paper 1 Flashcards
1
Q
distance time graphs
A
A constant gradient represents constant speed
The gradient of the line represents the speed:
A very steep gradient means the object is moving at a large speed
A shallow gradient means the object is moving at a small speed
A flat, horizontal line means the object is stationary (not moving)
Objects might be accelerating - this is represented by a curve
In this case, the gradient of the line will be changing
If the gradient is getting steeper, the speed is increasing (accelerating)
If the gradient is getting shallower, the speed is decreasing (decelerating)
The speed of a moving object can be calculated from the gradient of the line on a distance-time graph
2
Q
speed, distance and time equation
A
speed = distance / time
3
Q
practical: investigate the motion of everyday objects such as toy cars or tennis balls
A
Measure out a height of 1.0 m using the tape measure or metre ruler
Drop the object from this height, which is the distance travelled by the object
Use the stop clock to measure how long the object takes to travel this distance
Record the distance travelled and time taken
Repeat steps 2-3 three times, calculating an average time taken for the object to fall a certain distance
Repeat steps 1-4 for heights of 1.2 m, 1.4 m, 1.6 m, and 1.8 m
4
Q
acceleration, time taken and change in velocity equation
A
acceleration = change in velocity / time taken
5
Q
velocity time graphs
A
The gradient of the line represents the magnitude of acceleration
A steep gradient means large acceleration
A shallow gradient means small acceleration
A positive gradient (upward slope) shows increasing velocity -> acceleration
A negative gradient (downwards slope) shows decreasing velocity -> deceleration
A horizontal line means the acceleration is zero so the object is moving with a constant velocity
6
Q
how to find acceleration from a velocity time graph
A
calculated from gradient of the line
7
Q
how to find the distance traveled on a velocity time graph
A
find the area under the line
8
Q
what does kg measure
A
mass
9
Q
what does N/kg measure
A
gravitational field strength or acceleration due to gravity
10
Q
what are the effects of forces between bodies
A
When a force acts on an object, the force can affect the object in a variety of ways
The object could:
change speed
change direction
change shape
11
Q
types of forces
A
Gravitational (or weight) - the force between any two objects with mass (like the Earth and the Moon)
Electrostatic - the force between any two objects with charge (like a proton and an electron)
Thrust - the force pushing a vehicle (like the push from rocket engines on the shuttle)
Upthrust - the upward force on any object in a fluid (like a boat on the surface of a river)
Air resistance (or drag) - the force of friction between objects falling through the air (like a skydiver in freefall)
Compression - forces that squeeze an object (like squeezing a spring)
Tension - forces that stretch an object (like two teams in a tug-of-war)
Reaction force - the force between any two objects in contact (like the upwards force from a table on a book)
12
Q
what is the difference between vectors and scalers
A
Scalars are quantities that have magnitude but not direction
Vectors are quantities that have both magnitude and direction
13
Q
examples of vectors
A
displacement
force
weight
velocity
acceleration
momentum
14
Q
what is a force that opposes motion
A
friction
Frictional forces always act in the opposite direction to the object’s motion
Friction occurs when two (or more) surfaces rub against each other
At a molecular level, both surfaces contain imperfections - i.e. they are not perfectly smooth
These imperfections push against each other
15
Q
examples of scalers
A
distance
speed
mass
energy
temperature
16
Q
force, acceleration and mass equation
A
force = mass x acceleration
17
Q
weight, mass and gravitational field strength equation
A
weight = mass x gravitational field strength
18
Q
what is the stopping distance
A
thinking distance + braking distance
19
Q
what factors affect the vehicles stopping distance
A
speed
mass of car
condition of cars breaks
road condition
reaction time
20
Q
forces acting on falling objects
A
Weight
Air resistance
The force of air resistance increases as the object’s speed increases
This is because the object collides with air particles as it moves through the air
The faster the object is travelling, the more collisions it has with the air particles
21
Q
terminal velocity
A
Terminal velocity is the fastest speed that an object can reach when falling
Terminal velocity is reached when the upward and downward acting forces are balanced
The resultant force on the object reaches zero
The object no longer accelerates and a constant terminal velocity is reached
22
Q
skydiver example of terminal velocity
A
At the instant the skydiver steps out of the plane, the support force of the plane is no longer acting on the skydiver, but they are not yet falling, so the only force exerted them is the weight force
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force
The skydiver accelerates downward at maximum acceleration
As the skydiver begins to fall, the force of air resistance is very small because the skydiver’s speed is small
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force minus the force of air resistance
The skydiver accelerates downward but the acceleration decreases
As the skydiver accelerates, their speed increases, so the force of air resistance increases
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force minus the force of air resistance
The skydiver accelerates downward but the acceleration continues to decrease
As the skydiver’s acceleration decreases, their speed increases at a slower and slower rate
Eventually, the skydiver reaches a speed at which the force of air resistance is equal to the force of weight
The forces are balanced, so the resultant force is zero
The skydiver no longer accelerates and a constant velocity is reached
This is terminal velocity
23
Q
equation with initial speed, final speed, distance moved and acceleration
A
(final speed)^2 = (initial speed)^2 + (2 x acceleration x distance moved)
24
Q
how to calculate the resultant force that acts along a line
A
largest force - smallest force
25
Practical: investigate how extension varies with applied force for helical springs, metal wires and rubber bands
1. set up a clamp and stand with a G-clamp holding it to the desk so the clamp doesn't fall over
2. strap a ruler to the stand so the 0 is aligned with the bottom of the spring when it is hanging
3. add a 100g mass onto the spring
4. record the mass (kg) and the extension of the spring (cm)
5. repeat 3+4 until all masses have been added
6. remove all masses and repeat whole process 3x and calculate mean for average length of extension
extension is the distance the bottom of the spring has moved from where the bottom originally was
NEED TO WEAR GOGGLES incase spring snaps
don't stand below the weights incase they fall
26
Hooke's Law
The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality
27
force - extension graphs
Hooke's law on a graph is only the part where the line is straight and goes through the origin (proportional)
when the line is no longer straight then the object does not obey Hooke's law and it has gone beyond its limit of proportionality
28
elastic deformation
where the object does return to its original shape after the force has been removed
29
plastic/inelastic deformation
where an object does not return to its original shape after force is removed
30
whats an amp (A)
the number of coulombs per second (the number of charge flowing per second)
eg 1 amp = 1 coulomb per second
31
whats a coulomb (C)
a unit of charge
32
whats a joule (J)
a unit of energy
33
whats a ohm (Ω)
a unit of resistance
34
what is a second (s)
a unit of time
35
what is a volt (V)
the amount of energy per each unit of charge
eg 1 volt = 1 joule per coulomb
36
what is a watt (W)
the amount of energy supplied per second
eg 1 watt = 1 joule per second
37
why are electrical appliances insulated
the part of the appliance where the current flows is made of metal so if it comes into conduct with a person it could give an electric shock
38
what is insulation and how does it protect the user
covering a wire with an insulating material and so it will prevent the current entering the body by being a physical barrier from the live wire carrying the current
39
what is double insulation
an appliance which does not have a metal case is 'double insulated'
example:
Insulation around the wires themselves
A non-metallic case that acts as a second layer of insulation
the case being made out of an insulator means that even if there is a fault and the live wire touches the case then the user is still protected because the case is an insulator so it won't conduct
40
why does a double insulated appliance not need a earth wire
because the case will never become live (as its made of an insulator) so there will never be need to remove the charge from the case
41
what is an earth wire
it is connected to the metal case of a appliance and it provides a low resistance (high current) path to the earth
42
how does the earth wire protect a user
if there is a fault and current is flowing in the case of an appliance (dangerous) then:
the earth wire provides a low resistance path to the earth
It causes a surge of current (because the earth wire is low resistance high current) in the earth wire and hence also in the live wire
The high current through the fuse causes it to melt and break
This cuts off the supply of electricity to the appliance, making it safe
43
what is a fuse
a piece of thin metal wire that is part of a circuit so if there is a rise in current it will melt breaking the circuit and stopping the current
44
what is a circuit breaker
an automatic electromagnet switch that switches off if the circuit is the current exceeds a certain value
45
how does a fuse or circuit breaker protect a user
if there is too much current flowing in a circuit this is dangerous because there will be more heat which means there could be a fire.
the fuse or circuit breaker stops this from happening because they will break the circuit if too much current is flowing preventing this
46
equation between Current, power, voltage
power = voltage x current
p = VI
47
equation between current, energy transferred, voltage, time
energy transferred = current x voltage x time
E = IVt
48
what happens when a current flows through a resistor
During their journey through the resistor, the electrons collide with ions in the resistor material.
These collisions result in friction, converting electrical energy into thermal energy (heat).
so when the current flows through the resistor the energy is changed into thermal energy which leads to an increase in temperature
49
how can a resistor be used in domestic contexts
Joule heating or Ohmic heating
electric heaters
electric ovens
electric stoves
toasters
50
what is resistance
As the electrons pass through the metal lattice (wire) they collide with ions
The ions resist the flow of the electrons
51
what is AC
A current that continuously changes its direction, going back and forth around a circuit (mains electricity)
52
what is DC
A current that is steady, constantly flowing in the same direction in a circuit, from positive to negative (a cell or battery)
53
advantages of a series circuit
simple to construct
less likely to overheat
54
disadvantages of a series circuit
if one component fails then the whole circuit won't work
55
advantages of a parallel circuit
if one component fails the rest will still work
components have a higher voltage
56
disadvantages of a parallel circuit
more likely to overheat
57
is a series or parallel circuit better for domestic lighting
parallel
Each light operates independently, ensuring that a single bulb failure does not darken the entire room.
You can add or remove lights without affecting the others.
can also switch off one light and leave the rest on
58
current in series
the current is the same everywhere in the circuit
current will increase if there more voltage or less components
59
voltage in series
The voltage across all of the components adds up to the supply voltage from the cell
60
current in parallel
the current splits at junctions
the current in each of the branches adds up to the total current leaving the cell
61
voltage in parallel
the total voltage of the cell applies to each section of the circuit
the voltage across two components connected in parallel is the same
62
whats the relationship between the current and voltage and resistance
as voltage increases so does current
as resistance increases current decreases
63
what is the relationship between current and voltage in wires
if you increase the voltage across a wire, the current through the wire will increase, provided the resistance remains constant. Similarly, if you decrease the voltage, the current will decrease. This relationship is directly proportional for a given resistance
64
what is the relationship between current and voltage in resistors
if you increase the voltage across a resistor, the current through the wire will increase, provided the resistance remains constant. Similarly, if you decrease the voltage, the current will decrease. This relationship is directly proportional for a given resistance
65
what is the relationship between current and voltage in filament lamps
for a filament lamp, current and voltage are not directly proportional
This is because the resistance of the filament lamp increases as the temperature of the filament increases
As the current increases, the temperature of the filament in the lamp increases
The higher temperature causes the ions in the metal lattice of the filament to vibrate more
This causes an increase in resistance as it becomes more difficult for free electrons (the current) to pass through
Resistance opposes the current, causing the current to increase at a slower rate
66
what is the relationship between current and voltage in diodes
When the current is in the direction of the arrowhead symbol, this is forward bias (allows the current to flow only in one direction)
This is shown by the sharp increase in potential difference and current on the right side of the graph
When the diode is switched around, this is reverse bias (in reverse direction there is very high resistance and so no current flows)
This is shown by a zero reading of current or potential difference on the left side of the graph
67
how to investigate how the current changes with voltage
create a circuit with
- a component (eg lamp)
- a ammeter to measure current (added in series)
- a voltmeter to measure voltage (added in parallel)
- a variable resistor to change the current (added in series)
- a cell
68
how does resistance change with Light dependent resistor
as light intensity increases, resistance decreases inversely proportional
69
how does resistance change with thermisters
as temperature increases, resistance decreases inversely proportional
70
what can a lamp or LED indicate
if it turns on then it indicates a current in the circuit
71
formula with current, voltage, resistance
voltage = current x resistance
V=IR
72
what is the current
the rate of flow of charge
73
formula with current, charge, time
charge = current x time
Q=It
74
what is current measured in
amps (A)
75
what is charge measured in
coulombs (C)
76
what is energy measured in
joules (J)
77
what is resistance measured in
ohms (Ω)
78
what is voltage measured in
volts (V)
79
what is power measured in
watts (W)
80
what is electric current in solid metallic conductors
a flow of negatively charged electrons
81
why is current conserved at a junction in a circuit
current in electrical circuits is made up of charge and charge must be conserved (can't add or take away)
82
what is voltage
the amount of energy transferred per unit of charge
a volt is a joule per coulomb
83
formula with charge, energy transferred, voltage
energy transferred = charge x voltage
E=QV
84
what is the effect of changing the resistance on the current in a circuit
If the resistance increases while the voltage stays the same, the current decreases. This is because the current (I) is inversely proportional to the resistance (R).
85
what is hertz measuring
the frequency of something
86
what is the frequency of a wave
the amount of cycles per second
the number of waves that pass a fix point per second
the pitch
87
longitudinal waves
the waves oscillate in the parallel (same direction) to the direction they travel in
88
transverse waves
the waves oscillate perpendicular (at right angles) to the direction they travel in
89
examples of longitudinal waves
sound waves
seismic p-waves
spring/slinkie
90
examples of transverse waves
electromagnetic waves
ripples in the sea
mexican wave
seismic s-waves
rope
91
what is the amplitude of a wave
The distance from the undisturbed position to the peak or trough of a wave
the volume
92
what is the wavefront of a wave
the wavefront is a way of drawing a wave from above (all of the waves are drawn in the same phase, eg all troughs)
each line represents one wave and if they are close together that shows a high frequency
93
what is the wavelength of a wave
The distance from one point on the wave to the same point on the next wave
94
what is the period of a wave
the time it takes for one wavelength to happen
95
what do waves transfer
transfer energy and information, without transferring matter
96
what is the formula with wavelength, frequency, wave speed
wave speed = frequency x wavelength
v=fλ
97
what is the formula with frequency and time period
frequency = 1 / time period
f=1/T
98
what does the doppler effect change
the change in wavelength and frequency of a wave emitted by a moveing source
99
why does the doppler effect change the frequency of a wave
When the source of the wave is moving towards the observer, each successive wave cycle is emitted from a position closer to the observer than the previous cycle. As a result, the time between the arrival of each wave at the observer is reduced, which effectively increases the frequency of the wave as observed by the observer2.
Conversely, if the source of the wave is moving away from the observer, each wave cycle is emitted from a position farther from the observer than the previous cycle. This increases the time between the arrival of each wave at the observer, effectively reducing the observed frequency
100
why does the doppler effect change the wavelength of a wave
When the source of the wave is moving towards the observer, each successive wave cycle is emitted from a position closer to the observer than the previous cycle1. This causes the wavefronts to “bunch up”, effectively shortening the wavelength as observed by the observer3. This is why waves appear “squeezed” or “compressed” when the source is moving towards the observer4.
Conversely, if the source of the wave is moving away from the observer, each wave cycle is emitted from a position farther from the observer than the previous cycle1. This causes the wavefronts to spread out, effectively lengthening the wavelength as observed by the observer3. This is why waves appear “stretched out” when the source is moving away from the observer
101
can all waves be reflected or refracted
yes in the right circumstances
102
what type of wave is light waves
transverse
103
can light waves be reflected or refracted
yes
104
what is the law of reflection
The law of reflection states that the angle of incidence (the angle at which the wave hits the surface) equals the angle of reflection (the angle at which the wave bounces off the surface).
105
what is reflection
A wave hits a boundary between two media and does not pass through, but instead stays in the original medium
where angle i = r
106
what is the formula with refractive index, angle of incidence, angle of refraction
refractive index = sin(angle of incidence) / sin(angle of refraction)
n = sin(i) / sin(r)
107
practical: To investigate the refraction of light using rectangular blocks, semi-circular blocks and triangular prisms
Place the block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
Switch on the ray box and direct a beam of light at the side face of the block
Mark on the paper:
- A point on the ray close to the ray box
- The point where the ray enters the block
- The point where the ray exits the block
- A point on the exit light ray which is a distance of about 5 cm away from the block
Draw a dashed line normal (at right angles) to the outline of the block where the points are
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
Repeat the procedure for each shape of perspex block (prism and semi-circular)
108
practical: investigate the refractive index of glass using a glass block
Place the glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
Switch on the ray box and direct a beam of light at the side face of the block
Mark on the paper:
- A point on the ray close to the ray box
- The point where the ray enters the block
- The point where the ray exits the block
- A point on the exit light ray which is a distance of about 5 cm away from the block
Draw a dashed line normal (at right angles) to the outline of the block where the points are
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
measure the angle of incidence and angle of refraction and then use n = sin(i) / sin(r)
109
what is total internal reflection
Total Internal Reflection (TIR) is where waves arriving at the boundary from one medium to another (e.g., from water to air) are not refracted into the second (“external”) medium, but completely reflected back into the first (“internal”) medium
110
when does total internal reflection happen
The angle of incidence is greater than the critical angle and the incident material is denser than the second material
111
what are the conditions needed for total internal reflection
The angle of incidence > the critical angle
higher refractive index than air
when a ray tries to go from a denser to a less dense material
112
how is total internal reflection used in optical fibres
they are made of glass or plastic with in outer cladding which has a lower refractive index than the glass
which means that the light will always hit a boundary at a higher value than the critical angle
the light waves are totally internal reflected down whole wire meaning all of the wave reaches the other end which allows all of the information to to be passed through the fibre without any being lost
113
what is the critical angle
the angle where the light is refracted along the boundary of the surface
As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90°
When the angle of refraction is exactly 90° the light is refracted along the boundary
At this point, the angle of incidence is known as the critical angle c
after this point tir occurs
114
what is the formula with critical angle and refractive index
sin(critical angle) = 1 / refractive index
sin(c)=1/n
115
what type of wave is a sound wave
longitudinal waves
116
can sound waves be reflected and refracted
yes
117
what happens to a wave if it enters a more dense material at an angle
it will bend towards the normal
118
what happens to a wave if it enters a less dense material at an angle
it will bend away from the normal
119
what is light part of
a continuous electromagnetic spectrum that includes radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations, and that all these waves travel at the same speed in free space
120
order of the EM spectrum, in terms of decreasing wavelength and increasing frequency
low energy, long wavelength, low frequency
radio
microwaves
infared
visible
ultraviolet
xray
gamma
high energy, short wavelength, high frequency
121
order of colours of the visible spectrum
longest wavelength, low frequency
red
orange
yellow
green
blue
indigo
violet
short wavelength, high frequency
122
uses of radiowaves
broadcasting and communications
123
uses of microwaves
cooking and satellite transmissions
124
uses of infrared
heating and night vision equipment
125
uses of visible light
photography + optical fibres
126
uses of ultraviolet
fluorescent lamps + tanning beds
127
uses of xrays
observing internal structure of objects and materials including for medical uses
128
uses of gamma rays
sterilising food and medical equipment
treating cancer
129
effects of excessive exposure of microwaves
internal heating of body tissue -> prevented with metal walls and metal grid in glass door
130
effects of excessive exposure of infrared
surface skin cell burns -> prevented with protective clothing
131
effects of excessive exposure of ultraviolet
damage to surface skin cells and blindness -> prevented with sunglasses for eyes and suncream for skin
132
effects of excessive exposure of gamma rays
cancer + mutation -> prevented with minimal exposure and lead clothing
133
effects of excessive exposure of xrays
cancer + mutation -> prevented with minimal exposure and lead clothing
134
effects of excessive visible light wave exposure
vision impairments -> don't look into the sun and wear sunglasses
135
what speed do waves travel at in a vacuum
all travel at speed of light
136
what are the 8 energy stores
chemical
kinetic
gravitational
elastic
themal
magnetic
electrostatic
nuclear
137
what are the 5 energy transfers
mechanically
electrically
radiated sound
ratdiated light
by heating
138
what is the principle of conservation of energy
energy cannot be created or destroyed only transferred from one form to another
139
what is the formula with work, distance moved, force
work = force x distance moved
W = F x d
140
is work done and energy transferred equal
yes
141
what is the formula with gravitiational potential energy, mass, height, gravtiational field strength
gravitiational potential energy = mass x gravitiational field strength x height
GPE = mgh
142
what is the formula for kinetic energy
kinetic energy = 1/2 x mass x speed^2
KE = 1/2mv^2
143
how does conservation of energy produce a link between GPE, KE and work done
if an object falls GPE -> KE and the change in GPE = work done
if an object is thrown up, KE -> GPE and the change in KE = work done
this means that (assuming there is no air resistance) GPE + KE = constant
They are different forms of energy that can be transformed into each other while keeping the total energy constant
144
what is power
the rate of transfer of energy or the rate of doing work
145
what is the formula with work done, time taken, power
power = work done / time taken
P = W / t
146
formula for efficiency
efficiency = useful energy output / total energy output x 100
147
how does thermal energy transfer take place
conduction or convection or radiation
148
how does conduction work
When a substance is heated, the atoms start to move around (vibrate) more
As they do so they bump into each other, transferring energy from atom to atom
Metals are especially good at conducting heat as the delocalised electrons can collide with the atoms, helping to transfer the vibrations through the material and hence transfer heat better
149
how does radiation energy transfer work
When an object has thermal energy, it emits radiation in the form of electromagnetic waves. The amount and type of radiation depend on the object’s temperature and surface properties.
150
how does convection work
When a fluid (a liquid or a gas) is heated:
The molecules push each other apart, making the fluid expand
This makes the hot fluid less dense than the surroundings
The hot fluid rises, and the cooler (surrounding) fluid moves in to take its place
Eventually, the hot fluid cools, contracts and sinks back down again
The resulting motion is called a convection current
Convection is the main way that thermal energy is transferred through liquids and gases
Convection cannot occur in solids
151
explain how emission and absorption of radiation are related to surface and temperature
black - good absorber and emitter
dull - ok absorber and emitter
white - poor absorber and emitter
shiny - awful absorber and emitter
152
practical: investigate thermal energy transfer by conduction
Attach ball bearings to the ends of each metal strip (different metal) at an equal distance from the centre, using a small amount of wax
The strips should then be turned upside down and the centre heated gently using a bunsen burner so that each of the strips is heated at the central point where they meet
When the heat is conducted along to the ball bearing, the wax will melt and the ball bearing will drop
Time how long this takes for each of the strips and record in a table
Repeat the experiment and calculate an average of each time
Order the metals according to their thermal conductivity
The first ball bearing to fall will be from the rod that is the best thermal conductor
This is because materials with high thermal conductivity heat up faster than materials with low thermal conductivity
153
ways of reducing unwanted energy transfer
to stop conduction: surround with an insulator such as wool as its molecular structure does not allow the particles to vibrate and so stops them bumping into each other and transferring energy
to stop radiation: surround in white shiny wrap as this will reflect the infrared waves back into the source stopping energy being lost
to stop convection: use something with air pockets as the confined pockets prevent a large convection current starting up
154
practical: investigate thermal energy transfer by convection
Fill the beaker with cold water (not too full) and place it on top of a tripod and heatproof mat
Pick up the crystal using forceps and drop it into the centre of the beaker – do this carefully to ensure the crystal does not dissolve prematurely
Heat the beaker using the Bunsen burner and record observations
Repeat experiment with hot water and record observations
Energy is initially transferred from the Bunsen flame through the glass wall of the beaker by conduction
The water in the region of the Bunsen flame is heated and the space between the water molecules expands, therefore, the water becomes less dense and rises
This causes the dissolved purple crystal to flow upwards with the water
Meanwhile, when the water at the top of the beaker cools, there is less space between the water molecules and the water becomes denser again and falls downwards
The process continues which leads to a convection current where energy is transferred through the liquid
The dissolved purple crystal follows this current which can be clearly observed during this experiment
155
practical: investigate thermal energy transfer by radiation
Set up the four identical flasks painted in different colours: black, grey, white and silver
Fill the flasks with hot water, ensuring the measurements start from the same initial temperature
Note the starting temperature, then measure the temperatures at regular intervals, e.g. every 30 seconds for 10 minutes
All objects emit infrared radiation, but the hotter an object is, the more infrared waves are emitted
The intensity (and wavelength) of the emitted radiation depends on:
The temperature of the body (hotter objects emit more thermal radiation)
The surface area of the body (a larger surface area allows more radiation to be emitted)
The colour of the surface
Most of the energy lost from the beakers will be by heating due to conduction and convection
This will be equal for each beaker, as colour does not affect energy transferred by conduction and convection
Any difference in energy transferred away from each beaker must, therefore, be due to infrared radiation
To compare the rate of energy transfer away from each flask, plot a graph of temperature on the y-axis against time on the x-axis and draw curves of best fit
156
why does hot air rise
air expands (the distance between the molecules increases) when it is hot causing it to decrease in density so rises
157
what does kg/m3 measure
density
158
what does pascal measure
pressure
159
formula for density
density = mass / volume
160
practical: investigate density using direct measurements of mass and volume with regularly shaped objects
Place the object on a digital balance and note down its mass
Use either the ruler, Vernier callipers or micrometre to measure the object’s dimensions (width, height, length, radius) – the apparatus will depend on the size of the object
Repeat these measurements and take an average of these readings before calculating the density
161
practical: investigate density using direct measurements of mass and volume with irregularly shaped objects
Place the object on a digital balance and note down its mass
Fill the eureka can with water up to a point just below the spout
Place an empty measuring cylinder below its spout
Carefully lower the object into the eureka can
Measure the volume of the displaced water in the measuring cylinder
Repeat these measurements and take an average before calculating the density
162
practical: investigate density using direct measurements of mass and volume with a liquid
Place an empty measuring cylinder on a digital balance and note down the mass
Fill the cylinder with the liquid and note down the volume
Note down the new reading on the digital balance
Repeat these measurements and take an average before calculating the density
163
formula for pressure
pressure = force / area
164
how does pressure at a point in a fluid act
When an object is immersed and stationary in a fluid, the fluid will exert pressure, squeezing the object
This pressure is exerted evenly across the whole surface of the fluid and in all directions
The pressure exerted on objects in fluids creates forces against surfaces
These forces act at 90 degrees (at right angles) to the surface
fluid is a liquid or a gas
165
equation for pressure difference
pressure difference = height x density x gravitational field strength
166
explain how molecules in a gas have random motion and that they exert a force, and hence a pressure, on the walls of a container
Molecules in a gas are in constant random motion at high speeds
Brownian motion provides evidence that air is made of small particles
This is because when larger particles, such as smoke particles or pollen, are observed floating in the air:
the larger particles move with random motion
this is a result of the larger particles colliding with smaller particles (which push the larger particles) that are invisible to the naked eye
As the gas particles move about randomly they collide with the walls of their containers
These collisions produce a net force at right angles to the wall of the gas container (or any surface)
and a force exerted over an area creates pressure (on the container walls)
167
why is there an absolute zero temperature
temperature refers to the amount of kinetic energy that the particles in the air have
so absolute 0 is where the particles have 0 energy and therefore are stationary and can't move any slower so the temperature cannot decrease anymore
168
kelvin temperature
kelvin -> centigrade (-273)
centigrade -> kelvin (+273)
kelvin cannot be negative
0 kelvin is absolute 0
kelvin refers to the average amount of energy the particles have
169
why does an increase in temperature result in an increase in average kinetic energy of the particles
increase in temperature means each particle moves faster so gains kinetic energy. So then the particles collide more frequently with each other and the container leading to an increase in pressure
170
relationship between kelvin temperature and average kinetic energy of the particles
proportional
171
formula with pressure and kelvin temperature
p1 = p2
T1 = T2
172
formula with pressure and volume
p1 x V1 = p2 x V2
173
relationship between pressure and volume at a constant temperature and why
For a fixed temperature, if the volume decreases, the pressure will increase
The particles travel the same speed as before, but the distance they travel is reduced when the container is smaller
The molecules will hit the walls of the container more frequently
This creates a larger overall net force on the walls which increases the pressure
pressure and volume are inversely proportional
174
relationship between pressure and kelvin temperature at a constant volume
If the temperature of the gas increases, the molecules will travel at a higher speed
This means they will collide with the walls more often
This creates an increase in pressure
pressure and temperature are proportional
175
what do magnets do
attract or repel other magnetic substances
176
what are the properties of a magnetically hard material
not easily magnitised or demagnitised
once it is magnetised it will stay magnetised for a long time even once the external field is removed
177
what are the properties of a magnetically soft material
easily magnetised and unmagnetised
won't stay magnetised once the external field is removed
178
examples of a magnetically hard material
steel
179
examples of a magnetically soft material
iron
180
what is a magnetic field line
The region around a magnet where a force acts on another magnet or on a magnetic material
181
how is magnetism induced
it is induced in certain materials when they are placed in a magentic field
182
practical: investigate the shape and direction of the magnetic field around a bar magnet
place the magnet on a piece of paper
Draw a dot at one end of the magnet (near its corner)
Place a plotting compass next to the dot, so that one end of the needle of the compass points away from the dot
Use a pencil to draw a new dot at the other side of the compass needle
Move the compass so that it points away from the new dot, and repeat the process above
Keep repeating the previous process until there is a chain of dots going from one end of the magnet to the other
Then remove the compass, and link the dots using a smooth curve – this will be the magnetic field line
183
practical: investigate the shape of a magnetic field around a bar magnet
place the magnet on a piece of paper
gently scatter iron filings around the magnet
gently tap the piece of paper and the iron will move into the shape of the field
184
how to use 2 permenant magnets to form a uniform magnetic field
place the 2 magnets a few centimeters apart
have the north of one magnet point to the south of the other magnet and have them aligned
185
how to draw a uniform magnetic field
straight evenly spaced lines pointing from north to south
186
what does an electric current in a conductor produce
a magnetic field
187
what is flemings left hand rule
left hand
thumb represents the direction in which the force will act on the wire
first finger - the direction the magnetic field runs in (north to south)
middle finger - the direction the current is going in (+ -> -)
188
why is a force exerted on a current carrying wire in a magnetic field
the 2 magnet field (existing one + wire) interact
a force will act on the wire
189
how is d.c. used to create simple electric motors
Current flows in the wire/coil.
This creates a magnetic field around the wire/coil.
This magnetic field interacts with the field from the permanent magnet.
This produces a force on the wire/coil which moves the wire/coil.
equal forces in opposite directions produce a turning movement so the coil spins
The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning.
190
how is a.c. used to create simple loudspeakers
a cone is placed on the south pole of a circular magnet
the cone is wrapped in wire coils which are connected to a AC power supply
as current is passed through the wire it generates an magnetic field
the two fields interact and produce a force which causes the cone to oscillate
when the current switches direction the force on the cone reverses
this causes the cone to move in and out and generate sound waves
by changing the frequency of the AC supply we can change the frequency that the cone vibrates
the vibrations create sound waves
by increasing the current we increase the amplitude and loudness
191
how does the force on a current carrying conductor (eg wire) in a magnetic field change with the magnitude and direction of the field and current
If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire.
If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire
if you wind more coils of wire that will also increase the force
192
what is electromagnet induction
when a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it
193
what factors change the size of voltage induced in electromagnetic induction
use a stronger magnet
use more coils of wire
move the wire faster through the magnetic field
194
how can electricity be generated by using electromagnetic induction
by rotating a magnet within a coil of wires
by rotating a coil of wires within a magnet
195
what is a becquerel
the amount of times something decays per second
1 Bq = 1 decay per second
196
what is a nucleon
a particle in the nucleus of a atom
proton and neutrons aka the mass number
197
what does the atomic number refer to
the number of protons an atom has
198
what does the mass number refer to
the weight of a atom
the number of protons and neutrons
199
what is a isotope
a element with the same number of protons (and electrons) but a different number of neutrons
200
how are alpha, beta and gamma particles emitted
from a unstable nucleus in a random process
201
what are alpha, beta and gamma particles
highly ionising radiations
202
what is a alpha radiation particle
a helium nucleus -> 2 protons + 2 neutrons
203
what is a beta particle
an fast moving electron
204
what is a gamma radiation
a gamma ray which is a type of electromagnet wave
205
what is the nature of a alpha particle
highly ionising
low penetration -> stopped by paper or a few cm of air
2+
206
what is the nature of a beta particle
medium ionising
medium penetration -> stopped by a few mm of aluminum + a few meters of air
1-
207
what is the nature of a gamma ray
low ionising
high penetration -> stopped by a few mm of lead
208
practical: investigate the penetration powers of different types of radiation using radioactive souces
Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a one minute period
Repeat this three times, and take an average
Now place a radioactive source a fixed distance of 3 cm away from the tube and take another reading over a one minute interval
Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
Repeat the above experiment for other radioactive sources
analysis of results
if the count over that interval falls to background levels (allow for a little random variation), then the radiation has all been absorbed
Note that some sources will emit more than one type of radiation
If the radiation is stopped by paper, the source will be emitting alpha
If the radiation is stopped by a few mm of aluminium (about 5 or 6) then the source is emitting beta
If some radiation is still able to penetrate a few mm of lead (5 or 6) then the source is emitting gamma
209
what happens to the mass number of an atom if it decays by emitting one alpha particle
mass number decreases by 4
atomic number decreases by 2
210
what happens to the mass number of an atom if it decays by emitting one beta particle
mass number stays the same (a neutron turns into proton)
atomic number increases by one
211
what happens to the mass number of an atom if it decays by emitting a gamma ray
mass number stays the same
atomic number stays the same
212
what happens to the mass number of an atom if it decays by emitting one neutron
mass number decreases by 1
atomic number stays the same
213
what can detect ionising radiation
geiger-muller detector
photographic film
214
what are the backround causes of radiation
radon gas - 50% - natural
rocks and building materials - 15% - natural
medical (xrays...) - 13% - man
food - 11% - natural
cosmic rays - 10% - medical
215
does radioactivity decrease over time
yes
216
what is radioactivity measured in
becquerel
217
what does half life mean
The time taken for half of nuclei of a radioactive source to decay
218
is the half life of every element the same
no
219
uses of radioactivity in industry
sterilizing food
determining the age of ancient artefacts
checking the thickness of materials
smoke alarms
220
uses of radioactivity in medicine
sterilising medical equipment
Diagnosis and Treatment of Cancer
221
what is the difference between contamination and irradiation
Contamination is when the radioactive substance itself gets on or in you, and that does make you radioactive
irradiation is:
The process of exposing a material to ionising radiation
Irradiating a substance does not make it radioactive
222
what are the dangers of ionising radiations
can cause mutations in living organisms - ratiation enters nucleus of cell and destroys DNA and when it reforms it may mutate
can cause damage to cells and tissue
the problens arising from the disposal of radioactive waste and how these risks can be reduced (bury the radioactive material however some of them have long half lives
223
what can nucleur reactions (fusion, fission, radioactive decay) be a source of
energy
224
how can uranium 235 be split
by fission
a neutron is fired at the U235 nucleus which makes it unstable
the nucleus splits (fission)
energy is released as kinetic energy of the fission products
225
what is uranium 235 split into
2 smaller radioactive daughter nuclei (not always identical)
a few neutrons
energy
the combined mass of the 2 daughter nuclei equal the parents
226
how can a chain reaction be set up with U235
Only one extra neutron is required to induce a uranium-235 nucleus to split by fission
so one neutron is fired at the U235 nucleus which then splits into two daughter nuclei which decay and produce more neutrons
During the fission, it produces two or three neutrons which move away at high speed
Each of these new neutrons hits a different U235 nuclues which starts another fission reaction, which again creates further excess neutrons
227
what is a chain reaction
a sequence of reactions where a reactive product or by-product causes additional reactions to take place
228
what is a control rod
absorb excess neutrons which increase or decrease the rate of fission
control rods can be moved in and out of the reacter
229
what is a moderator
slows down high speed neutrons
which increases the rate of reaction and making it more efficient
230
what is the purpose of shielding
The purpose of shielding is to absorb hazardous radiation
The daughter nuclei formed during fission, and the neutrons emitted, are radioactive
The reactor is surrounded by a steel and concrete wall that can be nearly 2 metres thick
This absorbs the emissions from the reactions
It ensures that the environment around the reactor is safe
231
what is the difference between fission and fusion
fission splits a larger nucleus into 2 smaller ones and releasing neutrons
can happen at low temperatures and pressures
fusion is 2 smaller nuclei combining into one larger one
cannot happen at low temperatures and pressures
very difficult to make a practical fusion station
232
what is fusion
2 smaller nuclei joined to form a larger one
this larger one is not as big as the total mass of the 2 smaller nuclei as the missing mass is given off as energy
233
what produces energy for stars
fusion
234
what conditions are needed for nuclear fusion
high temperatures
high pressures
high kinetic energy
these are needed to overcome the electrostatic repulsion of the 2 nuclei
235
what does N/Kg measure
gravitational field strength
236
what is the universe
a large collection of billions of galaxies
237
what is a galaxy
large collection of billions of stars
238
what galaxy is our solar system in
Milky way
239
why does gravitational field strength vary from planet to planet and moon to earth
the different masses and radiuses
240
what does gravitational force cause
causes moons to orbit planets
causes the planets to orbit the Sun
causes artificial satellites to orbit the Earth
causes comets to orbit the Sun
241
what are the differences in the orbits of comets, moons and planets
planets have a slightly elliptical orbit around the sun
moons orbit planets in circles
comits orbit the sun in a very elliptical orbit
242
what is the orbital speed formula
(2 x pi x orbital radius) / time period
243
how can stars be classifed by colour
Warm objects emit infrared and extremely hot objects emit visible light as well
Therefore, the colour they emit depends on how hot they are
A star's colour is related to its surface temperature
A red star is the coolest (at around 3000 K)
A blue star is the hottest (at around 30 000 K)
244
what does the stars color relate to
surface temperature
245
evolution of stars of similar mass to the sun
stellar nebula (cloud of gas + dust)
gravity pulls the cloud inwards, causing it to shrink and heat up forming a protostar
protostar
eventually the core of the protostar gets hot enough for fusion to start becoming a main sequence
main sequence star (fuses hydrogen into helium in its core)
eventually the star runs out of fuel in the core for fusion and the core shrinks as fusion stops pushing outwards
as the core shrinks, fusion begins in a layer around the core and the star swells up to become a red giant
red giant star
once the helium fusion has finished, the star collapses and becomes a white dwarf which cools over time
white dwarf
nebula
246
evolution of stars with a larger mass than the sun
stellar nebula (cloud of gas + dust)
gravity pulls the cloud inwards, causing it to shrink and heat up forming a protostar
protostar
eventually the core of the protostar gets hot enough for fusion to start becoming a main sequence
main sequence star (fuses hydrogen into helium in its core)
eventually the star runs out of fuel in the core for fusion and the core shrinks as fusion stops pushing outwards
as the core shrinks, fusion begins in a layer around the core and the star swells up to become a red super giant
red super giant star (the larger stars become a red super giant quicker than the smaller ones)
once the helium fusion has finished the core of the star will suddenly collapse which is a supernova
supernova
at the center of the explosion, a dense body called a neutron star will form
neutron star
the outer remnants of the star are ejected into space forming new nebulas
in the most massive stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole
247
materials used for moderator
graphite
water
248
materials used for control rod
boron
