Physics Paper 2 Flashcards
1
Q
what is a moment?
1 mark
A
- forces cause objects to rotate
- the turning force is called a moment
1
Q
how do you work out a moment of force?
1 mark
A
- force x distance
- Nm = N x m
2
Q
how would you get the max moment?
1 mark
A
- push at right angles to maximes the distance
- (normal to the direction of the force)
3
Q
how do gears fit to transmit a turning effect?
3 marks
what direction? what makes it bigger?
A
- their teeth interlock so if it turns the other will turn in the opposite direction
- a force applied to a bigger moment will be larger as its further from the pivot
- the larger the gear the slower it will spin
4
Q
how do you work out how speeds and moments change?
3 marks
gears
A
- gear ratio
- if a gear has 10 teeth and another has 5 it will be 2:1
- this means every 1 turn of the larger will turn the smaller one twice
5
Q
why does resistance increase with temperature?
5 marks
A
- work has to be done against resistance causing a electrical transfer of energy
- some is put to thermal heating up resistor
- this is because electrons colide with ions giving energy -> vibrate-> heat
- the more vibrations the higher the resistance
- however thermistors decrease resistance the higher the temperature
6
Q
practical
how to use a circuit to investigate a filament lamp?
6 marks
also could be about a fixed resistor
A
- connect a series circuit (lamp,volt meter in parallel, ampmeter in series and a cell)
- change potential diffrence altering curent
- take readings of ampmeter and voltmeter to see how the current varies
- plot current against potential diffrence
- use data to work out resistance for each measurment to see the resistance changing
- make sure it doesnt get too hot and repeat for mean
7
Q
how do you investigate a diode?
2 marks
A
- take measurements with a range of currents
- swap diodes direction and find that the current wont be able to flow
8
Q
how can you investigate a Thermistors?
2 marks
heat dependant resistor
A
- keep a constant potential difference and gradually heat thermistor
- you should see as temp increases current through thermistor increases as the resistances decreases
9
Q
how do you investigate LDRs?
3 marks
light depentant resistor
A
- go in a dim room
- keep potential difference constant and slowly adjust the light level near LDR
- you should see as it gets brighter the current increases and resistance decreases
10
Q
how does adding a resistor in parallel reduce total resistance?
3 marks
A
- in parallel both resistors have the same potential difference
- but by adding another loop the current has more than one direction to go in
- this increases the total current that can flow decreasing the resistance
11
Q
practical
how could you use a circuit to investigate properties
a long 4 marks :)
of resistor and filament lamp
A
- vary the output potential difference and record reading (ammeter and voltmeter) from the series circuit
- replace the resistor with a filament lamp and repeat
- now connect a second filament lamp in parallel to the first and connect ammeters (1 in the second parallel and one by cell) and a second voltmeter with the second filament lamp
- again vary potential difference and write down the current through each ammeter and p.d across each component
page 76 for the picture
12
Q
what should you see when you investigate properties of circuits?
3 marks
of the resistor and filament lamp
A
- for the series circuit as p.d increases the current through the resistor increases
- similar but non-linear when using a filament lamp instead of a resistor
- the same happens in a parallel but the overall current is higher and the resistance is lower
13
Q
how do fuses protect circuits?
1 mark
A
- they melt and break the circuit if the current gets too high
14
Q
how is the heating of a circuit good?
3 marks
A
- toasters contain a coil of wire with a high resistance that increases temp(so much it glows)
- this gives off infrared radiation cooking the food
- filament bulbs and electric heaters work the same way
15
Q
what is the unit of power?
1 mark
A
watts
16
Q
what is power?
1 mark
A
amount of energy transfered per second
17
Q
what is a power rating used for?
3 marks
A
- in microwaves the higher the power the faster it will take to cook
- customers can see the lower the power the cheaper it is to run as it uses less electric
- however its not always the case as it doesn’t show the efficiency
18
Q
What does electrical power depend on?
2 marks
A
- Current
- Potential difference
19
Q
What is a alternating current / whats it produced by?
4 marks
whats whe voltage and frequency of it in the mains
A
- movement of charges that is constantly changing direction
- prodused by Alternating voltages
- Uk mains supply -> 230V
- frequencey = 50Hz
20
Q
what is direct current and hows it produced?
2 marks
A
- produced by cells in direct voltage
- one direction
21
Q
what are the 3 separate wires in most cables?
3 marks
A
- live wire
- neutral wire
- earth wire
22
Q
what is the live wire?
2 marks
A
- brown
- carries the 230V
23
Q
what is the neutral wire?
3 marks
A
- blue
- 0V
- completes circuit
24
what is the earth wire?
| 4 marks
- green and yellow
- protects wiring
- carries current away if it goes wrong
- 0V
25
how do you get an electric shock?
| 4 marks
- body is 0V
- if you took live wire a large p.d produces a current through the body
- this causes electric shock
- even if the plug is off there is still a p.d even tho there is no current
26
what is a surge and what could it cause?
| 2 mark
- sudden increase in current due to a change in a circuit
- it can cause fires and electric shocks
27
how is a surge prevented?
| 4 marks
- if live wire touches the metal case and the current gets too high the fuse will melt which breaks the circuit preventing shock and fire as it isolates the appliance
- the fuse should be rated just above the normal current
- the larger the current the thicker the cable as it stops it from getting too hot
28
what are circuit breakers?
| 4 marks
## Footnote
compared to a fuse
- instead of a fuse a large current may turn off a circuit breaker
- this is faster than a fuse melting
- they can be reset so it's easier than having to replace a fuse
- more expensive than a fuse
29
what is double insulation?
| 3 marks
- when there is no metal showing as it's in a plastic coat
- they only carry live and neutral wires (two-core cables)
- they don't need an earth wire
30
what is the build up of static caused by and how?
| 4 marks
- when insulating materials are rubbed together
- negatively charged ions will be scraped off one and dumped on the other
- in insulators, electrons aren't free to move
- this build-up of charge is static electricity with positive static on the one that lost electrons and equal negative on the other insulator
31
how can electrically charged objects attract uncharged objects?
| 4 marks
- charges on a surface can move a little
- negative charges from a surface(like a balloon) repel the negative charges on another surface
- this leaves positive charges to go to the front of the surface which will then attract the wall and balloon together
- this is called attraction by induction
32
how can too much static cause a spark?
| 2 marks
- potential difference between object and earth increases
- when large enough electrons can jump across the gap between the object and the earth -> spark
33
what are 4 uses of electrostratic sprayers?
| 4 marks
- Copying images on a photocopier
- Reducing dust and smoke in industrial chimneys
- Insecticide sprayers
- Paint sprayers
34
How do paint sprayers work?
| 5 marks
- Used on bikes and cars
- Spray gun charges up small drops of paint
- Each drop will repel as they have the same charge giving a fine spray
- The object being painted is given an opposite charge to the gun to attract the paint
- This gives an even paint without wasting
35
How does insecticide sprayers work?
| 4 marks
- Used on crops
- Spray charges up small drops
- Each drop will repel as they have the same charge giving a fine spray
- plants are charged by induction
36
how is refueling vehicles dangerous?
| 2 marks
## Footnote
in terms of static
- Static can build up as fuel flows in
- This can lead to a spark Which can cause an explosion in dusty or flumey places
37
what is the problem with static on planes and how does it occur?
| 2 marks
- Friction between air and the plane causes it to become charged
- This can interfere with communication equipment
38
how does lighting work?
| 3 marks
- Raindrops and ice bump into each other inside storm clouds
- Leaving the top of the cloud positive While the bottom is negative
- This creates a huge voltage and a big spark, which can damage homes and start fires
39
How can objects be earthed to stop electrostatic charge building up?
| 4 marks
- Sparks can be prevented by connecting a charged object to the ground using a conductor (this is called earthing)
- It provides an easy route for the Electrostatic charges to travel stopping build-up of charge
- Electrons flow down if negative and up if positively charged
- Fuel tankers must be earthed to prevent sparks leading to explosions
40
what feild do you get when 2 oppositely charged parallel plates face?
| 1 mark
uniform field
41
explain how can sparking be explained by electric feilds?
| 6 marks
- When an object becomes statically charged it generates its own electric field
- Sparks are caused when there's a high enough potential difference between charged objects and the Earth.
- Because this causes a strong electric field between the charged objects and the Earthed object.
- strong feild causes electrons in the air to be removed
- When air is ionised, it's much more conductive, so a current can flow through it
- making a spark
42
what happends when you put a compass by a magnet and what does it allow you to do?
| 2 marks
- it will line up with the magnetic field
- this allows you to move the compass around and draw in the fields with the arrows
43
what is an induced magnet?
| 2 marks
- a temporary magnet
- the magnet is only made when it's in another field
44
what is the relation between how quickly an object stop producing a feild and the maturial?
| 2 mark
- the softer it is the faster(iron/nickel)
- hard material is the slowest and the hardest ones and the permanent magnets
45
explain what are all the uses of magnetic maturial?
| 7 marks
- fridge doors -> permanent magnet to keep the fridge closed
- cranes -> induced electromagnets to move magnetic material
- doorbells -> Electomagnets turn on and off rapidly to release an arm that strikes a metal bell
- magnetic separators -> separate metal items
- maglev trains -> slightly float to reduce friction
- MRI machines -> use magnetic fields to make images of the body without ionising radiation
- speakers/microphones (page 90)
46
how do you use you hand to work out direction that the field curves?
| 4 marks
- right hand
- thumb up which will be the direction of the current
- close your fist so the direction that your fingers are pointing is direction of field
- (anticlockwise or clockwise)
47
how do you work out the dirction of motion (resulting force) of curent and a magenetic field?
| 5 marks
- left hand
- put your hand in position with each 90 degrees from the other
- thumb -> motion
- pointy finger -> direction field is going
- middle -> current
48
what is magentic flux density?
| 2 marks
- how many field lines in a region
- it shows strength of felid
49
how does a coil of wire with a curent rotate in a magnetic feild?
| 3 marks
- moter
- forces act on 2 side arms of the coil of the wire carrying the current
- these forces act in opposite directions so the coil rotates
50
what does the spilt-ring commutator do to rotate a magnetic feild?
| 1 mark
- it swaps the contact every half-turn to keep it rotating in the same direction
51
how can the moter be reversed?
| 2 marks
- swapping polarity of d.c. supply
- or swapping magnetic poles
52
what is a solenoid?
| 2 marks
- a long coil of wire (loops)
- electromagnet that can turn on and off using current
## Footnote
page 88
53
how can you increase strength of magnetic felid?
## Footnote
made by a wire
- wrapping it into a long coil of loops (solenoid)
54
what happends when feild lines around each seperate loop of wire lines up?
| 5 marks
## Footnote
basically what does the feild look like in a solenoid
- inside the solenoid, you get lots of field lines pointing in the same direction
- the field is strong and almost uniform
- outside the overlapping field lines cancel each other out
- so at the ends of the solenoid they are weak
- you end up with the same field lines as a bar magnet
## Footnote
p88
55
how can you increase feild strengh of solonoid?
| 2 marks
- increase curent
- put iron in the center as it becomes and indused magnet
56
what is electromagnet induction?
| 1 mark
- the induction of potential difference (and current of its a complete circuit) in a wire which is experiencing a change in magnetic feild
57
how can you get a electromagnetic induction through electrical conductors and magnetic feilds?
| 3 marks
- Rotating a magnet or a coil of wire or a conductor In a magnetic field
- If you rotate the magnet in opposite directions, then the potential difference and current will be reversed (likewise if you Reverse polarity)
- If you keep a coil moving back and forth or keep rotating in the same direction, you will produce an alternating current.
58
how can you increase the size of induced p.d?
| 3 marks
- increasing the strength of the magnet
- increase the speed of changing field
- more turns per unit length on the coil
59
how does induced current/p.d oppses the change it makes?
| 1 mark
- using a magnetic field to return things to the way they were
60
how do transformers work?
| 6 marks
- using induction to change the size of the potential diffrence of an alternation current
- two coils joined with an iron core
- when alternating p.d is applied to primary coil it makes a alternating magnetic feild
- iron core is magnetised and demagnetised
- changing field induces a p.d on the second coil
- this is almost 100% efficient
61
what is the diffrence between a step-up and a step-down transformer?
| 4 marks
step up:
- increases p.d in the second coil
- more turns on the second coil
step down:
- decreases p.d
- less turns on secondary
62
what is a dynamo?
| 2 marks
- direct current generator
- uses a split-ring communicator to swap connections every half turn to keep current flowing in the same direction
63
what does a genorater do?
| 2 marks
- applys a force to rotate a coil in a magnetic field
- as the coil/magnet spins a current is induced in coil changing current every half turn
64
how are alternators diffrent from dynamos?
| 2 marks
- instead of a split ring they use a slip ring and brushes so the contacts dont swap every half-turn
- this produces an alternating p.d and current if it forms a complete circuit
65
how do microphones work?
| 6 marks
- electromagnetic induction
- sound waves hit a flexible diaphragm that is attached to coil
- coil surrounds the pole of a permanent magnet and is surrounded by other pole
- this means the diaphragm and coil move generating a current in coil
- the movement of the coil depends on the properties of the wave
- (the louder the further the diaphragm moves)
- this is how microphones convert the pressure of vibrations into current
66
how do loud speakers work?
| 3 marks
- coil Is wrapped around one pole of a permanent magnet causing a force to move a cone
- When the current is reversed, the force acts in the opposite direction
- Movements make the cone vibrate, which makes the air around the cone vibrate making pressure that causes a sound wave.
67
how do power stations use turbines to turn a huge alternator?
| 5 marks
- fuels are burned to heat water converting it to steam - turning a turbine
- turbine is connected to a magnet in a generator
- as the turbine spins the magnet does as well inducing a large p.d and alternating current in coils
- coils join in parrel to produce a single output
- this is similar to hydroelectric, tidal and wind power but you dont have to heat anything to spin the turbine
68
# practical
how can you find the dencity of a object?
| 8 marks
- measure mass using electronic balance
- fill a bottle with a known Density liquid
- place the stopper in the bottle
- measure the mass of the bottle
- empty the bottle and put the object in, then fill it back up before puting stopper back on
- do the mass of the liquid - ( mass of liquid with object - mass of object) to get mass of displaced water
- do that mass/density to get the volume of that object
- mass of object/volume = density
68
how would you find the dencity of a liquid?
| 4 marks
- use an electronic balance to measure the mass of the measuring cylinder
- pour liquid in and find the new mass to work out the change
- find the volume of the liquid by looking at the scale
- mass/volume = density
68
how do transformers in the national grid work?
| 5 marks
- after electric is generated it goes through a net of wires and transformers that conect power to the consumer(national grid)
- it needs to transfer a large amount of power so it needs to have a high p.d or current
- it can't have a high current tho due to it heating up wire and losing efficiency
- so they need high voltage and low resistance cables and transformers
- step-up transformers are used (400,000V) to keep the current low then step-down transformers are used close to the consumer so make it safe
69
how does specific heat capacity relate temperature and energy?
| 5 marks
- heating increases thermal energy
- this means the temperature is a way of measuring "internal energy"
- but it takes more energy to increase the temp of some materials than others
- materials that need to gain lots of energy to warm up also release loads when they cool
- change in energy stored when you heat is related to the temperature by its specific heat capacity
70
what is specific heat capacity?
| 1 mark
- the change in energy in a substance thermal store needed to raise the temp of 1Kg of that substance by 1 degree
71
# practical
how can you find the specific heat capacity of water?
| 7 marks
- use an electronic balance to measure the mass of the insulating container
- fill the container with water and measure mass again to find the difference in masses which is the mass of water in the container
- set up a joulemeter on 0 connecting it to an electric immersion heater in the container and put a lid on the container
- measure temp of the water and then turn on the power
- when it's increased by 10 degrees stop the experiment and record energy on joulmeter and increase in temp
- change in thermal energy / (mass x change in temp)
- repeat for an average
72
# practical
how can you test to see that temp doesn't decrease/increase(depending if you are melting or freezing) untill it changes state?
| 6 marks
- fill a beaker with crushed ice
- place the thermometer in and record temp of ice
- using a Bunsen burner heat
- at regular intervals record temp and state of ice
- continue until it begins to boil
- plot a graph of temp against time
## Footnote
p96 for graph
73
what is specific latent heat?
| 1 mark
- energy needed to change the state of 1Kg of that substance without changing the temp
74
# how are this diffrent?
1. specific latent heat of fusion
2. specific latent heat of vaporisation
| 2 marks
1. between solids and liquids (melting/freezing)
2. between liquids and gases (evaporating/condensing)
75
what is kelvin?
| 2 maarks
- negative 273 degrees
- the coldest anything can be to where particles are basically still
76
what happens when a container doesnt have a fixed volume?
| 2 marks
## Footnote
like a balloon
- the volume becomes consistent where the pressure inside pushing out = pressure outside pushing in
- you can change vol by changing the pressure on the inside or outside
77
how can you change the pressure of a gas inside a container?
| 3 marks
- heating/cooling
- as e.g. a balloon is heated particles inside gain kinetic energy increasing pressure
- then to outwards pressure would be higher than surrounding pressure causing the balloon to expand
- cooling has the opposite effect
78
how can you increase the external pressure on a gas?
| 3 marks
## Footnote
in an air tight syring and the atmosphere
- push down on the plunger increases inward pressure so the inward pressure is larger than the outward
- this causes compression
- as you increase altitude the atmospheric pressure decreases rising container of gas as it expands due to a decrease in inward pressure
79
what does doing work on a gas do?
| 1 mark
increases temp
80
what does it mean for something to be (in)elastically distorted?
| 3 marks
- inelastically distorted = object can't go back to its original shape/length after a force was applied
- when the object is stretched or compressed **some** energy is transferred to the elastic potential energy store
- if that object is elastically distorted **ALL** energy is transferred to elastic potential
81
what is elastic limit?
| 1 mark
- the point at which an object stops distorting elastically and begins to distort inelastically
82
what is extention directly proportional to?
| 2 marks
- force
- the constant depends on the material (the stiffer the bigger) :)
83
when does extention stop being propotional to force?
| 1 mark
- after the elastic limit when the object becomes permanently stretched
84
how could you find what masses to uses when investigating the link between force and extention?
| 3 marks
- pilot experiment
- using an identical spring to the one you will be testing load it with masses one at a time and record the force and extension each time
- plot a force-extension graph and check you get a straight line otherwise if its curved you will have to use lighter weights
85
# practical
how can you investigate the link between force and extention?
| 5 marks
- measure the natural length of the spring (no load) with an mm ruler and add a marker to the top and bottom of the spring
- add mass to the spring and allow spring to reset to the new length
- the extension is the change in length
- repeat process until you have enough measurements
- plot a force-extension graph until it exceeds the limit of proportionality
86
what should you see when you investigate the link between force and extention?
| 3 marks
- The larger the force the larger the extension
- force = gravitational force
- area under linear part of graph = work done
87
what is fluid pressure?
| 3 marks
- pressure caused by collisions of gas/liquid on a surface
- it always exerts force at right angles
- depends on the area of fluid it is in contact with
88
what does fluid pressure depend on?
| 1 mark
- depth
- density
- gravitational field strengh
89
describe how objects in fluids experience upthrust
| 4 marks
- when an object is in a fluid the pressure of the fluid exerts a force in every direction
- pressure increases with depth so the force at the bottom of the object is larger then the top
- this causes a resultant force called upthrust
- upthrust = weight of fluid displaced
90
when do objects float and when do they sink?
| 5 marks
- if upthrust = objects weight it will float otherwise it wont
- this means it depends on the density
- if an object is less dense than the fluid it displaces it will become equal to the upthurst so it will float
- otherwise, it will sink as weight will always be large then upthrust
- the less dense it is the higher up it will float
91
what happens to atmospheric pressure when you go up and why?
| 3 marks
- it decreases
- on a graph, it is curved as pressure is affected by density which varies with height
- as altitude increases there are fewer air molecules to collide with
92
how is atmospheric pressure created?
| 1 marks
- on a surface by air molecules colliding with the surface
