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Physics Flashcards

1
Q

formulae

A

see back page of spec.

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2
Q

what happens when a force moves an object through a distance?

A

energy is transferred & work is done

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3
Q

what is the typical speed of a:
person walking
person running
person cycling
car
train
plane

A

in m/s:
1.5
3
6
25
55
250

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4
Q

fluid

A

liquid or gas

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5
Q

newton’s first law

A

is resultant force is 0, stationary objects remain stationary & objects moving as constant velocity continue at constant velocity

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6
Q

what is inertial mass?

A

measure of how difficult it is to change the velocity of an object
ratio of force/acceleration
m = F/a

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7
Q

how many forces are needed to stretch, bend or compress an object?

A

more than one

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8
Q

why does a submerged object experience the resultant force, upthrust?

A

pressure of fluid exerts force of object from every direction
pressure increases with depth so force exerted on bottom of object is greater than the force exerted in the top of the object

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9
Q

what is upthrust = to?

A

weight of fluid displaced by the object

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10
Q

why does atmospheric pressure decrease with height?

A

atmosphere decreases in density so fewer air molecules collide w object
fewer air molecules above object so weight of air above object decreases

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11
Q

1Nm =

A

1J

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12
Q

typical values for human reaction time

A

0.2 - 0.9s

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13
Q

method to measure & calculate human reaction time

A

drop ruler
measure s
v^2 - u^2 = 2as a=9.8 u=0
a=change in v / t to find t

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14
Q

newton’s 3rd law

A

when 2 objects interact, the forces exerted on each other are = & opposite

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15
Q

momentum before =

A

momentum after

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16
Q

equation relating force to m, v & t

A

F = m.change in v / change in t

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17
Q

what is radius of atom & nucleus?

A

atomic radius is 10^-10m
nuclear radius is 10,000 times smaller than atomic radius

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18
Q

what is the range of alpha particles in air?

A

a few cm

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19
Q

what is a beta particle?

A

high-speed e-

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20
Q

what is the range of beta particles in air?

A

a few metres

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21
Q

what is beta radiation used for & why?

A

to test thickness of metal sheets bc not immediately absorbed & do not penetrate whole way through

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22
Q

how is a beta particle written in an equation?

A

0
e
-1

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23
Q

how is a gamma ray written in an equation?

A

0
γ
0

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24
Q

activity never reaches 0

A
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25
what are the sources of background radiation?
natural: rocks, cosmic rays man-made: nuclear fallout from nuclear weapons testing & nuclear accidents
26
what is radiation dose?
the risk of harm to body tissues due to exposure to radiation
27
what harm does radiation cause outside & inside the body?
outside: irradiation most dangerous beta & gamma most dangerous bc penetrate the body inside: contamination most dangerous alpha most dangerous bc damage localised area due to high ionising power
28
what damage do high & low radiation doses cause in cells?
high kills cells, causing radiation sickness low causes mutations in cells
29
nuclear fission releases
energy
30
where does fission energy come from?
energy not transferred to ke of smaller nuclei is carried away by gamma rays ke of remaining free neutrons
31
describe nuclear fusion
2 lighter nuclei collide at high speed & join to form a heavier nucleus e.g. H —> He heavier nuc. mass is smaller than total mass of lighter nuc. so mass converted to energy
32
what lenses are used to correct myopia & hyperopia?
myopia - concave hyperopia - convex
33
what is the period of a wave & formula?
time taken for one wave to pass a given point t=1/f
34
what is the frequency of a wave?
of waves that pass a given point per second
35
what 3 things can happen to a wave at boundary b/w 2 different materials & what are their effects?
reflection transmission - waves continues travelling through new material e.g. refraction absorption - energy of waves transferred to material’s energy stores
36
what is diffraction & how do certain factors effect it?
the spreading out of waves when they go through a gap or past the edge of a barrier the larger the gap, the smaller the diffraction the greater the wavelength, the greater the diffraction wavelength does not change
37
what are the uses of em waves?
radio: diffract around earth’s curved surface TV, radio, Bluetooth microwaves: satellite signals e.g. TV in microwave - penetrates few cm into food then absorbed by water molecules, transferring energy to the stores ir: ir camera electric heaters, toasters visible: optical fibres - work due to reflection of light rays back and forth until they reach end of fibre uv: fluorescent lights tanning beds security pens x-rays: pass easily through tissue but not through bone or metal so gives image radiotherapy to treat cancer gamma: medical tracers sterilisation food preservation radiotherapy to treat cancer
38
what is total internal reflection & what are its uses?
an incident ray is reflected inside the more dense medium, following the law of reflection optical fibres & endoscopes
39
when does total internal reflection happen?
when the angle of incidence is greater than the critical angle only when the ray travelling from more dense to less dense medium
40
what is the principal focus?
point where all rays hitting the lens parallel to the axis meet
41
how does the distance of the object from the lens affect the image produced?
an object at 2f: real, inverted image same size as object @ 2f an object b/w 2f & f: real, inverted image bigger than object beyond 2f an object closer than f: virtual, upright image on same side of lens
42
what are the primary & secondary colours of light?
red blue green red+ green = yellow blue + green = cyan red + blue = magenta
43
what is the relationship b/w temp. & rate of ir radiation?
the hotter an object, the greater the rate of ir radiation/emission
44
define perfect black body
object that absorbs all radiation that hits it no radiation is reflected or transmitted
45
what is intensity
power per unit area = how much energy is transferred to a given area by in a given time
46
how does temperature affect intensity & wavelength of ir radiation?
intensity of every wavelength emitted increases intensity increases faster for shorter wavelengths so peak wavelength decreases
47
how do sound waves travel through solid & through air?
solid: particles vibrate particles collide with neighbouring particles, transferring vibration = series of vibrations air: series of compressions & rarefactions
48
what is range of human hearing limited by?
size & shape of eardrum structure of ear
49
what surfaces are sound waves reflected by?
hard, flat
50
describe refraction of sound waves
sound waves are refracted as they enter different media the denser the material, the faster the wave bc wavelength changes & frequency stays constant
51
what happens to ultrasound waves at boundaries b/w 2 different media & what is measured?
partial reflection - some of the wave is reflected & some transmitted time taken for reflection to reach detector is measured & processed to form image
52
what happens to seismic waves at boundaries inside earth?
some absorbed & some refracted
53
p vs s seismic waves
p: longitudinal faster travel through solids & liquids s: transverse slower travel through solids only
54
how is the motion of gas particles related to its pressure?
increased
55
how does doing work on an enclosed gas increase its temperature in a bike pump?
the gas applies pressure to the plunger of the pump, which exerts a force on it work is done mechanically against this force when pushing down on the plunger this transfers energy to the ke stores of the gas particles, which increases the temp. of the gas
56
what is the symbol for a thermistor?
see book
57
what is the graphical relationship b/w p.d. & current across a filament lamp & why?
see book electrical charge transfers some energy to thermal stores of filament lamp so temp. increases so resistance increases so less current can flow per unit p.d. so graph gets shallower
58
important points in method to investigate I-V characteristics for ohmic conductor, filament lamp & diode
variable resistor repeat & average p.d. swap wires to reverse direction of current
59
graphs of ldr light intensity vs resistance & thermistor temperature vs resistance
see book
60
what is the resistance of 2 resistors/components in parallel?
lower than the resistance of the smallest resistor
61
why does resistance decrease as resistors are added in parallel?
same p.d. more directions for current to flow in increases total current that can flow so decreases resistance
62
how is energy transferred by moving charges?
work done
63
what is the p.d. of the national grid?
400,000V
64
explain sparking w electric fields/ionisation of air
high enough p.d. b/w charged object & earthed conductor high p.d. = strong electric field b/w charged object & earthed conductor electrons in air particles are removed so air is ionised current flows through it
65
why does adding an iron core increase mag field strength?
iron core becomes an induced magnet when current is flowing
66
define magnetic flux density
how many field lines in a given area = shows magnetic field strength
67
how is strength of magnetic field around current-carrying wire increased?
increase size of current go closer to wire increase # of coils of wire add iron core
68
describe protostar stage
star gets denser temperature rises so more particles collide H nuclei undergo nuclear fusion to He nuclei --> keeps core hot
69
describe red giant stage
star swells & surface cools heavier elements up to iron are created by nuclear fusion
70
describe supernova stage
red super giants expand & contract continually, forming elements heavier than iron by nuclear fusion --> ejected into universe to form new planets & stars
71
what are dark matter & dark energy?
dark matter - unknown substance holding galaxies together dark energy - responsible for accelerated expansion of universe

BMSAT (4 decks)

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