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BMSAT > Physics > Flashcards

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
Q

what are the sources of background radiation?

A

natural: rocks, cosmic rays
man-made: nuclear fallout from nuclear weapons testing & nuclear accidents

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26
Q

what is radiation dose?

A

the risk of harm to body tissues due to exposure to radiation

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27
Q

what harm does radiation cause outside & inside the body?

A

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

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28
Q

what damage do high & low radiation doses cause in cells?

A

high kills cells, causing radiation sickness
low causes mutations in cells

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29
Q

nuclear fission releases

A

energy

30
Q

where does fission energy come from?

A

energy not transferred to ke of smaller nuclei is carried away by gamma rays

ke of remaining free neutrons

31
Q

describe nuclear fusion

A

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
Q

what lenses are used to correct myopia & hyperopia?

A

myopia - concave
hyperopia - convex

33
Q

what is the period of a wave & formula?

A

time taken for one wave to pass a given point
t=1/f

34
Q

what is the frequency of a wave?

A

of waves that pass a given point per second

35
Q

what 3 things can happen to a wave at boundary b/w 2 different materials & what are their effects?

A

reflection
transmission - waves continues travelling through new material e.g. refraction
absorption - energy of waves transferred to material’s energy stores

36
Q

what is diffraction & how do certain factors effect it?

A

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
Q

what are the uses of em waves?

A

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
Q

what is total internal reflection & what are its uses?

A

an incident ray is reflected inside the more dense medium, following the law of reflection

optical fibres & endoscopes

39
Q

when does total internal reflection happen?

A

when the angle of incidence is greater than the critical angle

only when the ray travelling from more dense to less dense medium

40
Q

what is the principal focus?

A

point where all rays hitting the lens parallel to the axis meet

41
Q

how does the distance of the object from the lens affect the image produced?

A

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
Q

what are the primary & secondary colours of light?

A

red
blue
green

red+ green = yellow
blue + green = cyan
red + blue = magenta

43
Q

what is the relationship b/w temp. & rate of ir radiation?

A

the hotter an object, the greater the rate of ir radiation/emission

44
Q

define perfect black body

A

object that absorbs all radiation that hits it
no radiation is reflected or transmitted

45
Q

what is intensity

A

power per unit area
= how much energy is transferred to a given area by in a given time

46
Q

how does temperature affect intensity & wavelength of ir radiation?

A

intensity of every wavelength emitted increases
intensity increases faster for shorter wavelengths so peak wavelength decreases

47
Q

how do sound waves travel through solid & through air?

A

solid: particles vibrate
particles collide with neighbouring particles, transferring vibration
= series of vibrations

air: series of compressions & rarefactions

48
Q

what is range of human hearing limited by?

A

size & shape of eardrum
structure of ear

49
Q

what surfaces are sound waves reflected by?

A

hard, flat

50
Q

describe refraction of sound waves

A

sound waves are refracted as they enter different media
the denser the material, the faster the wave
bc wavelength changes & frequency stays constant

51
Q

what happens to ultrasound waves at boundaries b/w 2 different media & what is measured?

A

partial reflection - some of the wave is reflected & some transmitted
time taken for reflection to reach detector is measured & processed to form image

52
Q

what happens to seismic waves at boundaries inside earth?

A

some absorbed & some refracted

53
Q

p vs s seismic waves

A

p: longitudinal
faster
travel through solids & liquids

s: transverse
slower
travel through solids only

54
Q

how is the motion of gas particles related to its pressure?

A

increased

55
Q

how does doing work on an enclosed gas increase its temperature in a bike pump?

A

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
Q

what is the symbol for a thermistor?

A

see book

57
Q

what is the graphical relationship b/w p.d. & current across a filament lamp & why?

A

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
Q

important points in method to investigate I-V characteristics for ohmic conductor, filament lamp & diode

A

variable resistor

repeat & average p.d.

swap wires to reverse direction of current

59
Q

graphs of ldr light intensity vs resistance & thermistor temperature vs resistance

A

see book

60
Q

what is the resistance of 2 resistors/components in parallel?

A

lower than the resistance of the smallest resistor

61
Q

why does resistance decrease as resistors are added in parallel?

A

same p.d. more directions for current to flow in
increases total current that can flow
so decreases resistance

62
Q

how is energy transferred by moving charges?

A

work done

63
Q

what is the p.d. of the national grid?

A

400,000V

64
Q

explain sparking w electric fields/ionisation of air

A

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
Q

why does adding an iron core increase mag field strength?

A

iron core becomes an induced magnet when current is flowing

66
Q

define magnetic flux density

A

how many field lines in a given area
= shows magnetic field strength

67
Q

how is strength of magnetic field around current-carrying wire increased?

A

increase size of current
go closer to wire
increase # of coils of wire
add iron core

68
Q

describe protostar stage

A

star gets denser
temperature rises so more particles collide
H nuclei undergo nuclear fusion to He
nuclei –> keeps core hot

69
Q

describe red giant stage

A

star swells & surface cools
heavier elements up to iron are created by nuclear fusion

70
Q

describe supernova stage

A

red super giants expand & contract continually, forming elements heavier than iron by nuclear fusion
–> ejected into universe to form new planets & stars

71
Q

what are dark matter & dark energy?

A

dark matter - unknown substance holding galaxies together
dark energy - responsible for accelerated expansion of universe

BMSAT (4 decks)

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