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physics > P8 GLOBAL CHALLENGES > Flashcards

P8 GLOBAL CHALLENGES Flashcards

1
Q

what are the typical speeds for wind, sound, walking, running and cycling?

A

wind is 12m/s, walking is 1.4m/s, running is 3m/s, cycling is 5.5m/s

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2
Q

how would you estimate the magnitude of everyday accelerations?

A

first estimate the time that a change in speed, then use acceleration=change in speed/time

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3
Q

what’s a typical reaction time?

A

0.2 secs (to 0.8 s )

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4
Q

explain methods of measuring human reaction times

A

ruler drop: one person holds a ruler and the other person gets ready to catch it. the distance on the ruler indicates the reaction time.

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5
Q

which factors affect thinking distance?

A

drugs/tiredness, distracted by others in car, eating/drinking, using a radio/satnav

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6
Q

which factors affect braking distance?

A

speed, mass of car, condition of tyres

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7
Q

explain the dangers caused by large decelerations

A

can cause the brakes to overheat, seatbelt exerts a large force—>compression injuries

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8
Q

what are the main energy sources available for use on earth?

A

fossil fuels, nuclear fuel, biofuel, wind, hydroelectricity, tides, sun

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9
Q

what are the 3 main areas that energy sources are used in?

A

heating, transportation, generating electricity

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10
Q

what’s the difference between non renewable and renewable sources?

A

renewable resources can naturally replenish themselves but non renewable sources can’t

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11
Q

why has our use of energy sources changed?

A

increase in population size, more use of devices that use fuels, electricity generation

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12
Q

how has our use of energy resources changed?

A

oil, gas and hydropower were used throughout the 1900s, compared to ancient uses of wood as fuel. then nuclear energy added in 1960

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13
Q

how is electrical power used in the national grid?

A

electrical power is transferred at high voltages from power stations and then transferred at lower voltages for domestic use in each locality

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14
Q

what are step up and step down transformers used for?

A

to change pd as power is transferred from power stations

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15
Q

what makes the national grid an efficient way to transfer energy?

A

power is transported around the grid at a high voltage and low current (bc more energy is dissipated to surroundings by heating when currents are higher)

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16
Q

how is number of turns of a transformer linked to power transfer?

A

more turns means greater induced voltage therefore more current + energy transferred

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17
Q

what are the advantages of power transmission at high voltages?

A

increased efficiency

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18
Q

what is the domestic supply in uk at?

A

50Hz and 230V

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18
Q

what’s the difference between direct and alternating voltage?

A

direct voltages produce a constant current that flows in 1 direction but alternating voltages’ current changes direction regularly

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19
Q

what are the different functions of live, neutral and earth mains wires?

A

the live wire carries the current at a high voltage. the neutral wire completes the circuit and provides the return path of the current. the earth wire is a safety wire and carries current away if something goes wrong

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20
Q

what are the pds between live, neutral and earth wires?

A

pd between the live and neutral wire is 230 V (the supply voltage). pd between the live and earth wire is also 230V, but there’s 0V been the neutral and earth wire

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21
Q

why is a live wire dangerous even when a switch in a mains circuit is open?

A

if the circuit was to become complete, a large pd would start and could electrocute someone. (even if no current flows)

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22
Q

what are the dangers of providing any connection between live wire and earth?

A

it would make a circuit complete from mains to earth. a shock/fire could happen

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23
Q

give examples of protection offered by insulation of devices in wires

A

if live wire becomes loose it can touch metal casing, but earth wire connects the case to a pole in the ground so the current flows through the earth wire and not you. or, the case can be made of a plastic insulator so no current can flow through it to you (double insulated)

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24
what is red shift?
when wavelength of light is stretched, so the light shifts towards the red part of the spectrum
25
how do we know that the universe is expanding?
more distant galaxies have greater red shifts (larger increase in wavelength). shows that the more distant a galaxy is from us, the faster it recedes into space
26
what happens to wavelength as a light source moves away from you?
wavelength increases and frequency decreases
27
how is red shift linked to the big bang model?
scientists can detect low frequency microwave radiation coming from all directions and parts of the universe (CMBR). this may be leftover energy from the big bang. red shift is linked because stars and galaxies appear to be moving away from a central point
28
what does CMBR stand for?
cosmic microwave background radiation
29
how was the sun formed?
from dust and hydrogen gas drawn together by gravity
30
how did the formation of the sun cause fusion reactions?
the central core got very hot and eventually particles were moving fast enough for nuclear fusion to startha
31
what did the energy released during fusion cause?
equilibrium between gravitational collapse and expansion: a balance between gravitational attraction and expansion of hot gases outwards
32
what are the life cycles of large stars?
nebula, protostar, main sequence star, red supergiant, supernova, neutron star, black hole
33
what are the life cycles of a small star?
nebula, protostar, main sequence star, red giant, planetary nebula, white dwarf
34
what is a nebula?
a cloud of dust and gas
35
when does a protostar form?
when gravity forces the hydrogen gas and dust together. temp rises and eventually hydrogen nuclei form helium nuclei through nuclear fusion and massive amounts of energy is given out
36
when does a main sequence star form?
star enters a period of equilibrium: energy released by nuclear fusion causes outward pressure that tries to expand the star but this is balanced by the force of gravity pulling everything inwards (gravitational collapse). sun is in this period
37
when does a red giant form?
hydrogen in the core starts to run out and fusion of heavier elements happens. star swells and turns red
38
when does a red supergiant form?
bigger stars form red supergiants. as they undergo more fusion they glow brighter and expand and contract several times, forcing even heavier elements in various nuclear reactions
39
when does a supernova form?
when red supergiants run out of fuel to fuse, they collapse in on themselves in a massive explosion
40
when does a neutron star form?
exploding supernovae throw the outer layer of dust and gas into space, leaving a dense core called a neutron star
41
when does a planetary nebula form?
when a red giant runs out of fuel, it becomes unstable and ejects its outer layer of dust and gas as a planetary nebula
42
when does a white dwarf form?
a planetary nebula leaves behind a hot, dense solid core which cools down and eventually fades away
43
when does a black hole form?
after a neutron star forms, if it's big enough it becomes a black hole: a super dense point in space that even light can't escape from
44
which bodies emit radiation?
ALL!
45
what does the intensity and wavelength distribution of radiation emitted by bodies depend on?
temperature of the body
46
what can hot objects emit?
a range of EM radiation at dif energy values (and therefore dif frequencies and wavelengths)
47
what are the 8 planets?
mercury, venus, earth, mars, jupiter, saturn, uranus, neptune (my very easy method just speeds up naming)
48
what's a minor planet?
anything that isn't a planet/comet in orbit around the sun, including asteroids and dwarf planets eg pluto
49
what is geostationary orbit?
satellites which have a high orbit over earth's equator and orbit once every 24 hrs. they stay above the same point on earth's surface. used for communications
50
what is polar orbit?
satellites sweep low over both poles while earth rotates beneath them. orbit in less than 2 hours. used for weather, maps, surveillance
51
give an example of a natural satellite
moon
52
for circular orbits, how can the force of gravity lead to changing velocity but unchanged speed?
velocity is a vector quantity that depends on speed and direction: direction is constantly changing during circular orbits
53
in a stable orbit, how must the radius change if the speed changes?
if speed of satellite increases, radius of orbit decreases. at a higher speed, the satellite needs a greater force of gravity to prevent it flying off into space: so by moving closer to earth, the gravitational force on the satellite is greater and the satellite remains in a stable orbit
54
how is the temperature of a body related to the balance between incoming radiation absorbed and radiation emitted?
temp increases when body absorbs radiation faster than it emits
55
which factor determine the temperature of the earth?
concentration of greenhouse gases
56
what causes a swimming pool to remain at a constant temperature?
if it absorbs and emits the same amount of radiation
57
how does earth's atmosphere affect EM radiation from the sun that passes through it?
sun emits em radiation. some reflects off earth's atmosphere, some is absorbed by atmosphere and some reaches earth itself. some radiation absorbed by earth is re-emitted from earth
58
what are the 2 main types of seismic waves?
p and s
59
explain p waves
longitudinal waves that travel through solids and liquids. refract slowly as density of mantle changes and refract sharply at the boundary between the mantle and core
60
explain s waves
transverse waves that can only travel in solids. travel more slowly than p waves. can't pass through liquid outer core
61
how does sonar work?
a transmitter and receiver on a boat send out and detect pulses of sound waves. when the sound waves reach a boundary eg between sea and seabed, they are reflected back towards the boat. by timing how long it takes the reflected waves to return, distance to the seabed/an object can be calculated
62
how can scientists use seismic waves to work out properties of earth?
some seismic waves are reflected at boundaries and some are refracted. when the wave speed changes abruptly, there's usually a change in property. so you can see how the properties of earth change

physics (8 decks)

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