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Physics paper 2 Flashcards

1
Q

what is a system

A

a single object or group of objects that your interested in

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2
Q

what happens when a system changes

A

energy is transferred into or away from the system, between different objects in the system or between different types of energy stores

some energy is dissipated and stored in less useful ways

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3
Q

what is a closed system

A

the net change in energy is zero

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4
Q

define work done

A

the energy transferred by a force acting over a distance

the force does work to move the object and energy is transferred mechanically from one store to another

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5
Q

when energy is wasted what can you still say

A

work has been done

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6
Q

what is the equation for work done

A

E = f x d
work done = force distance
(J) = (N) x (m)

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7
Q

what does a force doing work often cause

A

a rise in temperature as energy is dissipated to the thermal stores of the moving object and its surroundings. this means that the process is wasteful and the efficiency of the process in reduced

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8
Q

what is the equation for efficiency

A

useful / total

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9
Q

what happens when you push something along a rough surface

A

you are doing work against frictional forces
energy is been transferred to the kinetic energy store of the object because it starts moving but some is also being transferred to the thermal energy stores due to friction
this causes the overall temperature of the object to increase

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10
Q

what is power

A

the rate of energy transfer (how much work is been done every second)

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11
Q

what is power measured in

A

watts

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12
Q

what is the formula for power

A

work done / time taken

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13
Q

what is force

A

a push or a pull on an object that is caused by it interacting with something

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14
Q

what are non-contact forces caused by

A

interacting fields

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15
Q

what are contact forces caused by

A

friction

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16
Q

why is there a gravitational attraction between the Earth and the Sun

A

because their gravitational fields are interacting

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17
Q

what can interacting magnetic fields cause

A

attraction or repulsion between magnetic objects

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18
Q

what does interaction between electric fields cause

A

attraction or repulsion between electrical charges

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19
Q

what is Newtons third law

A

whenever two object interact both objects feel an equal but opposite force - an interaction pair

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20
Q

what does a free body force diagram show

A

an isolated body and all the forces acting on it

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21
Q

what do objects in equilibrium have

A

a resultant force of zero

either stationary or moving at a steady speed

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22
Q

what is moment

A

a force, or several forces can cause an object to rotate, the turning effect of a force is called its moment

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23
Q

what is the equation for the moment of a force

A

force x distance

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24
Q

when will a current only flow through an electrical component

A

a current will only flow through an electrical component if there is a potential difference across that component and if the circuit is closed/complete

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25
the higher the potential difference across a given component
the higher the current will be
26
calculate charge
current x time
27
how would you investigate the relationship between current, pd and a chosen component
the standard test circuit - set up circuit with d.c source, voltmeter, ammeter and component of choice - change the output pd of the power supply - this alters current flowing through the circuit and the pd across the component - take several pairs of readings from the ammeter and voltmeter to see how the current through the component varies as the pd across it changes - plot current against pd to get current, pd graphs - use data to work out resistance for each measurement - you can see how resistance changes as I and V change don't let circuit get too hot or readings will mess up disconnect between readings to cool down repeat work out means
28
how can you investigate thermistors
keep the pd supply constant and gradually heat the thermistor place thermistor is beaker of hot water as temperature increases, current in thermistor increases and resistance decreases
29
how can you investigate LDR's
conduct in a dim room keep pd constant and slowly adjust the light level near to LDR using lam with dimmer switch light level gets brighter, current through LDR increases and resistance decreases
30
what is current and pd like in a series circuit
current is the same everywhere | pd is shared between components
31
what is current and pd like in a parallel circuit
current is shared between the branches - total current flowing around the circuit is equal to the total of all the currents through sperate components pd is the same across all components
32
what happens if you add two resistors in a series circuit
the total resistance of the two components is just the sum of the resistances because they have to share the total potential difference. The bigger a components resistance, the bigger its share of the total potential difference
33
what happens if you add two resistors in a parallel circuit
if you have two resistors in a parallel circuit their total resistance is less than the resistance of the smallest of the two resistors - in parallel both resistors have the same pd across them as the source - this means the pushing force making the current flow is the same for each resistor you add - but by adding another loop the current has more than one direction to go in - this increases the total current that can flow around the circuit - using V=IR an increase in current means a decrease in the total resistance of the circuit
34
what does the power transferred by an appliance depend on
potential difference and the current flowing through it
35
what is the neutral wire
blue completes the circuit electricity flows out through the blue wire which is always at 0V
36
what is the live wire
red or brown | carries the voltage at 230V
37
what is the earth wire
green and yellow for safety and protecting the wiring it carries the current away if something goes wrong and stops the appliance becoming live always at 0V
38
why does touching the live wire give you an electric shock
your body is at 0V so when you touch it a large pd is produced across your body and current flows through you
39
what would happen if you made contact with the live wire in a plug socket that is turned off
still a danger of an electric shock a current isn't flowing but there is still a pd in the live wire if you made contact with the live wire your body would provide a link between the supply and the earth so current would flow through you
40
give one advantage and disadvantage of using circuit breakers instead of fuses
- they turn off quicker than a fuse melting - they can be reset instead of replaced - but more expensive
41
when do you not need an earth wire
when an appliance is double insulated
42
the changing direction of the current...………….
changes the direction of the magnetic field
43
what happens when a current, carrying conductor ( a wire) is put between magnetic poles
the two magnetic fields interact and the result is a force on the wire
44
how can you find the size of the force acting on a conductor in a magnetic field
``` F = B x I x L force = magnetic flux density x current x length of wire (N) = (T) x (A) x (m) ```
45
how is a build up of static caused by friction
- when insulating materials are rubbed together electrons will be transferred from one material to the other - as the materials are insulators these electrons are not free to move and this build up of charge is called static electricity - the materials become electrically charged with a + static charge on one that has lost electrons and an equal - charge on the other
46
which becomes negatively charged out of a polythene rod and an acetate rod
``` acetate = + polythene = - ```
47
electrically charged objects...…………..
exert a force on each other
48
how can you see the forces between two electrically charged objects
suspend a rod with a known charge from a piece of string so its free to move and place charged objects next to it to see repulsion and attraction
49
what happens if you run a comb through your hair
electrons will be transferred to the comb making it negatively charged. It can then be used to pick up little pieces of uncharged paper - holding it near the little pieces of paper causes induction in the paper which means they jump and stick to the rod
50
how does to much static cause a spark
- as electric charge builds on an object, pd between earth and object which is 0V increases - if the pd gap gets large enough electrons can jump across the gap between the charged object and the earth - this is the spark - they can also jump to any earthed conductor that is near by which is why you can get static shocks from clothes or getting out of a car - usually happens when the gap is fairly small but lightning is just a massive phat spark
51
how do photocopiers use static electricity
copy images onto a charged plate before printing them
52
how can static electricity in industrial chimneys be used
to reduce the dust and smoke that rises
53
why is there a static danger when refuelling cars
as fuel flows out of a filler pipe then static can build up which can lead to a spark causing an explosion in dusty or fumy places like petrol stations
54
why is there a static danger when on airplanes
as planes fly through the air friction between the air and the plane causes the plane to become charged this build of charge can interfere with communication equipment
55
why is there a static danger in lightning
raindrops and ice bump together inside storm clouds leaving the top of the cloud positively charged and the bottom of the cloud negatively charged. This creates a huge voltage and a big spark which can damage homes or start fires when it strikes the ground
56
how can you stop electrostatic charge building up
- dangerous sparks can be prevented by connecting a charged object to the ground using a conductor (earthing) - earthing provides an easy route for the static charges to travel into the ground - this means no charge build up to give you a shock or make a spark - the electrons flow down the conductor to the ground if the charge is negative and flow up the conductor from the ground if the charge is positive - fuel tankers must be earthed to prevent any sparks that might cause the fuel to explode
57
discuss electric field lines
- always at right angles to the surface - positive to negative - closer together the lines are the stronger the field is, the further you go from a charge, the weaker the field is so the lines are further apart - it is the region around a charged object where if a second charged object was placed inside it, a force would be exerted on both the objects
58
how can sparking be explained by electric fields
when an object becomes statically charges it develops an electric field interactions between this field and other objects are the cause of events like sparking sparks are caused when there is enough pd between a charged object and the earthed object a high pd causes a strong electrostatic field between the charged and earthed object strong field causes electrons in the air particles to be removed (ionisation) air is normally an insulator but when it is ionised it is much more conductive so a current can flow through it - the spark
59
why is steel magnetic
because it contains iron
60
what do permanent magnets always do
produce their own magnetic field
61
what does magnetically soft mean
it will lose its magnetism quickly - pure iorn - nickel iron alloys
62
what happens when current flows through a long straight conductor
a magnetic field is created around it
63
what happens when a current carrying conductor is placed between two magnetic poles
a force is exerted on the wire to experience the full force the wire has to be at 90 degrees to the magnetic field if the wire runs along the field it won't feel any force at all the changing direction of the magnetic field or current will change the direction of the force because the force always acts in the same direction relative to the magnetic field and direction of the current

Science (7 decks)

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