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FULL LAST MIN Flashcards

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1
Q

How can energy of a system be changed

A

Mechanically (forces doing work), Electrically (by moving charge doing work), by heating or by radiation

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2
Q

What does power mean

A

How much work is done per second

-It is the rate of energy transfer and is measured in Watts

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3
Q

How do you work out power

A

work done/ time taken

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4
Q

Whats is the effect of a gravitational field on objects

A

non contact force- the gravittional attraction between objects is caused by their gravitational fields interacting

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5
Q

What is the effect of magnetic fields on objects

and electrostatic force

A

interacting magnetic fields cause attraction and repulsion between magnetic objects
-electrostatic force causes attraction and repulsion between electrical charges and their electric field

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6
Q

What are the forces that occur when objects are in contact with each other

A

both objects feel an equal and opposite force called an interaction pair (3rd law)
-these pairs can be shows with vectors (arrows diagram)

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7
Q

Objects in equilibrium have a resultant force of…..

A

zero (this can be stationary or moving at constant speed)

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8
Q

Describe a situation where energy is transferred Mechanically (by doing work)

A

if a box is lifted off the floor work is done against gravity which causes energy to be transferred mechanically to objects kinetic and GPE stores

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9
Q

Describe a situation where energy is transferred electrially

A

electric ions carry charge electrically from mains power supply to thermal energy store of metal plates

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10
Q

What is a moment

A

The turning effect of a force

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11
Q

How do you calculate a moment

A

force x distance

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12
Q

How would someone get the maximum moment/turning effect

A

you could push at right angles as any other angle means smaller distance so smaller moment

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13
Q

What is the principle of moments for a an object in equilibrium

A

Sum of clockwise moments is = sum of the anticlockwise moments

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14
Q

What do leavers do

A

They make it easier to do work by transferring the turning effect by increasing the distance from the pivot where a force is applied

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15
Q

Explain how gears transmit rotational effects of forces

A

They fit together to transmit turning effects by interlocking,
a larger gear is slower but creates a large moment
a small gear is faster but has smaller moment

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16
Q

What is meant by potential difference

A

driving force which pushes the charge around

higher the PT the higher the current

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17
Q

What is the current

A

Flow of electric charge (electrons) around a circuit and it will only flow if theres a potential difference

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18
Q

What is resistance

A

anything that slows the flow down

usually increases with temperature

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19
Q

How do you measure charge

A

current x time

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20
Q

What is charge

A

current is the rate of flow of charge.

its a flow of electrons

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21
Q

Describe the current and potential difference in a series circuit

A

Current is the same everywhere

PT is shared between each component

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22
Q

How does the Resistance change in a series in you add a resistor

A

It increases

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23
Q

Why does resistance increase with temperature

A

because the electrical charge has to do work against the resistance
as the current flows through a resister it heats up because the electrons are colliding with ions in the lattice resistor
-If resistor too hot no current will flow (unless thermistor)

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24
Q

How could you investigate a component in series

A

-connect a voltmeter in parallel with the component you’re investigating and ammeter in series
-change the potential difference on power supply and take several readings from the ammeter and voltmeter
for different output voltages
-Plot I-V graph to work out resistance
(make sure circuit doesnt overheat)

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25
Q

What would you find if you kept the PT of a thermistor the same but gradually increased the temperature

A

that as the temperature increases the current through the resistor decreases and the resistance decreases

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26
Q

Describe a test for a LDR

A

Carry out in dim room

  • keep PT constant but slowly adjust the light level near the LDR and measure the current through LDR
  • should find as light intensity increases, current increases and resistance decreases
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27
Q

Describe an IV graph for a diode

A

current only flows through a diode in one direction
diodes have high resistance in opposite direction
(so flat line and then sudden increase)

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28
Q

What is a thermistor and what is it used for

A

hot conditions resistance drops
-used in temperature detectors eg) electric kettles
car engines

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29
Q

What is an LDR and name some uses

A

Light dependent resistors

  • in bright light resistance falls so current increases
  • used for automatic night light lights and burgler detectors
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30
Q

How does resistance change in a series and parallel when you add a resistor

A

Series- increases resistance- makes resistors have to share PD

Parallel - decreases total resistance as both resistors have same PD and by adding another loop for resistor you are giving the current another direction so increase in current= decrease in resistance

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31
Q

How can we find the energy transferred in a system with a formula?

A

Current x Potential Difference x time

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32
Q

Explain why the transfer of energy leads to heating

A

Because as energy is transferred some is as thermal energy to thermal stores as heating usually increases resistance. so its dissipated to surroundings

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33
Q

How is efficiency effected by heating

A

it decreases

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34
Q

how do fuses help protect circuits from overheating

A

they melt and break the circuit if it gets too high

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35
Q

Why can a heating effect be useful

A

it toaster a coil of wire has a very high resistance so gives off infrared radiation to bread and cooks it

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36
Q

What is power

A

The rate it transfers energy per second

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37
Q

what can happen to components in a circuit if the temperature increases too high

A

It can cause them to melt and stop working properly

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38
Q

What does a power rating show

A

the maximum safe power an appliance can opperate at

shows the max. energy transferred between store each second

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39
Q

How can you work out electrical power with Potential difference

A

Current x PT

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40
Q

How do you work out Power with Resistance

A

Current^2 x resistance

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41
Q

A mains supply has a……..current

A

an alternating current

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42
Q

A battery supply has a…….current

A

direct current

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43
Q

What is the potential diffence of UK mains power supply

A

230V

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44
Q

How can you turn A.C to D.C

A

using a diode

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45
Q

Describe the neutral wire

A

blue-
completes the circuit
electricity flows out of this wire
has PT of 0Volts

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46
Q

Describe the Live wire

A

brown- carries the Potential difference/voltage

alternates between high positive and negative voltage of 230V

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47
Q

Describe the Earth wire

A

Green and Yellow
it has a PT of 0volts
used for safety and protecting wires
it carries current away to earth if something goes wrong

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48
Q

What is a double insulated appliance

A

doesnt have an earth wire as its already earthed

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49
Q

Why does touching a live wire give you an electric shock

A

Your body is at 0 volts like an earth wire so if you touch a live wire a potential difference is produced across your body and a current flows through you

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50
Q

How could a fire start in a circuit

A

-any connection between a live and neutral wire is dangerous as it creates a low resistance path to earth and huge current so fire could start

51
Q

What do fuses and earthing do

A

Prevent electrical overloads which could start a fire or melt you components or give deadly electric shocks

52
Q

How does a fuse work

A

if a fault develops in live wire, then the current flows through the case and down the earth wire

  • this surge melts the fuse when current exceeds rating and breaks circuit stopping live supply
  • it isolates the whole appliance so you cant get shock
53
Q

What should a fuse rating be

A

near as possible but just higher than the normal operating current
so in event of fault it doesnt overheat and start fire

54
Q

The larger the current the ……the cable needed to carry it

A

thicker

55
Q

What is circuit breaker

some pros and cons too

A

instead of a fuse a circuit breaker trips the circuit so it turns off quicker than the time a fuse would melt
+they can be reset so dont need replacing as much
- but are more expensive

56
Q

What does double insulating materials mean

A

a plastic casing (instead of metal) has no metal parts showing so doesnt need an earth wire

57
Q

how does rubbing an insulator transfer electrons and create a static charge

A

negatively charged electrons are scraped off one material onto another

  • as its an insulator the electrons aren’t free to move
  • this builds up static electricity
  • the material becomes electrically charged with a positive static.
58
Q

Electrically charged particles exert a ……on each other

A

force

59
Q

how do forces of attraction change with distance

A

further means weaker

60
Q

How can an electrically charged object attract uncharged objects (with example)

A

Rubbing a balloon on your head transfers electrons to the balloon leaving it negatively charged
-if you hold the balloon against a wall it will stick because the negatively charges on the wall are repelled and positive charges are attracted to negative balloon

61
Q

How does attraction by induction occur

A

If a negatively charged object is used to charge a neutral object by induction, then the neutral object will create a positive charge.
(The charged object that is brought near will always repel like charges and attract opposite charges.)

62
Q

What is earthing

A

sending current down to the earth

provides easy route for static charge so none builds up

63
Q

How do spark occur

A

If a potential difference is large enough, electrons can jump a gap between charged object and earth making a spark
eg)lightning

64
Q

How do electrostatic sprayers work

A
  • spray gun is charged, so paint droplets become negatively charged
  • object being painted has an opposite charge to attract the fine sprays of paint
  • gives an even coat as areas with paint become negative so theres no build up
  • no paint shadows
65
Q

How does lighting form

A

raindrops and ice bump causing friction and leaves top of cloud positively charged and bottom negative which creates huge voltage and spark which jumps across gap to earth as lightning
-damage homes, start fires

66
Q

How can objects be earthed to stop charge building up

A

by connecting charged object to the ground using conductor through earthing

  • provides easy route for static charge
  • no build up of static so no sparks
67
Q

What do electric charges do

A

Create an electric field around any charged object

stronger as you get closer

68
Q

What happens to a charged object is placed in an electric field? and what is it caused by?

A

it feels a force caused by two charged objects interacting

69
Q

what happens field lines between charged objects point in opposite directions

A

They repel

70
Q

How do you get a uniform field

A

between two positively charged parallel plates

71
Q

How can sparking be explained with electric fields (and therefore static)

A
  • When an object is statically charged it creates its own electric field
  • interactions in this field cause sparking
72
Q

What is ionisation in a electric field

A

Electrons in the air particles to be removed

73
Q

When is air not an insulator

A

when its ionised enough that it becomes more conductive and sparks are made

74
Q

What is a permanent magnet

A

produces its own magentic field

75
Q

What is an induced magnet

A

only produces a field when in another magnetic field

putting any magnetic material into a magnetic field it becomes an induced magnet

76
Q

what does magentically hard mean and give examples

A

lose there magnetism more slowly

permanent magnets are made from magnetically hard materials

77
Q

Name some uses of magnetic fields

A

Doorbells- electromagnets that turn on and off rapidly to repeatedly attract and release an arm which strikes a metal bell

MRI machines- magnetic fields to creat images inside your body without having to use ionsing radiation

78
Q

A moving charge creates a

A

magnetic field

79
Q

explain the right hand rule

A

thumb represents current curled up fingers represent the direction of the magnetic field at right angles to the current

80
Q

in order to experience full force in a motor the wire needs to be at……

A

90 degrees to the magnetic field

if it runs along field it wont experience any force

81
Q

How can you find the size of a force

A

Force = magnetic flux density x current x length (of conductor)

82
Q

Describe how a motor works

A
  • forces (which act on current in magnetic field) act on two arms of a current carrying coil
  • they act in opposite directions so coil rotates
  • the split ring commutator swaps the contacts every half turn to keep motor rotating in same direction
83
Q

how can the direction of a motor be reversed

A

by swapping the polarity of the D.C supply or swapping the magnetic poles over

84
Q

What is a solenoid

describe the field lines:

A

a long coil of current carrying wire

- the field lines around each separate coil of wire line up in same direction so the field is strong and uniform

85
Q

what is electromagnetic induction in terms of Potential difference

A

induction of potential difference in a wire which is experiencing a change in magnetic field

86
Q

what two situations can you get electromagnetic induction

A

when electrical conductor (coil of wire) and magnetic field are relative to each other
-this can be done by rotating/ moving/ changing polarity of magnet

when magnetic field through conductor changes (like in a transformer)
-this can be done by increasing STRENGTH of magnetic field, increasing SPEED, increasing TURNS ON COIL

87
Q

How does a transformer work

A

-use electromagnetic induction to change size of Potential difference of an alternating current by: increasing number of coils on secondary coil than primary coil in step down

88
Q

How do dynamos work

A
  • generate a direct current by applying a force to rotate coil in magentic field (like in a motor)
  • current is induced in coil which changes direction every half turn due to split ring communicator to keep current flowing in same direction
89
Q

How do Alternators work

A
  • similar way to dynamos, force applied to rotate coil in magnetic field with an induced current in coil
  • but instead of split ring has slip rings and brushes so the contacts dont swap every half turn which produces and alternating current
90
Q

How do microphones work

A
  • using electromagnetic induction

- sound waves hit diaphragm which is attached to coil of wire which makes both move creating a current in the coil

91
Q

How do loudspeaker work

A

-coil wrapped around pole of permanent magnet
so a.c signal causes a force on the coil
-when current reversed the force acts i different direction
-this moves the paper cone as it vibrates it as pressure causes sound waves

92
Q

Describe how a power station generates electricity for the national grid

A
  • burning fuel heats water which creates steam
  • steam powers turbine
  • turbine connected to powerful magnet inside generator
  • the magnet spins, inducing a large voltage and a.c current and single output generated
  • generator joined to national grid
93
Q

How are transformers used

A

The high current heats up wires so energy can be wasted so to reduce this transformers are used and high voltage cables.

  • Step up make Voltage really high at 400,000 V and keep current low (usually in less comercial areas like across country
  • step down decrease voltage to safe usable levels for consumers like in towns and homes
94
Q

What are the arrangements of particles in solids liquids and gases

A
  • Particles in a: gas are well separated with no regular arrangement.
  • liquid are close together with no regular arrangement. weaker forces of attraction compared to solids
  • solid are tightly packed, usually in a regular pattern. strong forces of attraction little kinetic energy so vibrate in their fixed positions
95
Q

Density does vary with …. or……

A

size or shape

96
Q

How can you find the density of an irregular solid

A

measure mass on balance

using a displacement can measure volume of water displaced

97
Q

Why do solids liquids and gases have different densities

A
  • when a substance changes state although its mass doesnt change, its volume does, so since the volume changes the value for density changes too
  • Solids are more dense
98
Q

What does heating a substance do to energy stores

A

increases energy in thermal energy store

99
Q

What is specific heat capacity

and equation

A

The amount of energy needed to change 1 kg of a substance to warm up by 1 degrees.

Change in thermal energy=mass x SHC x temp change

100
Q

Describe an experiment to measure SHC of water

A
  • measure mass of insulating container
  • fill with water and measure mass again, the difference in mass is mass of water in container
  • add joulemeter to electric immersion heater
  • measure the initial temp then turn on power
  • when temp increased by 10 degrees, record the energy on joule meter and increase in temp
  • rearrange equation and repeat 3 times to find average
101
Q

What is Specific latent heat

A

amount of energy needed to break bonds and change 1kg of a substances state

102
Q

Why does temperature not change during a state change

A

because bonds breaking/forming so energy is used to use of release energy rather than increase the temperature

103
Q

describe an experiment used to measure SPL

A
  • fill beaker with crushes ice (can insulate with lid)
  • place thermometer and record temp of ice
  • gradually heat with bunsen
  • every 20 seconds record temperature
  • continue until boiling
  • plot graph of temp against time
104
Q

Whats the equation for SPL

A

Thermal energy = mass x SLH

105
Q

how is pressure created

A

by colliding gas particles exerting a force

eg)in an enclosed system gas particles colliding with walls

106
Q

Name Two factors which effect gas pressure

A

increasing temperature increases pressure as particles have more energy in their kinetic stores so collide more
-increasing volume decreases pressure as particles get more spread and our less likely to collide

107
Q

Explain changing the pressure inside a container by heating or cooling
With balloon

A

If balloon is heated- particles gain energy and move quicker so more pressure inside balloon.
since the outward pressure of balloon is greater than inward, the balloon expands until balanced out

108
Q

Why does does work on a gas increase its temperature

A

Because it increases its internal energy, which increases its pressure
eg) can be done mechanically with bike pump
transferring energy to kinetic store which inc. inetrnal energy and heats

109
Q

what does it mean if an object has been elastically distorted?

A

It means it cant return to its original shape and length after the force has been removed

110
Q

what is an elastic limit

A

point where object stops distorting elastically and begins to distort inelastically

111
Q

if work is done on a spring where is energy transferred

A

elastic potential energy store

112
Q

what its Hookes law

A

force = spring constant x extension

113
Q

What is it called when an object stretches more for each unit of force

A

limit of proportionality

when graph becomes non-linear

114
Q

how do you calculate work done by a spring

A

energy transferred in stretching =

1/2 x spring constant x extension

115
Q

what does fluid pressure depend on

A

depth and density

as depth increases so does pressure as number of particles above that point increases

116
Q

how does pressure and density vary in water

A

pressure increases with depth

density is the same everywhere

117
Q

Equation for pressure in column of liquid=

A

height x density x GFS

118
Q

what is the resultant force called when when force exerted on bottom of object is greater than force on top

A

upthrust

119
Q

what is upthrust equal to in fluids

A

the weight of fluid displaced by object

120
Q

what makes an object float

A

if the volume of water displaced is equal to or more than its weight

usually if an object is less dense than the fluid its in then it floats

121
Q

how do submarines make use of upthrust

A

to sink they have large tanks filled with water to increases weight so its more than the upthrust
to rise the tanks are compresses with air to reduce weight so its less than upthrust

122
Q

what does atmospheric pressure decrease with

A

height / altitude

as altitude increases fewer air molecules are able to collide with surface as the atmosphere gets less dense
and weight above air decreases too

123
Q

How is atmospheric pressure created

A

by air molecules colliding with surface

A - Physics GCSE (9 decks)

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