Random Double Stuff Flashcards
WAVES
difference between longitudinal and transverse waves
transverse = wave that vibrates perpendicular to the direction of the oscillation
e.g. light (EM Spectrum)
longitudinal = wave that vibrates parallel to the direction of the oscillation
e.g. sound
features of a transverse wave
all EM waves travel at same speed in _____ ______
free space
define wavefront
2 or more waves moving together have wavefronts, imaginary planes connect points on adjacent waves, vibrate together
define amplitude
maximum displacement of particles from their equilibrium position.
define wavelength
distance between a particular point on one cycle of the wave and the same point on the next cycle.
define frequency
number of waves passing a particular point per second. Is measured in Hertz (Hz).
define time period
time it takes for one complete wave to pass a particular point
waves transfer energy and information without transferring _______
matter
wavespeed =
wavelength x frequency
v = lamda x f
m/s = Hz x m
frequency =
1/time period
Explain the doppler Effect
When a car is not moving and its horn sounds, the sound waves we receive are a series of evenly spaced wavefronts.
If a car is moving, wavefronts of the sound are no longer evenly spaced.
Ahead of the car wavefronts are compressed as the car is moving in the same direction as the wavefronts. This creates a shorter wavelength and a higher frequency.
Behind the car wavefronts are more spread out as the car is moving away from the previous wavefronts. This creates a longer wavelength and a lower frequency.
properties of EM waves
Transfer energy
Are transverse waves
Travel at the speed of light in a vacuum
Can be reflected and refracted
features of a longitudinal wave
rarefactions and compressions
particles vibrate back and forth
do sound waves travel faster in solid than liquids, and faster in liquids than gases
yes
order of em waves from lowest to highest frequency
Radio Waves
Microwaves
Infrared (IR)
Visible Light
Ultraviolet (UV)
X – Rays
Gamma Rays
which has the shortest wavelength and has the lowest frequency
radio waves
which colour has the shortest wavelength and lowest frequency in the visible light spectrum
red
Uses of EM waves:
Radio Waves
Microwaves
Infrared (IR)
Visible Light
Ultraviolet (UV)
X – Rays
Gamma Rays
- radio waves: broadcasting and communications
- microwaves: cooking and satellite transmissions
- infrared: heaters and night vision equipment
- visible light: optical fibres and photography
- ultraviolet: fluorescent lamps
- x-rays: observing the internal structure of objects and materials, including for medical applications
- gamma rays: sterilising food and medical equipment.
risks of exposure to EM waves:
microwaves
infrared
ultraviolet
gamma rays
- microwaves: internal heating of body tissue
- infrared: skin burns
- ultraviolet: damage to surface cells and blindness
- gamma rays: leads to ionisation of cells causing mutation which might produce cancerous cells
How to reduce risks of:
UV
gamma
UV = stay in shade, sunglasses, sun cream
Gamma = led clothing, leave room - reduced exposure
explain journey of light ray from air into glass at angle and vice versa
Glass is denser than air, so a light ray passing from air into glass slows down. If the ray meets the boundary at an angle to the normal, it bends towards the normal.
A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.
the denser the material, the ________ that light travels
slower (bends closer to normal)
practical: investigate the refraction of light, using rectangular blocks, semi-circular blocks and triangular prisms
- Set up your apparatus as shown in the diagram using a rectangular block.
- Shine the light ray through the glass block
- Use crosses to mark the path of the ray.
- Join up crosses with a ruler
- Draw on a normal where the ray enters the glass block
- Measure the angle of incidence and the angle of refraction and add these to your results table
- Comment on how the speed of the light has changed as the light moves between the mediums.
- Repeat this for different angles of incidence and different glass prisms.
refractive index =
n =
sin (angle of incidence) / sin (angle of refraction)
sin (i) / sin(r)
practical: investigate the refractive index of glass, using a glass block
- Set up your apparatus as shown in the diagram using a rectangular block.
- Shine the light ray through the glass block
- Use crosses to mark the path of the ray.
- Join up crosses with a ruler
- Draw on a normal where the ray enters the glass block
- Measure the angle of incidence and the angle of refraction and add these to your results table
- Calculate the refractive
index - Repeat steps 2 – 7 using
a different angle of
incidence - Find an average of your
results.
practical: investigate the refractive index of glass, using a glass block
- Set up your apparatus as shown in the diagram using a rectangular block.
- Shine the light ray through the glass block
- Use crosses to mark the path of the ray.
- Join up crosses with a ruler
- Draw on a normal where the ray enters the glass block
- Measure the angle of incidence and the angle of refraction and add these to your results table
- Calculate the refractive
index - Repeat steps 2 – 7 using
a different angle of
incidence - Find an average of your
results.
describe the role of total internal reflection in transmitting information along optical fibres and in prisms
optical fibres - use light to carry digital information over long distances
explain what is the critical angle and the 3 conditions
The angle of incidence which produces an angle of refraction of 90 (refracted ray is along the boundary of the surface).
When the angle of incidence is greater than the critical angle, total internal reflection occurs (all light is reflected at the boundary).
This effect only occurs at a boundary from a high refractive index material to a low refractive index material.
When the angle of incidence is lesser than the critical angle, light partially internally reflected
when the angle of incidence is equal to critical angle, lots of internal reflection and emerging ray along surface
DEFINE critical angle
the cirtical angle is the angle of incidence within an optically denser medium when the light is refracted at 90 degrees to normal
critical angle =
c =
sin ^-1 (1/n)
refractive index =
n =
1 / sin(c)
sound waves are longitudinal waves and light is transverse waves and both can be ______ and ______
reflected and refracted
frequency range for human hearing
20–20 000 Hz
ELECTRICITY
know the units for :
current =
charge =
resistance =
time =
potential difference =
power =
current = Ampere (A)
charge = coulomb (C)
resistance = ohm (Ω)
time = second (s)
potential difference = volt (V)
power = watt (W)
Explain how fuses protects the device or user in domestic appliances
Stop the flow of current by melting if the current is too high. So protecting sensitive components and people because if the components function at too higher temperature it can cause a fire.
Explain how circuit breakers protects the device or user in domestic appliances
breakers again break the circuit if current is too high.
Explain how insulation and double insulation protects the device or user in domestic appliances
prevent people from touching exposed wires and getting shocks.
Explain how earthing protects the device or user in domestic appliances
provides a low resistance path to the earth so if some one does come into contact with a current instead of flowing through them to the earth giving them a shock it flows through the earthing wire.
why a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts
Resistance causes transfer of electrical energy to heat energy. Some components are designed to have a high resistance to make sure this happens, for example electrical heaters that have lots of resistors to ensure a high resistance so a lot of heat is produced.
Power =
P =
(watts)
current x voltage
I x V
(A) x (V)
voltage =
energy transferred / charge
J/C
what is a volt equivalent to
Joule/coulomb
J/C
how to pick which fuse is correct when given
current of fuse should be slightly higher than current in circuit - so if circuit heats up normally and fuse keeps breaking even though current isn’t too high - then fuse current is too low
fuse amps (3A, 5A, 13A)
Energy (J) =
potential difference (V) x current (A) x Time (s)
I x V x t
Alternating current:
describe the motion of the current
current constantly changes direction
Direct current:
describe the motion of the current
current flows in only one direction
is mains eletricity AC or DC supply?
what voltage, frequency and current?
AC
230V
50Hz
do batteries and solar cells supply AC or DC electricity?
how much would a typical battery supply
DC
1.5 V
why a series or parallel circuit is more appropriate for particular applications, including domestic lighting
Advantages of parallel circuits:
Components (e.g. bulbs) may be switched on/off independently.
If one component breaks, current can still flow through the other parts of the circuit.
Bulbs maintain a similar brightness.
Advantages of series circuits:
Fewer wires, cheaper and easier to assemble.
Uses less power
as voltage increases in a circuit, current also________
increases
the more components in a circuit, the _______ the current
lower
describe graph of wire, filament lamp, diode as graph shows how current varies with voltage
(resistance changed using variable resistor)
wire - directly proportionate
filament lamp - s curve
diode - horizontal line and sudden steep gradient
changing resistance in a circuit will _________ the current
decrease as V = IR
describe how resistance changes in an LDR
as light increases, resistance decreases
describe how resistance changes in a thermistor
as temperature increases, resistance decreases
how to check if there is current in a circuit
add lamp, if current is flowing, lamp will light up
current is the ….
rate of flow of charge
so I =
Q/t
Q =
Charge (C) =
I x t
electric current in solid metallic conductors is a flow of ….
negatively charged electrons - free to flow in metals so carry charge - negative electrons attracted to positive charges
why current is conserved at a junction in a circuit
At a junction current ‘splits’ to take both paths.
It comes back together when the paths meet again.
I1 = I2 + I3 +I4
how is voltage and current, resistance split in a series circuit?
voltage - split between components
current -same for each component
resistance - split between components
how is voltage and current split in a parallel circuit?
voltage - same for each component
current - split between branches
energy transferred (J) =
E =
charge (C) x voltage (V)
QV
conducting materials
Copper
Aluminium
Gold
Silver
Insulating Materials:
Glass
Air
Plastic
Rubber
Wood
MAGNETISM AND ELECTROMAGNETISM
properties of magnetically hard materials
e.g. steel
retain their magnetism once magnetised.
hard to magnetise
properties of magnetically soft materials
e.g. iron
lose their magnetism once they are no longer exposed to a magnetic field. They are used as temporary magnets such as electromagnets.
easily magnetised
define magnetic field line
(3 points)
Around every magnet there is a region of space where we can detect magnetism (where magnetic materials will be affected).
This is called the magnetic field and in a diagram we represent this with magnetic field lines.
The magnetic field lines should always point from north to south.
magnetism is induced in some materials when placed in a _________
magnetic field
describe how magnetism is induced in some materials when placed in a magnetic field
When magnetic materials are bought near or touch the pole of a strong or permanent magnet, they become magnets. This magnetic character is induced in the objects and it is removed when the permanent magnet is removed. This is a temporary magnet
Magnetism is induced in the paperclips so each paperclip can attract another one
practical: investigate the magnetic field pattern for a permanent bar magnet and between two bar magnets
Place your bar magnet in the centre of the next page and draw around it.
Place a compass at one pole of the bar magnet.
Draw a ‘dot’ to show there the compass is pointing,
Move the compass so the opposite end of the needle is pointing to the dot,
Repeat steps 3 and 4 until to reach the other pole of the magnet.
Do this procedure at least 5 times from different points on the pole of the magnet.
Tip, try to be as accurate as possible when drawing your dots
Join up your dots to create the field line plots
describe how to use two permanent magnets to produce a uniform magnetic field pattern
A uniform magnetic field is comprised of straight, parallel lines which are evenly spaced. Between two opposite charges on flat magnets, a uniform magnetic field is formed.
How to draw:
from north to south
at least 3 lines with arrows pointing n-> s
evenly spaced (measure with ruler)
draw with ruler
an electric current in a conductor produces a ________ __________around it
magnetic field
how can magnetic field direction be determined in a current travelling along a wire
Right Hand Grip Rule
A current travelling along a wire produces a circular magnetic field around the wire
Describe the construction of electromagnets
A soft iron core wrapped in wire. When current flows through the coil of wire it becomes magnetic.
draw magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current
when is there a force on a charged particle
there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
explain why there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
The movement of the charged particle is a current so it produces a magnetic field. This magnetic field interacts with the permanent magnetic field to create a force. The force is perpendicular to the direction of motion and the permanent magnetic field.
what does a split ring commutator do
A split ring commutator is used to ensure that the direction that the current flows in the coil
reverses every half turn.
A force is exerted on a current-carrying wire in a magnetic field, how is this effect applied in dc electric motors
Current flows in the wire/coil.
This creates a magnetic field around the wire/coil.
This magnetic field interacts with the field from the permanent magnet.
This produces a force on the wire/coil which moves the wire/coil.
The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning.
how to increase the turning effect (motor)
● increasing the current
● using a stronger magnetic field
● increasing the number of turns on the coil
A force is exerted on a current-carrying wire in a magnetic field, how is this effect applied in loudspeakers
An alternating current from the source passes though the coils in the speaker.
This current is constantly changing direction and magnitude
This current creates a magnetic field around the coil
This field interacts with the magnetic field from the permanent magnets
Creating a constantly changing force on the coil.
This causes the coil to vibrate in and out as the direction of the force changes, moving the cone
The cone causes vibrations which we hear as sound waves.
explain the generator effect
When there is relative movement between a conducting wire & a magnetic field, a voltage
will be induced. For example, if conducting wire moves across a magnetic field, a voltage
is induced in it. If it is part of a complete circuit, this causes a current to flow.
how to increase induced voltage
moving the wire more quickly,
- using a stronger magnetic field,
- or increasing the length of the wire inside the magnetic field (eg. by making it more
coiled).
use the left-hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
what does each finger mean
Fleming’s left hand rule.
Thumb: force
First finger: Magnetic Field
Second finger: Current
in FLHR, if current is revered or magnetic field is reversed, then force is _____________
reversed
in FLHR, if current is increased or magnetic field is increased, then force is _____________
increased
ASTROPHYSICS
Units for:
Mass =
distance =
velocity =
acceleration =
Force =
time =
gravitational field strength =
Mass = kilogram (kg)
distance = metre (m)
velocity = metre per second (m/s)
acceleration = metre per second squared (m/s2)
Force = newton (N)
time = second (s)
gravitational field strength = newton/kilogram (N/kg)
define universe
large collection of billions of galaxies
define galaxy
large collection of billions of stars
which galaxy is our solar system in
milky way galaxy
why gravitational field strength, g, varies and know that it is different on other planets and the Moon from that on the Earth
An object’s gravitational field strength depends on its MASS. A massive object, like a star, will have a very large g-field. The Moon has less mass than the Earth, so its gravitational field is much weaker – approx 1/6th of the Earth’s. This means that we could jump higher on the Moon, and objects would fall more slowly, as they experience a weaker gravitational force.
A planet with a large radius will have a ________ gravitational field at its surface, because the surface is _____ away from the centre of the planet.
weaker
further
explain how gravitational force causes the moon to orbit planets
explain how gravitational force causes the planets to orbit the Sun
explain how gravitational force causes artificial satellites to orbit the earth
explain how gravitational force causes comets to orbit the sun
describe orbit of comet
comets = highly elliptical orbits, with the Sun at one focus. When they come in close to the Sun they speed up, due to the larger gravitational force on them. They also develop bright tails that point away from the centre of the Sun. These are caused by tiny ice crystals that melt and break off from the comet and reflect the bright light of the Sun.
describe differences in orbits of planet and moons
moons = circular orbit
planets = slightly squashed circles , ellipses
orbital speed (m/s) =
2 x pi x orbital radius
how is a star’s colour is related to its surface temperature
goes from red to white
red is coldest surface temperature, white is hottest
red, orange, yellow, blue, white
describe the evolution of stars of similar mass to the Sun through the following stages: nebula, star (main sequence) , red giant, white dwarf
- nebula
Stars form from large clouds of dust and gas particles (nebulae) that are drawn together by gravitational forces over millions of years. As the particles get closer the temperature and pressure becomes so large that nuclear fusion of hydrogen nuclei to helium nuclei occurs. This releases enormous amounts of energy in the form of heat and light.
- star (main sequence)
Fusion produces forces that make the star expand outwards, but gravitational force is always pulling the particles within the star inwards. When these two opposing forces become balanced a star is stable and called a main sequence star. It should stay this way for millions of years, at a constant size and temperature.
- red giant
Eventually hydrogen fusion stops as the star runs out of fuel. Gravitational force is now bigger than the outward fusion force which causes the star to collapse inwards and compress. This causes it to heat up to even higher temperatures so that fusion of helium nuclei begins. The increased power output causes the star to expand greatly. The surface area is so large that it is cooler than before, so its colour changes to red and the star is called a red giant.
- white dwarf
Eventually fusion stops when the star runs out of helium nuclei and the gravitational force causes the star to collapse inwards and compress again. This heats it up so it changes colour to emit white light. The star is squashed so greatly by the gravitational force to become a small and very dense white dwarf. (They are so dense that a teaspoon full would weigh more than a cruise liner). A white dwarf eventually cools down and change colour as it does so, eventually becoming black.
describe the evolution of stars with a mass larger than the Sun
After the stable period, a giant star expands into red supergiant. (It produces all the elements up to iron during nuclear fusion). When it finally runs out of nuclei to fuse it collapses due to the gravitational force, and then explodes – an exploding star is called a supernova.
The explosion throws dust and gas back into space and so another nebula is formed. A dense core remains – called a neutron star, because it is made entirely from neutrons. If its mass is large enough it can compress further to become a black hole. (Their gravity is so strong that not even light can escape!)
RADIOACTIVITY AND PARTICLES
units for:
frequency of decay :
distance :
time :
frequency of decay : becquerel (Bq), 1 (Bq) for 1 decay / sec
distance : centimetres (cm), normally however is (m)
time : hour (h), minute (min) but normally (s)
describe structure of an atom
Atoms are made up of protons, neutrons and electrons.
Protons and neutrons are in the nucleus, electrons are in the shells
define:
atomic number
mass number
isotope
Atomic (proton) number is the number of protons in the nucleus of an atom.
Mass (nucleon) number is the total number of protons and neutrons in the nucleus of an atom.
An isotope is an atom of the same element, same number of protons, different number of neutrons
alpha (α) particles, beta (β−) particles, and gamma (γ) rays are ionising radiations emitted from ______ nuclei in a ______ process
unstable
random
can one radioactive source release different types of radiation?
yes
what is ionisation
when an atom loses or gains an electron, causing it to become an ion (an atom which is positively or negatively charged).
describe nature of alpha (α) particles
ionising
penetration
stopped by:
nature of radiation:
strong ionising
weak penetration
stopped by paper
nature of radiation: helium nucleus
4
He
2
describe nature of alpha (α) particles
ionising
penetration
stopped by:
nature of radiation:
moderate ionising
moderate penetration
stopped by: 5mm aluminium
nature of radiation: fast moving electron
0
e
-1
describe nature of gamma (γ) rays
ionising
penetration
stopped by:
nature of radiation:
weak ionising
strong penetration
stopped by: 10cm lead
nature of radiation: em wave
0
γ
0
practical: investigate the penetration powers of different types of radiation using either radioactive sources or simulations
Detect using a Geiger Müller Tube.
Try the three different materials in order, paper then aluminium then lead.
Count rate will significantly decrease if radiation is stopped.
explain the alpha decay process
- heavy (helium) nucleus emits an alpha particle
- nucleus changes to that of a different element
describe alpha decay in terms of atomic and mass numbers
2 protons and 2 neutrons are lost.
· Mass number decreases by 4
· Atomic number decreases by 2
explain the beta decay process
A neutron turns into a proton and emits a beta particle (electron)
The nucleus changes to that of a different element
describe beta decay in terms of atomic and mass numbers
· 1 neutron is converted to an electron (lost from the atom) and proton
· Mass number is unchanged
· Atomic number increases by 1
explain gamma decay process
After a previous decay, a nucleus with excess energy emits a gamma particle.
Gamma particles are a form of electromagnetic radiation.
describe gamma decay in terms of atomic and mass numbers
· Energy is lost from an atom in the form of an electromagnetic wave
· Mass number is unchanged
· Atomic number is unchanged
describe neutron radiation in terms of atomic and mass numbers
In neutron-rich nuclides, occasionally one or more neutrons are ejected. They are also emitted during nuclear fission.
The nucleus becomes a new isotope of the original element
Geiger Müller detector:
When connected to a counter, the detector will be able to measure _________ . Each time it absorbs radiation, it transmits an electrical pulse to the machine, which
produces a clicking sound. The greater the frequency of clicks, the more radiation present.
radioactivity
Photographic film:
Radiation will cause photographic film to ______ . They are worn as badges by people who work with radiation, to check how much exposure they have had
darken
sources of background (ionising) radiation from Earth and space
radon in air
Granite in rocks
Cosmic rays
Medical equipment - x rays from mri scanners
Food and drink containing radioactive isotopes
activity of a radioactive source ______ over a period of time and is measured in ___________
decreases
becquerels
define half life
time taken for the radioactivity of a specific isotope to fall to half its original value.
uses of radioactivity in industry
smoke detectors
thickness monitoring for metal sheets
o Smoke detectors
Long half-life alpha emitters are used in smoke detectors. Alpha particles cause a current in the
alarm. If smoke enters the detector, some of the alpha particles are absorbed and the current drops, triggering the alarm.
o Thickness monitoring
Long half-life beta emitters can be used for thickness monitoring of metal sheets. A source and receiver are placed on either side of the sheet during its production. If there is a drop or rise in the number of beta particles detected, then the thickness of the sheet has changed and needs to be adjusted.
uses of radioactivity in medicine
o Sterilisation of equipment
Gamma emitters are used to kill bacteria or parasites on equipment so it is safe for operations (this means they can be sterilised through their protective packaging to eliminate the risk of contamination).
o Diagnosis and treatment
- Short half-life gamma emitters such as technetium-99m are used as tracers in medicine as they concentrate in certain parts of the body. The half-life must be long enough for diagnostic procedures to be performed, but short enough to not remain radioactive for too long.
- Other gamma emitters such as cobalt-60 can be used to destroy tumours with a high dose
of radiation.
irradiation
what is it?
what does it do?
source?
prevention?
causes?
- object exposed to radiation but does not become radioactive
- Irradiating a material does not make that material radioactive. However, it can kill living cells
3.source is from radiation emitted outside of the object
4.prevent by using shielding, such as lead clothing
5.caused by the presence of radioactive sources outside the body
contamination
what is it?
what does it do?
source?
prevention?
causes?
Contamination:
Occurs when material that contains radioactive atoms is deposited on materials, skin, clothing, or any place where it is not desired.
- object exposed to radiation t become radioactive
- Irradiating a material does not make that material radioactive. However, it can kill living cells
3.source is from radiation emitted outside of the object
4.prevent by using shielding, such as lead clothing
5.caused by the presence of radioactive sources outside the body
Alpha
describe the dangers of ionising radiations, including: that radiation can cause mutations in living organisms, that radiation can damage cells and tissue, the problems arising from the disposal of radioactive waste and how the associated risks can be reduced.
Beta
describe the dangers of ionising radiations, including: that radiation can cause mutations in living organisms, that radiation can damage cells and tissue, the problems arising from the disposal of radioactive waste and how the associated risks can be reduced.
low-activity sources used in smoke alarms
Gamma
describe the dangers of ionising radiations, including: that radiation can cause mutations in living organisms, that radiation can damage cells and tissue, the problems arising from the disposal of radioactive waste and how the associated risks can be reduced.
define nuclear fission
splitting of a large and unstable nucleus into two smaller and more
stable nuclei to produce energy. This is the method currently used in nuclear power stations
define nuclear fusion
process where lighter atoms are forced to join together to make heavier atoms. This releases energy.
what is radioactive decay
random process involving unstable nuclei emitting radiation to become more stable.
nuclear fusion, nuclear fission and radioactive decay all can be sources of ________
energy
what are the products of nuclear fission and what is released
the process of splitting a nucleusa uranium-235 nucleus absorbs a thermal (slow-moving) neutron, it splits into two
daughter nuclei and 2 or 3 neutrons, releasing energy in the process.
what can the products of nuclear fission do
neutrons then can induce further fission events in a chain reaction by striking other
uranium-235 nuclei
describe uses in a nuclear reactor :
control rods
moderator
reactor
- boron - absorbs neutrons and keeps number of neutrons that only one fission neutron per event goes on to induce further fission
- water - slows down neutrons by collisions so they move slow enough to be absorbed by another u-235 nucleus
- thick steel vessel - withstands high pressure and temperatures and absorbs some radiation. has concrete walls that act as radiation shields to absorb all radiation escaping reactor core
define chain reaction
neutrons then can induce further fission events in a chain reaction by striking other uranium-235 nuclei
how to dispose of radioactive waste
geographically stable, sealed in glass blocks in lead lined boxes, buried deep underground
away from people as could leach into groundwater amd contaminate soil, rivers and drinking water
explain process of nuclear reactor
substance pumped around reactor
energy from fission transfers the energy to water by heating
water into steam
steam turns turbine
turbine turns generator
generator produces electricity
explain process of nuclear fusion
the process of fusing two nuclei to form a larger nucleus, results in a loss of mass from smaller nuclei and release of energy
how do sun and stars release energy
nuclear fusion
why does nuclear fusion not occur at low temperatures
● Nuclear fusion does not happen at low temperatures and pressures because the
electrostatic repulsion of the protons is too great.
FORCES AND MOTION
v^2 =
u^2+2as
a =
v - u / t
practical: investigate the motion of everyday objects such as a toy car or tennis ball
Apparatus: stop watch and metre rule
1.mark the start and end positions for the know distance
2.use a metre rule to measure the distance
3.line up front of car with start point, release and start timer
4.move eyes to end point
5.stop timer when front of car passes end point
6.improve by repeating and averaging
7.make sure car starts from stationary
8.calculate average speed using : average speed = distance travelled/ time taken
