goes on. As the object moves away from that point the displacement on the graph goes up, and as it moves towards it the displacement goes down. However, these graphs only tell you about the motion in one dimension - e.g. a graph could tell you how far up a ball had been thrown, but not how far it has moved horizontally.
48
what is the gradient of the line in a displacement-time graph?
the velocity - velocity = displacement / time, so the gradient of a displacement-time graph tells you how fast an object is travelling, and what direction it is moving in.
49
what does a straight line in a displacement-time graph mean?
the velocity is constant
50
what does a curved line in a displacement-time graph mean?
the object is accelerating or decelerating (the velocity is changing)
51
on a displacement-time graph, does a steepening curve mean acceleration or deceleration?
acceleration
52
on a displacement-time graph, does a flattening curve mean the object is accelerating or decelerating?
decelerating
53
what can you use a velocity-time graph to calculate?
1. the distance the object has moved
2. The acceleration
54
what is the area under the line in a velocity-time graph? Why?
the distance travelled - the area under the line is usually a trapezium, sowhen you're working out the area, you're multiplying time (the horizontal length) by average speed (the average vertical length) so the result is distance
55
give 2 ways to work out the area under a velocity time graph
1. divide the shape into trapeziums, triangles, and/or rectangles and add up the area of each one
2. Or work out how many metres each grid square on the graph is worth, then multiply by the number of squares under the line. For squares cut by a diagonal part of the line, you'll need to estimate the fraction of the square that's under the line
56
what is the gradient of the line in a velocity-time graph?
the acceleration - negative gradient means deceleration
57
what does a curved line mean in a velocity time graph?
that the acceleration is changing - if the line is curved, the acceleration is not constant - a steepening curve means the acceleration is increasing, and a flattening curve means the acceleration is decreasing.
58
what is the resultant force?
the sum of all the forces
59
what is Newton's first law? What does this mean?
Newton's First law states that the velocity of an object will not change unless a resultant force acts on it. This means an object will stay still or move in a straight line at a constant speed, unless there is a resultant force acting on it.
60
what does a resultant force cause an object to do?
accelerate in the direction of the force
61
what is Newton's Second Law?
Newton's second law states that the acceleration is directly proportional to the resultant force - F = ma
62
what is Newton's third law?
Newton's Third Law states that each force has an equal and opposite reaction force
63
what is the formula for kinetic energy?
Ek = 1/2 x m x v^2
64
what is the equation for gravitational potential energy?
Ep = mgh
65
what is gravitational field strength (g)?
the ratio of an object's weight to its mass (in newtons per kilobgram, Nkg^-1)
66
what is the principle of conservation of energy?
energy cannot be created or destroyed - it can only be converted into other forms
67
what is the amount of energy (in joules) that a force transfers called?
work done
68
what's the equation for work done?
work done by force (J) = size of force (N) x distance the object moves in the direction of the force while the force is acting (m)
W = fs
69
how do you calculate work done if the force isn't in the same direction as the movement? Include a real life example.
Sometimes the force acts in a different direction to the object's movement, e.g. when you pull on a sledge, the force acts diagonally along the rope but the sledge only moves horizontally.
You need to use some trigonometry to find the work done: W = Fcosθ x s
70
how do you work out the work done (from the energy in the stores that the work goes into) if the work goes into increasing both the kinetic and gravitational energy?
work done = increase in Ek + increase in Ep so:
Fs = (1/2 x m x v^2) + (mgh)
71
what is happening when energy is converted in mechanical situations? give an example
work is being done. For example, when an object is falling, the force of gravity is doing work on that object equal to the increase in kinetic energy (ignoring air resistance)
72
what is power?
the rate at which work is being done
73
Give 2 equations for power & include symbols
1. power (in watts) = work done (in joules) / time taken (in seconds)
P = W/t
2. power (in watts) = force (in newtons) x speed (in ms^-1)
P = Fv
74
what is power measured in? What is one of these measurements equivalent to?
power is measured in watts.
A watt is equivalent to one joule of work done per second.
75
when is the formula P = Fv true?
it is only true when the object is moving at a constant speed in the same direction as the force
76
why is P = F x v true?
power is given by P = W / t
W = Fs, so we can substitute for the work done, giving P = (F x s)/t. This is the same as F x s/t, so P = F x s/t.
s/t = distance travelled / time = the speed, v
77
how can you measure the efficiency of a system?
by the percentage of total energy put in that is converted to useful forms:
efficiency = (useful energy out / total energy in) x 100
78
define elastic objects
objects that return to their original shape after the deforming force is removed, e.g. springs.
79
what is Hooke's Law?
the extension (Δl) of a spring is directly proportional to the force applied (F). This relationship is also true for many other elastic objects like metal wires.
F = k x ΔL
However, Hooke's Law stops working when the force is great enough - there's a limit to the amount of force you can apply to an object for the extension to keep on increasing proportionally.
80
what is the equation for Hooke's Law? include units.
force (N) = spring constant (Nm^-1) x extension (m)
F = k x Δl
81
what does the spring constant depend on? What is it measured in?
the spring constant, k, depends on the stiffness of the material that you are stretching. It's measured in newtons per metre (Nm^-1)
82
what is the limit of proportionality (P)?
the maximum force that the spring can take and still extend proportionally.
83
what is the elastic limit (E)? What happens to the spring beyond the elastic limit?
if you increase the force past the elastic limit, the spring will be permanently stretched. When the force is removed, the spring will be longer than at the start. Beyond the elastic limit, we say that the spring deforms plastically.
84
where is the work done stored when a material is stretched, and when it stopped being stretched? What if a deformation is plastic?
- when a material is stretched, work has to be done in stretching the material
- if a deformation is elastic, all the work done is stored as elastic strain energy (also called elastic potential energy) in the material
- when the stretching force is removed, this stored energy is transferred to other forms - e.g. when an elastic band is stretched and then fired across a room, elastic strain energy is transferred to kinetic energy
- however, if a deformation is plastic, work is done to separate atoms, and energy is not stored as strain energy (it's mostly lost as heat)
85
what flows around a circuit and in which direction?
- negatively-charged electrons flow from the negative end of a battery to the positive end. this flow of charge is called electric current.
- however, you can also think of current as a flow of positive charge in the other direction, from positive to negative. THis is called conventional current.
86
how do you work out the electric current at a point in the wire?
current (A) = the amount of charge passing the point (C) / the time it takes for the charge to pass (s)
I = Q/t
87
explain what potential difference (Voltage) is. include an equation.
the energy per unit charge:
- in all circuits, energy is transferred from the power supply to the components
- the power supply does work on the charged particles, which carry this energy around the circuit
- the potential difference across a component is defined as the work done (or energy transferred) per coulomb of charge moved through the component:
potential difference across component (V) = work done (J) / charge moved (C)
V = W/Q
88
can charge be used up or increased in circuits? why?
charge is always conserved in circuits:
- as charge flows through a circuit, it doesn't get used up or lost
89
explain Kirchhoff's first law (current same everywhere in a series ciruit, and is shared between the branches of a parallel circuit)
- as charge flows through a circuit, it doesn't get used up or lost
- you can easily build a circuit in which the electric current can be split between two wires - two lamps connected in parallel is a good example
- because charge is conserved in circuits, whatever charge flows into a junction will flow out again
- since current is rate of flow of charge, it follows that whatever current flows into a junction is the same as the current flowing out of it
sum of the currents going into the junction = the sum of the currents going out
90
which direction of flow do arrows on circuit diagrams normally show?
the direction of flow of conventional current (from positive to negative)
91
give 2 things that are always conserved in circuits
1. charge
2. energy
92
what is Kirchoff's second law? What does it mean?
for any closed loop in a circuit, the sum of the potential difference across the components equals the potential difference of the power supply. This means that:
- in a series circuit, the potential difference of the power supply is split between all the components
- in a parallel circuit, each loop has the same potential difference as the power supply
93
explain Kirchhoff's second law (voltage in circuits)
energy is always conserved in circuits:
- energy is given to charged particles by the power supply and taken from them by the components in the circuit
- since energy is conserved, the amount of energy one coulomb of charge loses when going around the circuit must be equal to the energy it's given by the power supply
- this must be true regardless of the route the charge takes around the circuit. This means that:
for any closed loop in a circuit, the sum of the potential differences across the components equals the potential difference of the power supply
94
give an equation for resistance, include units
resistance of component (Ω) = potential difference across component (V) / current passing through component (A)
R = V/I
95
what does Ohm's law state?
potential difference is proportional to current - provided the temperature is constant, the current through an ohmic component (e.g. a resistor) is directly proportional to the potential difference across it.
96
what is an I-V graph?
a graph of current against potential difference for a component
97
describe the I-V graph of an ohmic component
it's a straight line, with a gradient equal to 1 / the resistance of the component. The resistance (and therefore the gradient) is constant
98
is Ohm's law always true for ohmic components?
often external factors, such as temperature, will have a significant effect on resistance, so you need to remember that Ohm's law is only true for components like resistors at constant temperature
99
what does an I-V graph with negative values for p.d. and current mean?
that the current is flowing the other way (so the terminals of the power supply have been switched)
100
what is power?
the rate of transfer of energy
101
what do components in electrical circuits do?
transfer the energy carried by electrons into other forms
102
give 2 equations to find the power in a circuit
1. P = (V x Q)/t
2. P = VI
103
give 2 equations for power that can be made by combining P = VI and R = V/I
1) P = I^2 x R
2) P = V^2 / R
104
Resistors get hotter when a current flows through them. If you double the current through a resistor, what happens to the amount of heat energy produced every second?
it increases by a factor of 4 - this is because the current is squared in the expression of power
105
what are waves? what do they do?
1. waves are oscillations that transfer energy - like water waves or electromagnetic waves
2. waves carry energy from one place to another without transferring matter
106
describe transverse waves, and give examples
transverse waves have vibrations at 90 degrees to the direction of energy transfer and travel. e.g. electromagnetic waves (like light) or waving a rope up and down
107
describe longitudinal waves, and give examples
longitudinal waves vibrate in the same direction as the direction of energy transfer and travel. They are made of alternate compressions and rarefactions of the medium. e.g. sound waves or pushing on the end of a slinky spring
108
which 2 types of graph do you use to map a wave? what do they show?
1. a displacement-distance graph shows how far each part of the wave is displaced from its equilibrium position for different distances along the wave
2. you can also consider just one point on a wave and plot how its displacement changes with time. This is a displacement-time graph
109
what is the amplitude (A) of a wave?
the largest possible displacement from the equilibrium position
110
what is a wavelength?
the length of one wave cycle, from crest to crest or trough to trough
111
what is the period (T) of a wave?
the time taken for a whole cycle (vibration) to complete, or pass a given point
112
what is frequency (when talking about waves)?
the number of oscillations 1 point on a wave completes every second
113
what is the equation for frequency?
frequency = 1/time period
f = 1/T
114
what is the wave equation? include units
speed (m/s) = frequency (Hz) x wavelength (m)
v = f x λ
115
what happens when two waves meet?
superposition:
1. if two waves meet (e.g. waves on a rope travelling in opposite directions), their displacements will briefly combine
2. they become one single wave, with a displacement equal to the displacement of each individual wave added together
3. this is called superposition
4. after combining, the waves then carry on as they were before
116
what happens if, during superposition, two crests meet? What is this called?
if two crests meet, the heights of the waves are added together and the crest height increases. This is called constructive interference because the amplitude of the superposed waves is larger than the amplitude of the individual waves
117
what happens if, during superposition, the crest of one wave meets the trough of another wave? What is this called, and why?
you subtract the trough depth from the crest height. So if the crest height is the same as the trough depth they'll cancel out. This is called destructive interference because the amplitude of the superposed waves is smaller than that of the individual waves.
118
what does it mean if waves are in phase?
two waves travelling in the same direction are in phase with each other when the peaks of one wave exactly line up with the peaks of the other, and the troughs of one wave exactly line up with the troughs of the other
119
what happens if two waves are superposed when they are in phase?
they interfere constructively. the combined altitude of the final wave is equal to the sum of the individual waves
120
what happens if two waves are superposed that exactly are out of phase
they interfere destructively. If the individual waves had the same amplitude originally, they will cancel each other out
121
what happens when a wave hits a boundary between one medium and another?
some (or nearly all) of the wave is reflected back
122
what is the angle of the incoming wave called? What is it measured from?
the angle of incidence - measured from the normal (an imaginary line running perpendicular to the boundary
123
what does the law of reflection state?
angle of incidence (i) = angle of reflection (r)
124
what is diffraction?
waves spreading out
125
when do waves diffract? What affects how much they diffract?
- waves spread out (diffract) at the edges when they pass through a gap or pass an object
- the amount of diffraction depends on the size of the gap relative to the wavelength of the wave. The narrower the gap, or the longer the wavelength, the more the wave spreads out
- a narrow gap is one about the same size as the wavelength of the wave. so whethe ra gap counts as narrow or not depends on the wave
126
what happens if a light is shone at a narrow slit about the same width as the wavelength of the light?
- the light diffracts
- this diffracted light forms a diffraction pattern of bright and dark fringes. This pattern is caused by constructive and destructive interference of light waves
127
what happens when you get diffraction around the edges of obstacles?
- a shadow is created
- the shadow is where the wave is blocked by the obstacle. The wider the obstacle compared to the wavelength, the less diffraction it causes, so the longer the shadow.
128
what happens if a wave hits a boundary face on?
it slows down without changing direction
129
what happens if a wave hits a boundary at an angle?
one part of the wave slows down while the other part carries on moving at the same speed, causing the wave to change direction as well as slowing down
130
which way does an electromagnetic wave bend when it enters a denser medium, compared to a less dense medium?
when an electromagnetic wave enters a denser medium, it bends towards the normal. When one enters a less dense medium, it bends away from the normal
131
what is the refractive index of a medium (n)?
the ratio of the speed of light in a vacuum to the speed of light in that medium. Every transparent material has a refractive index and different materials have different refractive indices
132
how can you calculate the refractive index?
using Snell's law:
- when an incident ray travelling in air meets a boundary with another material, the angle of refraction of the ray, r, depends on the refractive index of the material and the angle of of incidence, i.
- this is called Snell's Law: refractive index (n) = sin(i) / sin(r)
133
name the 2 nucleons
protons & neutrons
134
what is the relative mass of an electron?
0.0005 (5x10^-4)
135
how can atomic structure be represented?
using nuclide notation
136
how does nuclide notation work?
1. the proton number (or atomic number), Z, is the number of protons in an atom
2. the nucleon number (or mass number), A, is the total number of protons and neutrons
A element
Z symbol here
137
what is the radioactive decay of carbon-14 used for?
it's used in radiocarbon dating to estimate the age of things that are thousands of years old
138
what can happen if an atom is unstable? what does this lead to?
it can undergo radioactive decay and give off nuclear radiation. By decaying, a nucleus emits particles or energy, leading to the atom becoming more stable
139
give the 3 kinds of nuclear radiation
1. alpha decay
2. beta decay
3. gamma degay
140
what is emitted in alpha decay, and what is the symbol for it?
in alpha decay (symbol α), an alpha particle is emitted from the nucleus. It is made up of two protons and two neutrons
141
what happens to the proton and nucleon numbers of an atom when an alpha particle is emitted?
the proton number goes down by 2 and the nucleon number goes down by 4.
142
what is the symbol for beta decay? what does it emit, and how does this happen?
in beta decay (symbol β), an electron is emitted from the nucleus - a neutron in the nucleus turns into a proton and an electron. The electron is emitted from the nucleus and is called a beta particle.
143
what happens to the proton and nucleon numbers of the atom when a beta particle is emitted?
the proton number goes up by 1, and the nucleon number doesn't change
144
what is the symbol for gamma decay? what does it emit?
in gamma decay (symbol γ), high-energy electromagnetic radiation, called gamma radiation, is emitted from the nucleus.
145
how do you plan an experiment?
1. make a prediction or hypothesis - a testable statement about what you think will happen
2. identify any variables
3. think about any risks, and how you can minimise them
4. select the right equipment for the job - if you're measuring a time interval in minutes you might use a stopwatch, but if it's in milliseconds you may need to get a computer to measure the time for you, as your reaction time could interfere with your results.
5. decide what data you need to collect and how you;ll do it.
6. write a clear, detailed method describing exactly what you're going to do.
146
what is a variable?
anything that has the potential to change in an experiment
147
what is the easiest way to see any patterns or trends in the results of an experiment?
using graphs
148
what are the three types of correlation data can show?
1. positive correlation
2. negative correlation
3. no correlation
149
what does correlation describe?
the relationship between the variables.
150
what does positive correlation mean?
as one variable increases, the other also increases
151
what does negative correlation mean?
as one variable increases, the other decreases
152
what does it mean if there is no correlation?
there is no relationship between the variables
153
give 2 things you should take into consideration when forming a conclusion
1. Your conclusion should be limited to what you've actually done and found out in your experiment. For example, if you've been investigating how the force applied to a spring affects how much it stretches, and hove only used forces between 0 and 5 N, you can't claim to know what would happen if you used a force of 10 N, or if you used a different spring
2. you also need to think about how much you can believe your conclusion, by evaluating the quality of your results. If you can't trust your results, you can't form a strong conclusion.
154
how can you estimate the uncertainty of a result if it isn't stated (and it wasn't you that performed the experiment)?
the number of significant figures gives you an estimate of the uncertainty. For example, 72 ms^-1 has 2 significant figures, so without any other information you know that this value be 72 ± 0.5 ms^-1, as if it was greater than 72.5 ms^-1 it would have been rounded to 73 ms^-1
155
what notation do you use to display the uncertainty of a result?
the ± symbol - e.g. 74 cm ± 0.5 cm
156
what is the measure of uncertainty of a ruler? How would you show this when wrriting a measurement?
if you measure a length with a ruler, you can only measure it to the nearest millimetre, as that's the smallest difference marked on the ruler's scale. If you measure a length with a ruler as 14 mm you can write this as 14 ± 0.5 mm to show that you could be up to half a millimetre out either way
157
give 3 questions you should ask yourself when thinking about how your experiment could be improved
1. did the experiment actually test what it was supposed to? Could you make it more relevant to the question?
2. Was there anything you could have done to prevent some of the errors in your results?
3. Would different apparatus or a different method have given you better results?
