Physics Exam Pointers/Key Points

Why is it necessary that large groups of scientists work on projects?
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Why is it necessary that large groups of scientists work on projects?
-Results must independently peer reviewed and validated before they're accepted
-Many skills across many different scientific disciplines are needed
-Helps spread out the cost for more expensive projects (eg particle accelerators)
What must be done to validate an unconfirmed scientific theory?
-The theory must be independently tested with experimentation

-The experiment and results must be repeatable
To improve precision in an experiment, you can make _______ ______ __________
full scale readings
What type of photons/electromagnetic radiation does mercury emit when it de-excites?
(High energy) Ultraviolet
Describe the motion of an object moving down a slope
-It will be accelerating due to the force of its weight
-Acceleration is greatest at the top, lowest at the bottom
-The component of weight parallel to the slope decreases until non of it's parallel
Describe the changes in momentum when rainwater falls into a moving truck
-Rain loses vertical momentum as it falls
-Gains horizontal momentum when in the truck
-Truck increases in mass
-But there are no external hotizontal forces
-So the truck's speed decreases to conserve momentum
Why can an electron only be excited by photons of specific frequency but can be excited by electrons of varying energy
-An exact amount of energy is needed for excitation of an electron
-Photons have discrete amounts of energy
-All of a photon's energy is absorbed in a 1 to 1 interaction with the electron
-A colliding electron can transfer some of its energy for excitation and continue moving with a lesser KE
For a beam in equilibrium, why must the centre of mass be directly under the point where the cables meet?
-The point is a pivot
-In order for there to be no turning effect, the beam's weight's line of action must align with the pivot
Explain what you see when two separate wavelengths (eg λ and 1.2λ) undergo double slit
-Central fringe is a mixture of both colours
-Separate fringes of each wavelength/colour are on the side
-Lower wavelength is closer to the middle
-Spacing of larger wavelength = 1.2 x the smaller wavelength spacing
-5th fringe of the 1.2λ light overlaps 6th fringe of 1λ light
When an experimental value increases, what happens to percentage uncertainty?
It decreases
When an experimental value decreases, what happens to percentage uncertaintyIt increases, as uncertainties take make up a percentage of smaller measure meants (e.g 1±0.01 has a smaller % uncertainty than 0.1±0.01)Why does a path difference lead to interference in waves?-A path difference between waves causes them to have a phase difference -This leads to constructive/destructive interference when they superposeHow do vapour discharge tubes work?-A potential difference is applied across the tube -This causes electrons to be accelerated through the tube with high speeds -Electrons with sufficient speed (and thus kinetic energy) collide with gas atoms in the tube, exciting the electrons within them by transferring a sufficient amount of energy -When these electrons de-excite they release visible light photonsHow do fluorescent lights (a type of vapour discharge tube) work?-Electronics are emitted via thermionic emission (heated filament) -They're accelerated by a potential difference -These electrons collide with atoms of mercury gas -If the electrons are of sufficient energy they cause excitation in the mercury atoms' electrons -When these electrons de excite they emit UV photons -These are absorbed by the atoms of the phosphor coating, exciting its electrons -When these electrons de excite they release visible lightWhat is the formula for energy of a spring that obeys Hooke's law/the potential energy of an object on a spring in SHM?E = (0.5)kx² Where -k is the spring constant of the spring -x is displacement from equilibrium (or Amplitude, A, when at the maximum displacement)What is the three (3) quark model for hadrons?-Hadrons consist of mesons and baryons (made from quarks, which allow them to experience Strong nuclear force) -Mesons are made of a quark-antiquark pair -Baryons are made from 3 quarks (antibaryons are made from 3 antiquarks) -An example of a baryon is a proton (most stable baryon) w/ an up up down composition -Quarks cannot exist on their ownExplain why there are only 4 combinations of quarks that result in charged mesons-State the charges of the three (u, d, s) quarks: -Up = (+2/3)e, down = (-1/3)e, strange = (-1/3)e -A combination of quark and antiquark are needed to create a meson -A meson with a charge of +𝟏 requires either: ( up antidown ) or ( up antistrange ) -A meson with a charge of -𝟏 requires either ( anti-up down ) or ( anti-up strange )What are the different ways you can ensure a light ray does not deviate from its path as travels materials?-Make it pass along the normal of the material(s) -Ensure the materials are of the same refractive index/optical density -Make sure that the materials are in contact (so the light does not have to pass through air/a gap)What does it usually indicate when a value (e.g. refractive index) only changes by a few percent?The change has little effect or won't have significant effectWhy does the reading on a voltmeter decrease when external resistance is lowered in a circuit?-Voltage supplied is constant -Therefore a decrease in resistance causes an increase in current -Additionally, the internal resistance (which is constant) now makes up a greater proportion of total resistance -Thus more voltage is lost to internal resistanceExplain the process of pair production-A high energy gamma photon interacts with a nearby nucleus -In doing so, its energy is used to create a corresponding particle antiparticle pair -The particle and antiparticle move in opposite directions to conserve momentumExplain why pair production cannot take place if the frequency of the photon is below a certain value.-The photon must have energy greater than or equal to the total rest energy of the particle and antiparticle formed -The photon's energy is dependent on its frequency (E = hf) -Thus if frequency is too low the photon will have insufficient energy for pair productionDescribe the apparatus and procedure used for determining how a wire's resistance varies from 100°C to 0°C-You need a circuit set up with an ammeter in series and voltmeter in parallel (alternatively use an ohm meter) -The wire should be placed in a water bath with water initially at 100°C -A thermometer should also be in the water bath to measure temperature -When the water is heated, stir it to ensure the temperature distribution is uniform -Add ice to decrease the temperature -Find resistance using either V/I = R or by using an ohm meter -Plot a graph of resistance against temperatureWhat are advantages of a smaller core diameter in an optical fibre?-Decreased modal/multipath dispersion -Thus less distortion/better signal quality -There is less refraction out of the core so less light is lost -Increased probability of Total Internal Reflection as angle of incidence is less likely to fall below the critical angle -Faster/improved data transferWhen trying to determine the spring constant for a spring and you know at which load the limit of proportionality is exceeded, what should you avoid doing?Avoid reaching or exceeding the load at which the limit of proportionality is exceededWhat things can you do in an experiment to reduce uncertainty, particularly in measurements of length?-Take a minimum of 8 readings -Repeat the experiment for new readings and find an average -Use a vernier scale -Use a set square/mirror in contact with the measuring instrument to eliminate parallax errorDescribe the motion of a non-node point on a stationary wave-It will oscillate -About/perpendicular to the equilibrium positionWhy is it important to correctly align the aerial of a TV to receive the strongest possible signal?-The radiowaves transmitted to the aerial are usually polarised, so only oscillate in one plane -The aerial must be aligned in the same plane of oscillation as the transmitted wave to receive the strongest signalWhat are different sources of background radiation?-Cosmic rays -Nuclear waste -Radon gas in the atmosphere -Carbon 14 -Medical equipment (???)Define binding energyThe energy required to split a nucleus into its constituent protons and neutronsWhat does a graph of Nuclear radius, R, against Nucleon number, A, look like?Half of the graph of y = x^(1/3)How is the motion of particles at two different temperatures similar?-Both are random motion -Both have a range of speedsHow is the motion of particles at two different temperatures different?-The molecules at a higher temperature have a greater kinetic energy -They have different root mean square speeds (hotter particles are faster) -Different frequency of collisions