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physics igcse > hard questions > Flashcards

hard questions Flashcards

1
Q

define acceleration

A

change in velocity per unit time

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2
Q

explain one other way in which the air leaving the condenser is different
from the air entering the condenser

A

air is drier leaving because water vapour condenses

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3
Q

unit for impulse or momentum

A

Ns

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4
Q

The lid is removed from the bottle.
State and explain how the air pressure inside the bottle changes.

A

volume increases, air moves out of bottle, pressure decreases, until equal to pressure outside of bottle

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5
Q

Suggest why a Bluetooth headset only works well over short distances

A

radio waves lose energy get weaker with distance

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6
Q

Describe the mass and energy changes that take place during this process in a nuclear reactor. (nuclear fission)

A

nucleus converted into two smaller nuclei, smaller total mass, as converted into kinetic energy, energy increases

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7
Q

Describe how thermal energy from nuclear reactions is used to generate electricity in a power station.

A

(thermal energy-achieved from geothermal, nuclear reactions or heat from sun, or burning fossil fuels) used to heat / boil (cold) water OR make steam
* steam is at high pressure
* steam drives a turbine
* turbine (connected to and) drives a generatordue to its store of ke formed from spinning
* this turns coil of wire inside generator, moves a coil in a magnetic field producing electricity
* After the steam has spun the turbine, it is cooled in a condenser and re-enters the boiler system as water to be used again.

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8
Q

A protostar becomes a stable star when

A

inward force caused by gravitational attraction, is balanced equal to outward force caused by high temp of core

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9
Q

explain deacceleration

A

negative acceleration, decreasing velocity per unit time, rate of change in velocity

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10
Q

suggest one reason why a car wont start decelerating in 0 sec

A

thinking (reaction time) car will continue to travel at initial speed

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11
Q

why is deacceleration of the car greater than force over mass

A

air resistence acts in opposite direction to motion

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12
Q

why is the deacceleration of the car not constant

A

air resistence drag decreases with decreasing speed
resistive force changes
slow speed= bigger drag

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13
Q

state the form of energy stored in the water reservoir used to generate energy

A

gravitational

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14
Q

water flows to the turbine through a pipe of constant corss sectional area, explain why ke of water in the pipe remains constant as it flows through pipe

A

as cross sectional area is constant, volume is constant to ke= 1/2 mvˆ2, speed doesnt change as velocity and mass is constant, no changes made to pressure because temperature and area is constant

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15
Q

explain in terms of molecules how evaporation cools water in cloth

A

molecule with most ke escape surface of liquid/ cloth, molecules left have less avergae ke, cooling down temp in cloth, as they move slower. Ke is porportional to temp, thus temperature falls with decreasing ke

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16
Q

a sound wave has frequency of 1.5 MHz state and explain what type of sound wave it is

A

ultrasound, frequency above 20000 hz, above audible range

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17
Q

explain in terms of forces and motion of air molecules the cause of the motion of smoke particles

A

smoke particles constantly hit by small fast moving light air molecules, moving randomly, they exert a force due to change in momentum thus smoke particles appear to be moving in random directions in addition the smoke particles are larger heavier and slower.

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18
Q

state two ways in which transverse waves differ from longitudinal

A

transeverse waves are made up of crests and peaks, longitudinal made up of compressions and rarefractions
particles on a transverse wave ossillate perpindicular to wave direction/ energy propagation

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19
Q

typical speed of sound in water

A

1200 m/s- 1500 m/s

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20
Q

state one difference between emf and p.d

A

e.m.f= chemical to electrical energy
p.d= electrical to heat energy

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21
Q

state and explain which feature in a speed time graph shows acceleration

A

gradinet= rise/ run = change in speed/ change in time

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22
Q

state and explain acceleration in speed time graph where line is horizontal to x axis

A

acceleration= 0 because gradient= 0

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23
Q

suggest how does a train ahving a streamlined shape help to travel in high speed

A

decreases amount of air resistence it experiences

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24
Q

train took 80s to reduce speed from 84-42 m/s explain why with same braking force train takes more than 80s to reduce speed from 42 to zero m/s

A

slower the speed= less air resistence it experiences, meaning less force helping to slow train down= more time taken to slow it down

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25
Q

on wet day train travels a greater distance before stoping along tacks, train has same speed

A

friction between rail and train is reduced, train slides, takes more time to slow down thus bigger distance

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26
Q

explain function of piece of iron in transformer

A

links magnetic field of coils
better induction outlet
stronger magnetic field in secondary

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27
Q

how do you convert m…

A

m= milli
divide by 1000

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28
Q

state and explain an essential safety feature required for a transformer mounted in a metal case

A

metal case must be earthed in case wire falls off and insulation fails, or live wire touches case

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29
Q

equation that connects charge and number of electrons

A

number of electrons= charge/ charge on 1 electron

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30
Q

lead cylinder has a narrow central hole, radioactive source is passed through it, state and explain effect of the lead cylinder on radioactive source

A

beam of radiation is narrow and straight, radiation in other directions is absorbed

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31
Q

explain why force on ship due to ships engine is greater than calculated value

A

there is backward drag force

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32
Q

suggest and explain what happens to hydraulic press when some air enters oil

A

less force produced, due to fact that air can be compressed, some energy used to do that

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33
Q

what is a practical use for a thermistor

A

fire alarms

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34
Q

why does a swimmer crossing a river producing a constant forward force move at constant speed

A

forward force produced by swimmer, is balanced with backward force produced by drag or water resistance, of river bank

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35
Q

what happnes to velocity when motorcyle traveling around a bend at constant speed

A

change in velocity because of change in direction

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36
Q

explain why there must be a resultant force on motorcyclist as she travels around the bend

A

there is an acceleration,
change in momentum
force is perpendicular to motion

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37
Q

explain why ray of light does not change direction when it enters the block side

A

angle of incedence= 0 and angle of refraction=0 thus no refraction takes place

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38
Q

differences between digital and analogue waves

A

analogue waves are over a range owtte
digital consists of two values owtte

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39
Q

state advantages of using digital signals rather than analogue

A

data transmitted over longer distances
larger rate of data transmission
noise easily removed

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40
Q

what and how do we correct with converging lens

A

long sightedness, reduce focal length of eye, and focus/ converges light rays on to the back of the retina

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41
Q

why are infrared and visible radiation used in glass optical fibres

A

carry high rate of data
both are visible as glass is transparent to both visible and infrared radiation

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42
Q

what is the relationship between earth and juptiers density

A

jupiter has a lower density because made of gas, earth has a high density because its made of solid

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43
Q

what is the relationship between earth and jupiters gravitational field strength

A

jupiter has a larger mass than earth, because its volume is larger even though its density is smaller, therefore it has a bigger gravitational field strength

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44
Q

what is one measurment taken when determining the speed at which a galaxy is moving away from earth

A

redshift/ change in wavelength

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45
Q

how the distance of a far galaxy can be determined without using hubles constant

A

determining the brightness of a supernova in that galaxy

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46
Q

current voltage graph of a filament lamp and explain its shape

A

voltage=x axis
current= y axis
so curve downwards
as current increases lamp gets hotter increase in resistance, more voltage required for same increase in current owtte

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47
Q

state typical half life of alpha radioactive source

A

10-500 years

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48
Q

state typical half life for beta radioactive source

A

any number ofyears eg 20 years

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49
Q

why is beta used to measure thickness of aluminium strips in factory

A

absorption of beta radioactivity depends of thickness of aluminium strip

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50
Q

unit for hubbles constant

A

per second

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51
Q

containers with greater mass are loaded near bottom of ship, explain effect on stability

A

lower centre of gravity, means more stable

52
Q

define unit kWh

A

energy transferred in one hour at a rate of transfer of 1kw

53
Q

state two ways in which boiling differns from evaporation

A

boiling only in fixed temperature
boiling thorughout liquid

54
Q

what is emant by compression and rarefraction

A

particles closer together, region with higher particle density, higher pressure
particles further apart, region with lower particle density, lower pressure

55
Q

define potential difference

A

work done per charge through a component

56
Q

explain what happens to a circuit with a lamp with increase in temp of thermistor

A

resistance decreases, bigger voltage supplied, bright lamp

57
Q

state and explain what happens to a dc motor without a split ring or commutator when coil is vertical

A

turning effect is zero,
so coil stops and goes back way it came

58
Q

explain nuclear fission

A

large unstable nucleus splits into two smaller ones, releasing energy

59
Q

explain what is meant by redshift

A

increase in wavelength, of a galaxy moving away from earth

60
Q

state two conditions necessary for helicopter to remain in equilibrium

A

no resultant net force
no resultant net moment

61
Q

explain in terms of forces change in motion of a parchutist

A

intital acceleration due to weight
air resistance increases as speed increases
resultant force downward/acceleration decreases
constant speed when air resistance= weight

62
Q

explain what is meant by absolute 0

A

particles have least kinetic energy, lowest possible temperautre

63
Q

what is meant by a magnetic field

A

region i which a magnetic pole experiences a force

64
Q

define direction of a magnetic field

A

direction of force on north pole

65
Q

charge of alpha and charge of beta

A

charge on alpha= 3.2 * 10ˆ-19
beta= 1.6 * 10ˆ-19

66
Q

safety precautions when moving or storing radioactive sources

A

limit exposure time
increase distance from source
store in lead box
use tongs or gloves

67
Q

state what r and t in orbital speed equation for a planet mean

A

r= orbital radius
t= period

68
Q

State the main source of energy for tidal energy

A

moon

69
Q

State advantages and disadvantages of tidal power as an energy resource.

A

any one advantage from:
* renewable
* reliable or predictable
* running cost low
* does not produce (harmful) pollution.

any one disadvantage from:
* (high) cost of construction
* possible effects on (marine) life
* not available all day
* power produced doesn’t always match with peak demand
* limited number of sites
* maintenance difficult /increased corrosion (because underwater)

70
Q

This isotope of sodium has a half-life of 15 hours. The isotope of magnesium is stable
and does not undergo radioactive decay.
Suggest why these properties of the isotope of sodium and the isotope of magnesium
make this isotope of sodium suitable to detect leaks from water pipes.

A

half life of sodium is long enough
decays into something stable, meaning less hazardous to humans

71
Q

State and explain the main process by which thermal energy is transferred to the worker standing beside a hot metal block

A

radiation

electromagnetic / e-m / infrared / IR (radiation emitted from block)

travels to worker OR is absorbed by worker OR travels without needing a medium

72
Q

State the direction of the force that the N pole of magnet 2 exerts on the N pole of
magnet 1. justify

A

force (on N pole) is in direction of the (magnetic) field

73
Q

how does and LDR work?

A

light dependant resistor,
as light intensity increases, resistance decreases, increase in current flow, decrease in voltage flow

74
Q

what happens to the velocity of an object in short period of time as it accelerates downwards uniformly

A

velocity will increase in a constant rate

75
Q

explain why direction of wavefronts change in way shown
(hits a boundary at an angle, angle of incidence= 45 and refracted= 33 wavelength decreases)

A

speed changes
wave speed is smaller at right hand side
lower section of wave slows down first

76
Q

describe what is meant by direction of a magnetic field

A

direction of force on north plate, from north to south

77
Q

what is meant by emf

A

energy supplied in driving charge in a circuit
energy supplied per unit charge

78
Q

what is meant by background radiation

A

radiation which is always present, all around in our enviornment

79
Q

how does a nuclear power station work
-advantages
-disadvantages

A

just like a power plant using fuels accept water gains thermal energy from nuclear reactions
-ad= No carbon dioxide or other greenhouse gases are produced.
Each kilogram of fuel contains an enormous amount of energy (it has a high energy density).
-dis= non renewable, radioactive waste produced, risk of nuclear accidents, expensive to build power plants and take a long time to do so

80
Q

3 methods to produce electricity from water

A

tidal
wave
hydroelectric

81
Q

explain hydroelectric electricity
-advantages
-disadvantages

A

building a dam wall in the river, holds water behind a wall, there is a huge height difference, relies on water rushing downstream through pipes through turbine blades which store ke and are used to power coil of wire in generator producing electricity
ad= electricity produced 24 hours
no co2 or greenhouse gas produced
renewable
dis= dam built floods large areas destroys habitats,

82
Q

explain tidal electricity
-advantages
-disadvantages

A

same concept as hydroelectric but instead uses sea water
ad= renewable, no co2 or greenhouse gas produced, tides are easy to predict
dis= Only some places have big enough tidal changes to produce sufficient electricity in this way.
Tidal dams and machines can damage marine ecosystems and habitats.

83
Q

explain wave electricity
-advantages
-disadvantages

A

uses the movement of waves up and down to drive turbines, and to produce electricity.
ad=renewable, enviornmentally friendly, sustainable
dis= do not much electricity, only work well on windy days when more waves are present.

84
Q

explain two types of solar energy forms

A

solar panels- absorb infrared electromagnetic waves from the Sun to heat water for homes. little enviornmental impact, no production of co2, requires sun shine
solar cells-produce electricity directly from electromagnetic waves in sunlight. This can be transmitted through power lines to homes across the world, dependant on amount of sunlight, expensive, not efficient,

85
Q

winds pros and cons

A

pros- renewable, no co2 production, easy and cheap to make turbines,
cons- look and sound unpleasant, needs lots of turbines thus large area, unpredicatable

86
Q

geothermal explain

A

Cold water is fed through pipes underground and returns as steam due to the volcanic activity. The steam drives turbines to generate electricity.
Although it is renewable and environmentally friendly only a few counties in the world have geothermal energy.

87
Q

what energy sources do not use sun as producer and what are their stores instead

A

geothermal- hot rocks underground tapping into internal energy stored in molten rocks deep in earth
nucelar- energy trapped inside atoms
tidal- motion of sea caused by gravity between moon and earth

88
Q

where does the sun get its energy from

A

nuclear fusion

89
Q

state form of energy stored in batteries

A

chemical

90
Q

explain how earth wire protects user

A

if live wire touches metal case or insulation fails, current is directed towards earth through the earth wire

91
Q

sun warms road, describe how energy from sun reaches earth and warms it

A

radiation from sun, electromagnetic/ visible/ infrared, travels through space, and is absorbed by the road, increasing its temperature

92
Q

air above road is heated describe how this affects molecules of air

A

they gain ke move faster and move furhter apart

93
Q

rays of light travelling towards a lens, describe what happens to light after it passes through the lens

A

light rays meet/ intersect
all light travels towards a point
point of convergence is focal point

94
Q

state name given to a lens that produces a virtual image

A

magnifying lens

95
Q

explain why an extreme high temp is needed when forcing nuclei of hydrogen-2 and hydrogen-3 together

A

high ke is needed
they repel each other
both are positively charged

96
Q

explain how in a ac generator rotating coil continuosly causes galvonameter needle to show an alternating current

A

coil of wire cuts magnet field lines
induces an emf/ current
which is read/ shown in the galvonamter by its deflection
direction of current flow changes each 180 degrees rotation of coil

97
Q

describe how a radiation used in smoke detectors ionise air

A

alpha
collides/hits with air particles
removing its electrons

98
Q

why is alpha used instead of gamma for smoke detectors

A

gamma are more penetrating arent stopped by smoke particles like how alpha are because of low penetration
alpha is more ionising, ionises air more easily

99
Q

explain what happens to motion of a trolley when angle of ramp increases

A

speed increases, a resultant force is acting on trolley

100
Q

explain why high voltage is used to transmi t electrical power

A

heat loss depends on current, less energy lost to surrounding, weaker current is used due to high voltage, thinner wires can be used

101
Q

explain how a relay works

A

iron core becomes a magnet
iron core attracts iron armature
armature pivot moves and contact touch

102
Q

describe conduction

A

movement of thermal energy through a solid metal
due to its lattice/ particle vibration, transferring thermal energy/ charge to nieghbouring atom
free delocolsied electrons moving through the metal
transfer thermal energy when touching/ hitting other particles

103
Q

thermal energy passes into water through base of pan, identify main method by which thermal energy is transferred throughout water

A

convection

104
Q

what is meant by centre of gravity

A

place where all weight seems to act

105
Q

explain why something has an unstable strcuture

A

small tilt causes its centre of gravity to no longer be verticley above its base

106
Q

what is meant by electric field

A

region where an electric charge experiences a force

107
Q

in a electric field force is in what direction

A

towards negative

108
Q

explain why alpha particles are more ionising than beta

A

they have a bigger/stronger charge
and more kinetic energy

109
Q

explain what happnes in core of a stable star

A

nucelar fusion
joining hydrogen nuclei into helium nuclei
hydrogen atoms become helium

110
Q

state quantity used that astronomers use to determine speed at which galaxy is moving away

A

change in wavelength

111
Q

state and explain use of optical fibres in medicine

A

description of fibre passing to site to be examined
light passes down fibre AND (image) returns (to sensor / observer)
extra detail, e.g. laser light source, illuminated organ, image, camera / type of sensor

112
Q

state and explain why electrical sockets and plugs used outside need to be different from those used in room

A

can be wet, must be waterproof because water conducts electricity

113
Q

radioactive tracers emit gamma rays can be used in medicine, their half life of the source of these gamma rays are 6 hours, explain why a source of gamma rays used in this way should not have half life shorter or longer than about 6 hours

A

longer- substance active in body for a long time
shorter half-life – might be insufficient time for investigation

114
Q

explain why opening parachute doesnt reduce speed of skydiver to zero

A

no air resistance at 0 speed
still is a downward force caused by gravity

115
Q

trolley moves and slowly slows down and stops explain in terms of work done energy change that takes place as trolley slows down

A

work done due to ke
ke decreases
thermal energy produced

116
Q

explain in terms of molecules effect of increase in thermal energy on water

A

particles escape surface of water as water vapour
bonds are broken
molecules gain potential energy

117
Q

explain in terms of molecules why a liquid expands more than a solid when heated

A

greater seperation with same increase in energy, weaker forces of attraction

118
Q

internal energy of water decreases give a simple molecular account of this

A

molecules lose ke, internal energy depends on ke

119
Q

define work done

A

force * distance moved in direction of force

120
Q

why does an uncharged ball jump due to proximity of a negatively charged ball, resting on a metal table

A

electrons repelled to earth
ball positively charged
opposite charges attract

121
Q

why does ball touch the rod and fall back into table, after being attracted

A

it is negatively charged by rod
and thus repelled

122
Q

Energy change in a spring moving from stretched length to equilibrium

A

Elastic to gravitational

123
Q

Explain why thinking distance is proportional to speed

A

Thinking distance is constant

124
Q

Explain why braking distance is proportional to speed squared

A

Kinetic energy
Kinetic energy=1/2mvsquared
Word done=force/distance

125
Q

Explain how evaporation cools person

A

Thermal energy from person to liquid
Molecules with most ke leva surface of skin
Molecules with low ke move slowest remain, they have less energy

126
Q

If diameter of wire doubles what happens to reistancd

A

Divides by 4

127
Q

Explain how transformer operates

A

Alternating voltage in primary circuit cute coils producing alternating magnetic field travels through iron core into secondary coil where an output induced alternating voltage is made

physics igcse (8 decks)

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