last minute cram Flashcards
what is centre gravity/mass
the point where all the mass can considered to be concentrated
Describe an experiment to determine the
position of the centre of gravity of an irregularly
shaped plane lamina
make 2 holes in lamina near the edge. draw 2 straight lines from hole and intersection is centre of gravity.forces must be balanced for it to be in equilibrium
state hookes law
extension is directly proportional to load (if elastic limit is not yet exeeded
formula for resultant force (change in momentum perunit time
∆p/∆t
electromagnetic spectrum in order of frequency
radio, wicro, infrared, visible light, ultra violet, x rays, gamma rays
what is monochromatic light
visible light of a single frequency
what are radio waves used for
radio, television transmissions, astronomy, RFID
what are microwaves used for
satellite tv, mobile phones, microwave ovens
define waves
the transfer of energy without transferring matter
what is newtons first law
when all forces acting upon an object are balanced (equal), means the object will remain stationary or travel at terminal velocity. no resultant force
what is newtons second law
when all forces acting on an object are unbalanced; meaning there is a net/resultant force which causes the object to accelerate
what is newtons third law of motion
for every action, there is an opposing reaction (opposite reaction)
is velocity constant in circular motion?
no
7 types of stored energy
- chemical potential
- hydro
- geothermal
- nuclear
- heat
-light - wind
what is boyles law
relationship of pressure and volume (mass and temp stay constant). pressure is inversely proportional to volume
formula for boyles law
P1 x V1 = P2 x V2
what is charles law
the volume of a fixed amount (constant mass) of a gas is directly proportional to the temperature of the gas when the pressure is held constant
what is the formula for charles law
v= TK
volume = temp x constant
What is pressure law
pressure of a fixed amount is directly proportional to the temperature of a gas (volume is constant)
what is the formula of pressure law
P1/T1 = P2/T2
what is the ideal gas formula
PV = nRT
pressure x volume = moles x constant x temperature
factors affecting evaporation
- humidity
- wind speed
- temperature
- surface area
are melting , evaporation and boiling endothermic?
yes
what is conduction
main method of conduting heat in solids. occurs when heat source close to an object causes an increase in kinetic energy of particles, leading to faster particles collide with slower vibrating ions in the lattice of solid, transfering energy until thermal equilibrium is reached
2 features of insulators
- no free moving electrons
- ‘slower’ and larger particles
what is convection
flow of heat through a fluid from rising of less dense higher temperature fluid, then cooling and sinking, creating a convection current
what is radiation
flow of heat from one place to another without particle contact (electromagnetic waves)
what does an object need to do to be at constant temperature?
transfer energy away at the same rate it receives energy (thermal equilibrium)
good emitters
- black surfaces
- dull
good relectors
- white
- shiny
good absorber
black
poor absorber
white
what is the wavelength
distance between 2 conservative corresponding points
what is amplitude
the distance between the undisturbed (middle) of the wave to the crest/trough (lambda)
what is frequency
number of waves passing through a point in one second (hertz)
define transverse wave
vibrations of the particles are perpendicular to the direction of the wave
4 examples of transverse waves
water waves, light, electromagnetic waves,, seismic S waves
define longitudinal waves
vibrations of the particles are parallel to the direction of the wave (cant travel through a vacuum)
give 3 examples of longitudinal waves
sound waves, seismic P waves, pressure waves
what are 2 regions of longitudinal waves called
compression (tight) and rarefraction (spread out)
what do waves transfer
energy, information
what is reflection
occurs when a wave hits a boundary between two media and does not pass through, but stays in the original medium
what is the law of relection
angle of incidence = angle of reflection
define refraction
when a wave enters a different medium, the speed can change. this effect is called refraction and occurs when a wave passes a boundary between two different media, undergoing a change in speed
what happens during refraction
- change in wavelength (frequency stays the same)
- change in direction
what happens when waves slow down?
waves will turn slightly towards the normal (cause them to bunch up and wave length decreases)
what happens when waves speed up?
waves will turn slightly away from the normal (causes waves to spread out, causing wave length to increase)
what is diffraction
when waves pass through a narrow gap, they spread out
what happens to wavelength during diffration
remains constant
factors that affect diffraction
- smaller gap (greater diffraction(
- larger wavelength
when is diffraction most prominent
when width of the gap compared to wavelength are approximately equal
what is the refractive index
number related to speed of light in a material
what is refractive index formula
speed of light in a vacuum/speed of light in a material (always will be larger than 1)
what is snells law
when light enters a denser medium, it slows down and bends towards the normal
what is snells formula
n = sin(i)/sin(r)
refractive index = sin(angle of incidence)/sin(angle of refraction)
critical angle formula
1/sin(c)
1/sin (crictical angle)
which 3 elements are magnetic
- iron
- copper
- cobalt
difference between hard and soft iron
hard = maintains magnetism for a long time
soft = magnetized quickly, but gets demagnetized quickly when external magnetic field is removed
what is a magnetic field
the region around a magnet where a force acts on another magnet/magnetic material
what is an electrical field
region where charges experience force
which way are electric field lines pointing?
away from positive charges (toward negative charges)
what are field lines in an electric field described as?
the direction of the force on a positive charge at that point
what factor does electric fields rely on?
distance from the object (field is strongest closest)
what kind of force do objects in an electric field experience?
electrostatic force (force is vector, direction of this force depends on whether the charges are the same or opposite)
what is a conductor
material that allows charge (usually electrons) to flow through it easily
define current
rate of flow of charged particles
what makes conductors (metal) so good at conduction?
- sea of electrons carry charge through the material
what is an insulator
material that has no free charges, hence does not allow the flow of charge through them very easily
4 examples of insulators
- rubber
- plastic
- glass
- wood
if a non metal allows a charge to pass through, what happens?
not very good at conducting, however they allow a little in the form of static electricity
what happens when GLE falls?
material being tested is being a good conductor
what happens when GLE remains in place
material being tested is a poor conductor
what happens when GLE falls slowly
material being tested is a poor conductor
what is current
amount of charge passing a point in a circuit every second (charge per second)
what is direct current
electrons flow in one direction only, from negative to positive terminal
what is alternating current(AC)
direction of electron flow changes direction regularly
what is conventional current
positive terminal to negative
FINSIH MAGNETISM AND OTHERS
what is acceleration
rate of change of speed
what happens when water waves enter a shallow region
velocity and wave length decrease (frequency stays the same) direction will bend towards normal
what happens when water waves enter a deep region
velocity and wavelength increases (frequency remains the same) direction will bend away from normal
what is the conservation of energy
energy cannot be created or destroyed. energy can be transferred / transformed (between energy stores)
what is kWh
energy transferred in one hour at a rate of transfer of 1 kW
how many kilowatt kW in megawatt MW
1000
how many watts W in kilowatt kW
1000
what is a compression
region where particles are closer than normal
what is a rarefraction
region where particles are further apart than normal
what do longditudinal waves need to pass
need to pass through medium
can transverse waves pass through vacuum
yes
what is formula for emf
W/Q
what is e.m.f
electrical work done by a source that moves a unit charge through the whole circuit
why do mobile phones/wireless internet use microwaves
microwaves
can penetrate some walls and only require a
short aerial for transmission and reception
what do some satellite phones use
low orbit artificial satellites and geostationary
what does direct broadcast satellite television use
geostationary satellites
what is infrared waves used for
electric grills, short range
communications such as remote controllers
for televisions, intruder alarms, thermal
imaging, optical fibres
what is visible light waves do
; vision, photography, illumination
what does uv rays do
security marking, detecting fake
bank notes, sterilising water
what do x rays do
medical scanning, security scanners
what do gamma ray do
sterilising food and medical
equipment, detection of cancer and its
treatment
harmful exposure of microwaves lead to
internal heating of body cells
harmful exposure infrared
skin burns
harmful exposure uv
damage to surface cells and eyes, leading to skin cancer and eye conditions
harmful exposure to x ray and gamma ray
mutation or damage to cells in the body
what does bluetooth use
low energy radio waves or
microwaves because they can pass through
walls but the signal is weakened on doing so
what does optical fiber use
(visible light or infrared) are
used for cable television and high-speed
broadband because glass is transparent to
visible light and some infrared; visible light
and short wavelength infrared can carry high
rates of data
what is analogue signal
signals vary consistently (any value)
what is digital signal
can only take one of 2 states
can sound be transmitted as digital or analogue signal
both
what is the benefits of digital signaling
increased rate of transmission of data
and increased range due to accurate signal
regeneratio
describe production of sound
vibrating sources
what is echo
relection of sound waves
whats ultrasound
sound with frequency higher than 20kHz
uses of ultrasound
nondestructive testing of materials, medical scanning
of soft tissue and sonar including calculation of
depth or distance from time and wave speed
what is a magnetic field
a region in which a magnetic pole experiences a force
what way do field lines go on a magnet
north to south
hazards of electrical safety
- damaged insulation
- overheating cables
- damp conditions
- excess current from overloading of plugs, leads, single and multiple sockets
what does a mains circuit consist of
live wire, neutral wire, earth wire
what does a fuse do
protects the circuit and cabling for a double insulated appliance
4 things in background radiation
- radon gas
-rocks/building - food/drink
- cosmic rays
what is radioactive decay
change in an unstable nucleus tha can result in emission of alpha, beta or gamma radiation. these are spontaneuous and random
what is half life
e time taken for half the nuclei of that
isotope in any sample to decay
what pathway shape do planets take
elliptical
how long does it take for moon to orbit earth
one month
what does the solar system contain
- one star (sun)
- mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
- pluto (dwarf planets) and asteroids
- moons (orbit planet
- smaller bodies (comets and natural satellites)
is the sun at the centre of elliptical orbit?
no except when orbit is approximately circular
what feature are the 4 planets closest to sun
rocky and small
what are the 4 planets furtheret from sun features
gaseous and large
why do the features of the planet link to dependence of gravity, elements in interstellar clouds of gas and dust, rotation of material in the cloud and formation of an accretion disc
?
describe sun
star of medium size, mostly consists of hydrogen and helium, radiates most energy in infrared, visible and uv regions of electromagnetic spectrum
what are stars powered by
nuclear reactions that release energy and that in stable stars the nuclear reactions involve the fusion of hydrogen into helium
what are galaxies made of
billions of stars
what is light year
astronomical distance measured by the distance travelled in the vacuum of space by light in one year
one light year is equal to?
9.5 x 10^15 m
life cycle of star
(a) a star is formed from interstellar clouds of
gas and dust that contain hydrogen
(b) a protostar is an interstellar cloud collapsing
and increasing in temperature as a result of
its internal gravitational attraction
(c) a protostar becomes a stable star when the
inward force of gravitational attraction is
balanced by an outward force due to the high
temperature in the centre of the star
(d) all stars eventually run out of hydrogen as
fuel for the nuclear reaction
(e) most stars expand to form red giants and
more massive stars expand to form red
supergiants when most of the hydrogen in
the centre of the star has been converted to
helium
(f) a red giant from a less massive star forms a
planetary nebula with a white dwarf star at
its centre
(g) a red supergiant explodes as a supernova,
forming a nebula containing hydrogen and
new heavier elements, leaving behind a
neutron star or a black hole at its centre
(h) the nebula from a supernova may form new
stars with orbiting planets
what is approximate diameter of milky way
100 000 light years
what is redshift
an increase in observed wavelength of electromagnetic readiation emitted from receding stars and galaxies
is light emitted from distant galaxies redshifted in comparison with earth?
yes
redshift is evidence of what
universe is expanding, supports big bang theory
what is microwave radiation
f a specific
frequency is observed at all points in space
around us and is known as cosmic microwave
background radiation (CMBR
when was CMBR produced
shortly
after the Universe was formed and that this
radiation has been expanded into the microwave
region of the electromagnetic spectrum as the
Universe expanded
how can the distance of a far galaxy be determined by
brightness of supernova in the galaxy
what is H0
hubble constant
what is hubble constant
ration of the speed at which the galaxy is moving away from earth and its distance from earth v/d
current estimate ofH0
2.2 x 10^-18 per second
what equation represents the estimate of age of universe
d/v = 1/H0
disadvantages of nuclear power
- expensive
- risk of nuclear meltdown
- nuclear fuel is finite
- produces radioactive waste which is harmful and lasts a long time
how to correct long sightedness
convex lense
how to correct near sighedness
concave lense
what is wrong with people with far sightnedess
less curved or short eyeballs
what happens in the eye with long sightedness
long-sighted has a narrower lens with a smaller focussing power so the light rays meet and form an image behind the retina and not on it
what is wrong with an eye that has near sightedness
has a wider lens with a larger focussing power so the light rays meet and form an image in front of the retina and not on it
what does converging lense
converging lens causes rays to converge before they reach the eye so image is formed on retina not behind it
how can concave lense be used to fix near sightedness
causes the rays to diverge before they reach the eye, so the image is formed on the retina and not in front of it
process of nuclear fission
- neutron collides with unstable nucleas
- nucleus splits into 2 daughter nuclei and two or three neutrons (products)
- gamma rays also emitted
what is nuclear fission
The splitting of a large, unstable nucleus into two smaller nuclei
what is nuclear fusion
whe two light nuclei join to form a heavier nucleas
where does energy come from nuclear fusion
The energy produced during nuclear fusion comes from a very small amount of a particle’s mass converted into energy
Therefore, the mass of the product (fused nucleus) is less than the mass of the two original nuclei (reactants)
what are the initial stages of a star
nebula, protostar, stable star
what is nebula
giant interstellar cloud of dust and gas
what is a protostar
gravitational attraction within a nebula pulls the particles closer together until a hot ball of gas forms, known as a protostar
As the particles are pulled closer together the density of the protostar increases
This results in more frequent collisions between the particles which causes the temperature to increase
what is a stable star
Once the protostar becomes hot enough, nuclear fusion reactions occur within its core
The hydrogen in the core of the star is converted into helium
Every fusion reaction releases heat and light which keeps the core hot
Once a star initiates fusion, it is known as a stable star
During this stage, the star is in equilibrium as the forces acting on it are balanced
Gravitational forces act inwards
This is an attractive force which pulls the outer layers inwards
Thermal pressure acts outwards
This is exerted by the expanding hot gases inside the star as energy is released during fusion
life cycle of low mass stars
red giant, planetary nebula, white dwarf
what is white dwarf
collapsed core of red giant
what is planetary nebula
when helium in the core runs out, fusion cannot occur, star becomes unstable and core collapses under its own gravity. outer layers are ejected as planetary nebula
life cycle of high mass stars
red super giant, supernova, neutron star (blackhole)
when does star become red super giant
when helium dusion occurs
red super giant:
after helium fusion, core starts to fuse helium to carbon and then successively heavier elements are formed. core collapses and expands repetedly as reactions start and stop
what is supernova
fusion reactions inside the red supergiant cannot continue once iron is formed
The core of the star will collapse rapidly and initiate a gigantic explosion called a supernova
At the centre of this explosion, a dense body called a neutron star will form
The outer layers of the star are ejected into space forming new clouds of dust and gas (nebula)
The nebula from a supernova may form new stars with orbiting planets
The heaviest elements (elements heavier than iron) are formed during a supernova and are ejected into space
These nebulae may form new planetary systems
what is neutron star (black hole)
In the case of the most massive stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole
A black hole is an extremely dense point in space that not even light can escape from
