Physics Flashcards
formulae
see back page of spec.
what happens when a force moves an object through a distance?
energy is transferred & work is done
what is the typical speed of a:
person walking
person running
person cycling
car
train
plane
in m/s:
1.5
3
6
25
55
250
fluid
liquid or gas
newton’s first law
is resultant force is 0, stationary objects remain stationary & objects moving as constant velocity continue at constant velocity
what is inertial mass?
measure of how difficult it is to change the velocity of an object
ratio of force/acceleration
m = F/a
how many forces are needed to stretch, bend or compress an object?
more than one
why does a submerged object experience the resultant force, upthrust?
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
what is upthrust = to?
weight of fluid displaced by the object
why does atmospheric pressure decrease with height?
atmosphere decreases in density so fewer air molecules collide w object
fewer air molecules above object so weight of air above object decreases
1Nm =
1J
typical values for human reaction time
0.2 - 0.9s
method to measure & calculate human reaction time
drop ruler
measure s
v^2 - u^2 = 2as a=9.8 u=0
a=change in v / t to find t
newton’s 3rd law
when 2 objects interact, the forces exerted on each other are = & opposite
momentum before =
momentum after
equation relating force to m, v & t
F = m.change in v / change in t
what is radius of atom & nucleus?
atomic radius is 10^-10m
nuclear radius is 10,000 times smaller than atomic radius
what is the range of alpha particles in air?
a few cm
what is a beta particle?
high-speed e-
what is the range of beta particles in air?
a few metres
what is beta radiation used for & why?
to test thickness of metal sheets bc not immediately absorbed & do not penetrate whole way through
how is a beta particle written in an equation?
0
e
-1
how is a gamma ray written in an equation?
0
γ
0
activity never reaches 0
what are the sources of background radiation?
natural: rocks, cosmic rays
man-made: nuclear fallout from nuclear weapons testing & nuclear accidents
what is radiation dose?
the risk of harm to body tissues due to exposure to radiation
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
what damage do high & low radiation doses cause in cells?
high kills cells, causing radiation sickness
low causes mutations in cells
nuclear fission releases
energy
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
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
what lenses are used to correct myopia & hyperopia?
myopia - concave
hyperopia - convex
what is the period of a wave & formula?
time taken for one wave to pass a given point
t=1/f
what is the frequency of a wave?
of waves that pass a given point per second
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
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
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
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
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
what is the principal focus?
point where all rays hitting the lens parallel to the axis meet
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
what are the primary & secondary colours of light?
red
blue
green
red+ green = yellow
blue + green = cyan
red + blue = magenta
what is the relationship b/w temp. & rate of ir radiation?
the hotter an object, the greater the rate of ir radiation/emission
define perfect black body
object that absorbs all radiation that hits it
no radiation is reflected or transmitted
what is intensity
power per unit area
= how much energy is transferred to a given area by in a given time
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
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
what is range of human hearing limited by?
size & shape of eardrum
structure of ear
what surfaces are sound waves reflected by?
hard, flat
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
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
what happens to seismic waves at boundaries inside earth?
some absorbed & some refracted
p vs s seismic waves
p: longitudinal
faster
travel through solids & liquids
s: transverse
slower
travel through solids only
how is the motion of gas particles related to its pressure?
increased
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
what is the symbol for a thermistor?
see book
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
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
graphs of ldr light intensity vs resistance & thermistor temperature vs resistance
see book
what is the resistance of 2 resistors/components in parallel?
lower than the resistance of the smallest resistor
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
how is energy transferred by moving charges?
work done
what is the p.d. of the national grid?
400,000V
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
why does adding an iron core increase mag field strength?
iron core becomes an induced magnet when current is flowing
define magnetic flux density
how many field lines in a given area
= shows magnetic field strength
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
describe protostar stage
star gets denser
temperature rises so more particles collide
H nuclei undergo nuclear fusion to He
nuclei –> keeps core hot
describe red giant stage
star swells & surface cools
heavier elements up to iron are created by nuclear fusion
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
what are dark matter & dark energy?
dark matter - unknown substance holding galaxies together
dark energy - responsible for accelerated expansion of universe
