Physics HL Paper 2
A room is at a constant temperature of 300 K. A hotplate in the room is at a temperature of 400K and loses energy by radiation at a rate of P. What is the rate of loss of energy from the hotplate when its temperature is 500 K?
(5^3-3^3)/(4^3-3^3)P
Explain how this graph is consistent with the Big Bang model of the universe.
(Big Bang theory predicts that CMB will) correspond to the black-body at 3K ; the graph is of a black-body curve; stefan boltzmann law
nuclide
(a species of atom that is characterized by) the constitution of its nucleus
State what is meant by a travelling (progressive) wave.
(a wave) that transfers energy between points (in a medium)
define escape speed
(minimum) speed of object to escape gravitational field of a planet/travel to infinity; at surface of planet; without (further) energy input;
The average power absorbed per unit area at the Earth's surface is 240Wm−2 . State two reasons why the value calculated in (b)(ii) differs from this value (1400Wm-2)
- (albedo of Earth means) some radiation is reflected - Earth's surface is not always normal to incident radiation - some energy lost as radiation travels to Earth
Explain why a constant force is required to move the rod at constant speed.
- (at constant speed) forces are balanced - force is (electro) magnetic due to current in rod - which arises from induced emf from motion
Outline why the particles must be accelerated to high energies in scattering experiments.
- E = hf /energy is proportional to frequency - frequency is inversely proportional to wavelength - high energy gives small wavelength to match the small nuclear size - overcome repulsive force from the nucleus - greater precision in measurement of the size of the nucleus
An asteroid strikes the Earth and causes the orbital speed of the Earth to suddenly decrease. Suggest the ways in which the orbit of the Earth will change
- KE will initially decrease so total energy becomes more negative - Earth moves closer to Sun - new orbit with greater speed but lower energy - changes ellipticity of orbit
Outline, with reference to energy changes, the operation of a pumped storage hydroelectric system.
- PE of water is converted to KE of moving turbine to electrical energy in generator - pump water back during night / when energy is not in demand
Outline how the Schrödinger model of the hydrogen atom leads to the idea of discrete electron energy states.
- Schrödinger suggests that electron has wave properties - this (probability) wave has to conform to boundary conditions - only certain wavelengths that lead to a standing wave are allowed (by these boundary conditions) - energy is determined by wavelength of electron / standing wave determines electron energy
Outline processes and energy changes that occur through which thermal energy is produced. (nuclear power station)
- U-235 fissions / neutrons are produced - nuclei have high energy/are fast moving - nuclei transfer (kinetic) energy to (reactor) core / neutrons transfer (kinetic) energy to moderator - core/moderator energy transferred to coolant
A nuclear power station uses uranium-235 (U-235) as fuel. Outline the processes and energy changes that occur through which thermal energy is produced
- U-235 fissions / neutrons are produced - nuclei/neutrons have high energy and transfer (kinetic) energy to (reactor) core - neutrons transfer (kinetic) energy to moderator - core/moderator energy transferred to coolant
Outline why uranium ore needs to be enriched before it can be used successfully in a nuclear reactor.
- U-238 is much more common than U-235 in ore - U-235 is more likely to undergo fission - U-238 absorbs neutrons - U-238 reduces reaction rate in reactor;
The graph shows the variation with frequency of the percentage transmittance of electromagnetic waves through water vapour in the atmosphere. Suggest, with reference to resonance, the possible reasons for the sharp reduction in percentage transmittance at a wavelength of 5μm.
- X is a natural frequency (of oscillation) of water molecule - so resonance effects mean that molecules are excited at this frequency and energy is removed - less energy transmitted from electromagnetic waves at this (particular) frequency
State what is meant by a wavefunction.
- a function whose (absolute squared) value may be used to calculate the probability of finding a particle (electron) near a given position
The electrons emitted from the photo-cathode have an associated de Broglie wavelength. Describe what is meant by the de Broglie wavelength.
- all particles/electrons exhibit wave properties/have an associated wavelength (called the de Broglie wavelength) - the wavelength is equal to the Planck constant divided by the momentum of the particle λ = h/p
You are given a graph of a modulated interference pattern with maxima and secondary maxima. How do you find the distance between slits from the graph?
- angle of first maximum - lambda = d sin(theta)
The fixed mass of gas is heated from temperature T1 to T2 at constant volume. Explain why, if this fixed mass of gas is heated from T1 to T2 at constant pressure, the amount of energy required is different.
- at constant volume internal energy increases (but no work is done) - at constant pressure internal energy increases and work is done to expand (against the atmosphere)/by the gas - therefore energy required is greater at constant pressure
Outline why a beta particle has a longer range in air than an alpha particle of the same energy.
- beta have smaller mass / greater speed than alpha - beta have smaller charge than alpha - therefore less likely to interact with air molecules
The two cables in part (c) are suspended a constant distance apart. Explain how the magnetic forces acting between the cables vary during the course of one cycle of the alternating current (ac).
- cable attract whenever current is in same direction - current direction in both wires is always the same but reverses every half cycle - force varies from 0 to maximum - force is a maximum twice in each cycle
The cable between the satellites cuts the magnetic field lines of the Earth at right angles.Explain why satellite X becomes positively charged.
- cable is a conductor and contains electrons - electrons experience a force when moving in a magnetic field - use of a right hand rule to show that satellite Y becomes negative, so X becomes positive
State one way in which a real gas differs from an ideal gas.
- can be liquefied - forces exist between molecules not in contact - molecules have finite size - does not obey PV nRT for all values of P, V and T
State and explain whether the turns of wire will attract or repel one another.
- current in one turn produces magnetic field in region of adjacent turn - this gives rise to force in adjacent turn which also has electric current - they attract
Carbon-14 (C-14) is a radioactive isotope which undergoes beta minus (β-) decay to the stable isotope nitrogen-14 (N-14). Energy is released during this decay. Explain why the mass of a C-14 nucleus and the mass of a N-14 nucleus are slightly different even though they have the same nucleon number.
- decay products include an electron that has mass - products have energy that has a mass equivalent - mass defect/binding energy converted to energy of decay products «so» mass C-14 > mass N-14
Why were quarks theorized?
- deep inelastic scattering - explains the decay of neutron into proton - incorporates conservation rules
explain how such spectra give evidence for the existence of discrete atomic energy levels
- each wavelength corresponds to the energy of the photon emitted - when an electron makes a transition from a higher to lower energy level - since only discrete wavelengths/finite number of wavelengths are present, then only discrete energy levels are present
Why are real transformers not ideal?
- eddy current heating in core (changing magnetic fields induces eddy currents in the core flowing in the opposite direction (Lenz's law). This reduces the overall magnetic field and therefore current in secondary coil) - joule heating (resistance in wires produces heat) - magnetic hysteresis - flux loss
State assumptions made in determining the magnitude of the electric field between the base of the thundercloud and the ground.
- edge of thundercloud parallel to ground - thundercloud and ground effectively of infinite length - permittivity of air same as vacuum
A rod made of conducting material is in a region of uniform magnetic field. It is moved horizontally along two parallel conducting rails X and Y. The other ends of the rails are connected by a thin conducting wire. Describe, with reference to the forces acting on the conduction electrons in the rod,how an emf is induced in the rod.
- electrons are moving at right angles to the magnetic field - electrons experience a force directed along the rod / charge is separated in the rod - the work done by this force to achieve this separation leads to an induced emf
A plastic rod XY is held at end X. The end Y is rubbed with a piece of cloth and, as a result, the end Y becomes electrically charged. Explain these observations in terms of the properties of conductors and insulators.
- electrons transferred from/to the cloth from/to the rod because the body is a conductor - will flow to/from Earth leaving the rod neutral
Satellite X must release ions into the space between the satellites. Explain why the current in the cable will become zero unless there is a method for transferring charge from X to Y.
- electrons would build up at satellite Y / positive charge at X - preventing further charge flow by electrostatic repulsion - unless a complete circuit exists
Explain why, when the shower unit is switched on, the initial current in the heating element is greater
- element is cold when first switched on - therefore, smaller resistance than when hot (and so current is larger)
Not all stored energy can be retrieved because of energy losses in the system
- fluid resistance in pipe/turbine - sound energy losses from turbine - thermal energy loss - water requires KE to leave the system so not all can be transferred
A book is released from rest and falls towards the surface of Earth. Discuss how the conservation of momentum applies to the Earth-book system. [3]
- forces on Earth and book are equal and opposite / no external force acts on the system - changes in momentum of Earth and book are equal and opposite / net force on Earth-book system is zero - hence momentum of Earth-book system stays the same/is always zero and so is conserved
State and explain the differences between the pattern on the screen due to the grating and the pattern due to the double slit.
- fringes are further apart because the separation of slits is much less - intensity does not change across the pattern / diffraction envelope is broader because slits are «much» narrower - the fringes are narrower/sharper because there are more slits - intensity of peaks has increased because more light can pass through
Distinguish between hadrons and leptons.
- hadrons experiences strong force - leptons do not experience the strong force - hadrons made of quarks / not fundamental - hadrons decay into protons
Role of the heat exchanger of the reactor and the turbine in the generator of electrical energy
- heat exchanger allows transfer of (thermal) energy between reactor and coolant - coolant transfers (thermal) energy to steam/other named fluid - steam/fluid allows turbine to drive generator/dynamo
Particles can be used in scattering experiments to estimate nuclear sizes. (i) Outline how these experiments are carried out.
- high energy particles incident on thin sample - detect angle / position of deflected particles - maximum and minimum number of particles
Explain why electricity transported with high voltage
- higher V means lower I «for same power» - thermal energy loss depends on I or is ∝ I^2 so thermal energy loss will be less
state the effect of inserting a dielectric into a capacitor on the voltage across the capacitor
- higher permittivity = higher capacitance - C=q/V - q increases but voltage stays the same
Explain how readings on the high resistance ac voltmeter can be used to compare the rms values of alternating currents in different cables.
- if the coil position/orientation relative to the cables is the same in all measurements - if the coil distance from the cables is the same in all measurements - the voltage measured across the coil is proportional to current in the cable
Outline the difference between the molecular structure of a solid and a liquid.
- in solid state, nearest neighbour molecules cannot exchange places - in liquid, bonds between molecules can be broken and re-form
Outline how the expansion of the universe ultimately made it possible for stable nucleiand atoms to exist.
- in the early universe the (average) kinetic energy was very high breaking apart any nuclei/atoms/too high for atoms to form / as universe expands it cools down allowing nuclei in atoms to form;
describe formation of standing wave
- interference of traveling & reflected wave - oppositely moving traveling waves - maximum corresponds to antinode/maximum displacement «of air molecules» OR complete cancellation at node position
Outline how energy losses are reduced in the core of a practical transformer.
- laminated core reduces eddy currents - less thermal energy is transferred to the surroundings
Explain, with reference to Einstein's model, which graph corresponds to the light with greater frequency
- light consists of photons whose energy depends on the frequency - hence the energy available to the (photo)electrons will depend on f - the potentials VA and VB correspond to a measure of the maximum kinetic of the emitted electrons - the work function (of metal)/energy to emit electron is same for both light sources - as electrons in A have more kinetic energy available, this frequency must be higher
concept of temperature
- measure of average kinetic energy of particles - indicates direction of (natural) flow of thermal energy - internal energy measured in J and temperature measured
find velocity of projectile launched energetically. velocity = u with an angle of 35 degrees
- need to start at t=0 to include KE from horizontal component. Not at maximum height. (i.e. not v = (2gh)^0.5) 0.5mu^2 + mgh = 0.5mv^2 v = (u^2 + 2gh)^0.5
Why can the wave model of light not account for the photoelectric effect?
- no electrons are emitted below a threshold frequency - KE of electrons depends on frequency - wave model predicts that photoelectrons are emitted at all frequencies as wave energy depends on intensity
Suggest two disadvantages of using solar power to provide energy for heating water.
- no/little power at night - power fluctuates according to weather conditions/cloud - seasonal changes - very large surface area required
State the importance of plutonium-239.
- plutonium is also fissionable - can be used as fuel for (fast breeder) reactor
State two assumptions of the kinetic model of an ideal gas.
- point molecules / negligible volume - no forces between molecules except during contact - random motion - elastic collisions - collision in zero time
The electron is replaced by a proton which is also released from rest at X. Compare, without calculation, the motion of the electron with the motion of the proton after release. You may assume that no frictional forces act on the electron or the proton.
- proton moves to the right/they move in opposite directions - proton accelerates less than electron initially because mass is greater - field is stronger on right than left as lines get closer - proton acceleration increases as it is moving into stronger field
The daughter nuclei of U-235 undergo radioactive decay until eventually a stable isotope of lead is reached. Explain why the nuclei of U-235 are unstable whereas the nuclei of the lead are stable.
- protons repel;binding energy/strong force holds nucleus together - neutron excess / n:p ratio is greater in lead therefore overall balance of forces is more attractive in lead than uranium
The train travels away from a loudspeaker that is emitting sound waves of constant amplitude and frequency towards a reflecting barrier.The graph shows the variation with time of the output voltage from the sounds sensor.Explain how this effect arises.
- reflection at barrier leads to two waves travelling in opposite directions - formation of standing wave maximum corresponds to antinode - complete cancellation at node position
Radiation with a greater photon energy than that in (b) is now incident on the photocell. The intensity of this radiation is the same as that in (b).Describe the change in the number of photons per second incident on the surface of the photocell.
- same intensity of radiation so same total energy delivered per square metre per second - light has higher photon energy so fewer photons incident per second
Explain which interaction is responsible for this decay.
- strange quark changes favour to an up quark - changes in quarks happen only by the weak interaction
Discuss how the frequency of the radiation emitted by a black body can be used to estimate the temperature of the body.
- the (peak) wavelength of emitted em waves depends on temperature of emitter/reference to Wein's Law - so frequency/color depends on temperature
One of the coils of a particular transformer is connected in series with a switch and a battery. The coil has low resistance. On closing the switch it is observed that the current takes a certain amount of time to reach its final constant value. Explain this observation with reference to Faraday's law and Lenz's law.
- the current gives rise to a magnetic field/flux in the coil - from Faraday's law a time changing field/flux induces an emf - Lenz's law says that the direction of the induced emf is such as to oppose the growth of the current
The alpha particles produced in alpha decay have discrete energies. Suggest how this observation provides evidence for the existence of nuclear energy levels.
- the different alpha particle energies represent decay of a nucleus to different energy states of a daughter nucleus - since the energies of the alpha are discreet it means that the energy levels of the daughter nucleus must be discrete
Describe the mechanism by which thermal energy is produced in filament
- the electric field inside wires causes electrons to accelerate - electrons collide with atoms in wires - this increases the KE of atoms in wires - this increases temperature
Positrons and gamma photons are emitted in the decay of the radioactive isotope potassium-40 (K-40) to the stable isotope argon (Ar). (i) Outline the origin of gamma photons in this decay.
- the gamma photon originates from the argon nucleus - the (argon) nucleus relaxes from an excited state / to its ground state /making it stable
Explain why the electron moves at a constant speed
- the magnetic force does not do work on the electron hence does not change the electron's kinetic energy - the magnetic force/acceleration is at right angles to velocity
Suggest, with reference to uncertainty in energy difference, why the photons emitted in transitions from the first excited state of hydrogen to the ground state will, in fact, have a small range of wavelengths.
- the wavelength of the photons is determined by the difference in energy between the two levels - and that energy difference is not well defined (because of the uncertainty principle)
Suggest why the photons emitted in transitions from the first excited state of hydrogen to the ground state will, in fact, have a small range of wavelengths.
- the wavelength of the photons is determined by the difference in energy between the two levels - and that energy difference is not well defined because of the uncertainty principle
Define emf
- the work done per unit charge - from one terminal of a cell to the other / all the way round the circuit (Award only 1/2 marks for "energy per unit charge provided by the cell"/"power per unit current")
Explain, in terms of electrons, what happens to the resistance of the cable as the temperature of the cable increases.
- there is greater vibration of the metal atoms - increased collision of electrons - drift velocity decreases, so current decreases - as V is constant, R increases
Suggest why there must be an electric field inside a current-carrying conductor.
- to have a current electrons must be accelerated/move along the wire - and so a (electric) force must act on them - this is provided by the electric field
Satellite Y orbits closer to the centre of Earth than satellite X. Outline why satellite Y requires a propulsion system.
- to stop Y from getting ahead - to remain stationary with respect to X - otherwise will add tension to the cable / damage satellite
Explain, using Faraday's law of induction, how the transformer steps down the voltage.
- varying voltage/current in primary coil produces a varying magnetic field - this produces a change in flux linkage / change in magnetic field in the secondary coil - a «varying» emf is induced in the secondary coil - voltage is stepped down as there are more turns on the primary than the secondary
Suggest how the difference between λS and λE helps to account for the greenhouse effect.
- wavelength of radiation from the Sun is shorter than that emitted from Earth - infrared radiation emitted from Earth is absorbed by greenhouse gases in the atmosphere - this radiation is re-emitted in all directions including back to Earth - this WARMS the earth
The copper wires and insulator are both exposed to an electric field. Discuss, with reference to charge carriers, why there is a significant electric current only in the copper wires.
- when an electric field is applied to any material, it acts to accelerate any free electrons - electrons are the charge carriers in copper - metals/copper have many free electrons whereas insulators have no free electrons
Describe how emission spectrum is formed
- when electron falls from higher to lower energy level - ENERGY LEVELS ARE DISCRETE - E = hf
Explain what is meant by resonance
- where driving frequency equals/close to natural frequency - the frequency at the maximum amplitude of the graph
Two wires, X and Y, are made from the same metal. The wires are connected in series. The radius of X is twice that of Y. The carrier drift speed in X is vX and in Y it is vY . What is the value of the ratio vX /vY?
0.25
A spring loaded with mass m oscillates with simple harmonic motion. The amplitude of the motion is A and the spring has total energy E. What is the total energy of the spring when the mass is increased to 3m and the amplitude is increased to 2A?
0.5k(2x)^2 = 4E Energy is independent of mass
Explain how each observation provides support for the particle theory but not the wave theory of light. 1. For light below the threshold frequency no electrons are emitted from the metal surface. 2. For light above the threshold frequency, the emission of electrons is almost instantaneous.
1. particle - photon energy is below the work function / wave of an em wave is independent of frequency 2. a single electron absorbs the energy of a single photon in an almost instantaneous interaction / wave would take longer time for the energy to build up to eject the electron
Define atomic mass unit
1/12th mass of NEUTRAL ATOM of carbon-12
A photoelectric cell is connected in series with a battery of emf 2V. Photons of energy 6eV are incident on the cathode of the photoelectric cell. The work function of the surface of the cathode is 3eV. What is the maximum kinetic energy of the photoelectrons that reach the anode?
1eV
A moon of mass M orbits a planet of mass 100M. The radius of the planet is R and the distance between the centres of the planet and moon is 22R.What is the distance from the centre of the planet at which the total gravitational potential has a maximum value?
20R = furthest from the Earth
The force on a mass of 1.0 kg falling freely near the surface of Jupiter is 25 N. State the value of the magnitude of the gravitational field strength at the surface of Jupiter.
25Nkg-1
The plane of a coil is positioned at right angles to a magnetic field of flux density B. The coil has N turns, each of area A. The coil is rotated through 180 ̊ in time t. What is the magnitude of the induced emf ?
2BAN/t
An elevator (lift) and its load have a total mass of 750 kg and accelerate vertically downwards at 2.0ms-2. What is the tension in the elevator cable?
6 kN
A parachutist of total mass 70 kg is falling vertically through the air at a constant speed of 8 m s-1. What is the total upward force acting on the parachutist?
700N
Explain the variation from Rutherford scattering
A sharp decrease in the number of scattered particles at high energies. ✓ As the energy increases the alpha particles approach closer to the nucleus and so the nuclear force acts on them, the nucleus ABSORBS some thus reducing the number that is being scattered. ✓
Describe the electric field and potential inside a charged hollow sphere
According to Gauss' law, there is no electric field There is a constant, non-zero potential
Outline what is meant by an electron wave
An electron wave is a wave whose amplitude squares corresponds to the probability of finding a particle at that point
A parallel plate capacitor is connected to an ideal voltmeter reading V = 9.0V. Explain why the capacitance does not change
An ideal voltmeter has in nite resistance. ✓ And so no charge can move through it, hence no current. ✓
State one assumption that Rutherford scattering formula is based on
Assumes that there is only electric force acting on alpha particles.
What is equivalent to specific energy of a fuel/energy density of a fuel A. density of the fuel B. 1/density of the fuel C. energy stored in the fuel/density of the fuel D. density of the fuel/energy in the fuel
B
Which of the following is evidence for the wave nature of the electron? A. Continuous energy spectrum in B- decay B. Electron diffraction from crystals C. Existence of atomic energy levels D. Existence of nuclear energy levels
B. Electron diffraction from crystals
An electron enters the region between two charged parallel plates initially moving parallel to the plates. The electromagnetic force acting on the electron A. causes the electron to decrease its horizontal speed. B. causes the electron to increase its horizontal speed. C. is parallel to the field lines and in the opposite direction to them. D. is perpendicular to the field direction.
C
Explain the change in charge and pd when a dielectric is inserted
Capacitance increases. Effect on charge and pd depends on what it is connected to. - connected to battery: V will stay same hence q increases - connected to ideal voltmeter: infinite resistance so not charge can flow. Q stays same V decreases since dielectric separates, forming small electric field in opposite direction and hence weakening the pd across total electric field
Two capacitors of different capacitance are connected in series to a source of emf of negligible internal resistance.What is correct about the potential difference across each capacitor and the charge on each capacitor?
Charge: same Potential difference: difference
Samples of different radioactive nuclides have equal numbers of nuclei. Which graph shows the relationship between the half-life t1 and the activity A for the samples?
D
Which statement about atomic spectra is not true? A. They provide evidence for discrete energy levels in atoms. B. Emission and absorption lines of equal frequency correspond to transitions between the same two energy levels. C. Absorption lines arise when electrons gain energy. D. Emission lines always correspond to the visible part of the electromagnetic spectrum.
D
An object is dropped from rest. Air resistance is not negligible. What is the acceleration of the object at the start of the motion?
Decelerating
Alpha particles with energy E are directed at nuclei with atomic number Z. Small deviations from the predictions of the Rutherford scattering model are observed. Which change in E and which change in Z is most likely to result in greater deviations from the Rutherford scattering model?
E: increase Z: decrease
Define heat
Energy that is transferred from one body to another due to a change in temperature
An ion of charge +Q moves vertically upwards through a small distance s in a uniform vertical electric field. The electric field has a strength E and its direction is shown in the diagram. What is the electric potential difference between the initial and final position of the ion?
Es
Find internal energy of the gas
Find KE and then MULTIPLY BY NUMBER OF MOLECULES
Find photoelectric current
I = q * no. electrons emitted per second
The three statements give possible reasons why an average value should be used for the solar constant. I. The Sun's output varies during its 11 year cycle. II. The Earth is in elliptical orbit around the Sun. III. The plane of the Earth's spin on its axis is tilted to the plane of its orbit about the Sun. Which are the correct reasons for using an average value for the solar constant?
I and II
A black body emits radiation with its greatest intensity at a wavelength of l max. The surface temperature of the black body doubles without any other change occurring. What is the wavelength at which the greatest intensity of radiation is emitted?
Imax/2
The radius of a wire increases. State what happens to the current and drift velocity
Important: Current stays the same because of conservation of charge Drift velocity decreases
Outline an experiment in which the de Broglie hypothesis is tested
In a Davisson-Germer type of experiment electrons that have been accelerated are directed at a crystal from which they diffract and interfere. ✓ From the interference pattern the wavelength may be determined. ✓ And this is consistent with the de Broglie formula. ✓
A beam of unpolarized light is incident on the first of two parallel polarizers. The transmission axes of the two polarizers are initially parallel. The first polarizer is now rotated about the direction of the incident beam by an angle smaller than 90°. Which gives the changes, if any, in the intensity and polarization of the transmitted light?
Intensity: Different Polarisation: same
The current I flowing in loop A in a clockwise direction is increasing so as to induce a current both in loops B and C. All three loops are on the same plane. What is the direction of the induced currents in loop B and loop C?
Loop B: anticlockwise Loop C: Clockwise
What part of a nuclear power station is principally responsible for increasing the chance that a neutron will cause fission?
Moderator
The electric force between two point charges is a fundamental force as is the gravitational force between two point masses. State one similarity between these two forces and one difference
Similarity: both follow an inverse square law Difference: - gravitational force is always attractive - gravitational force is much weaker than electric force
describe and explain the motion of projectile with air resistance
Smaller height. Smaller range. Steeper impact angle. The angle is steeper because the horizontal velocity component tends to become zero. Whereas the vertical tends to attain terminal speed and so a constant value.
What does the change in resistance depend on
Smaller resistance: - an area is larger - length is smaller
Alpha decay: explain why alpha particles cannot leave the nucleus according to classical mechanics. Explain why due to quantum mechanics, they can
TUNNELING The alpha particle must overcome an energy barrier of height 30 MeV and its total energy is less than this. ✓ Leaving the nucleus would violate energy conservation. ✓ Like all particles alpha particles have wavelike properties and are described by quantum mechanical wavefunctions. ✓ Which allow for the tunneling phenomenon in which the wavefunction leaks out into the classically forbidden region. ✓
function or iron core
The iron core confines the magnetic field lines within the core and hence into the secondary coil
In the Bohr model, electrons are confined to well-defined circular orbits. Discuss, by reference to the wave-like nature of electrons, why this is not possible in quantum mechanics
The probability wave associated with the electron implies that the electron is not an object that is localised at a particular point at a given time, but can be thought to be spread out through space like waves do. The Bohr orbit only gives the average position of the electron.
When particle X collides with a stationary nucleus of calcium-40 (Ca-40), a nucleus of potassium (K-40) and a proton are produced.Suggest why this reaction can only occur if the initial kinetic energy of particle X is greater than a minimum value.
The rest mass of the products is greater than that of the reactants energy must be given to supply this extra mass
Define the time constant tau
The time for voltage/current of capacitor to fall to 37% (1/e) of its original value as it discharges Also, the theoretical time to discharge if rate stayed the same as initial rate (draw tangent at t=0, x intercept is tau) ALSO, half-life divided by ln2
de Broglie's hypothesis
To every particle there exists a corresponding wave OF PROBABILITY. wave-matter duality. lambda = h / p
Describe how some reactors are used to produce plutonium-239.
U-238 is present U-238 captures neutron (to produce plutonium);
Advantage of using a potential divider instead of series resistors in controlling a simple circuit
Voltage can be varied from 0 to emf of the cell (assuming no internal resistance) In series resistors, voltage can only be varied from 0 to some maximum value less than the emf of the cell.
Two points illuminated by monochromatic light are separated by a small distance. The light from the two sources passes through a small circular aperture and is detected on a screen far away. The images of the two light sources are just resolved. What changes to the wavelength and the size of the aperture will definitely allow the two images to be well-resolved?
Wavelength: decrease Size of the aperture: Increase
define gravitational potential
Work Done per unit mass to move a point mass from infinity to that point
Does temperature affect the absorption spectrum of an element?
Yes, there are less absorption lines at high temperature. This is because more electrons are already excited at high temperature so the photon is not absorbed
define ideal gas
a gas in which there are no intermolecular forces Accept atoms/particles. OR a gas that obeys the ideal gas law/all gas laws at all pressures, volumes and temperatures OR molecules have zero PE/only KE
Describe the phenomenon of artificial (induced) transmutation.
a particle is fired at a nucleus;a different nucleus/nuclide/element forms
Conditions for SHM
acceleration proportional to displacement and in opposite direction of displacement FROM AN EQUILIBRIUM POINT
One of the particles produced in the decay of a nucleus of U-235 is a gamma photon.State the name of another particle that is also produced.
alpha particle
Explain how the maximum kinetic energy of the emitted electrons is determined experimentally.
apply stopping potential maximum kinetic energy = eV
drift velocity
average velocity attained by charged particles, such as electrons, in a material due to an electric field.
Wien's Law
black body radiation curve for different temperature peaks at a wavelength that is inversely proportional to the temperature.
all capacitors in series have the same amount of ...
charge voltage across capacitors varies in series. In a parallel circuit, capacitors have the same voltage across them.
State how the density of a nucleus varies with the number of nucleons in the nucleus.
constant
Define coherent light
constant phase difference and the same frequency
suggest why we need a surplus of wind turbine
efficiency is less than 100% as not all of KE of air can be transferred to KE of blades, thermal energy is lost due to friction in turbine
State what is meant by thermal radiation.
emission of (infrared) electromagnetic/infrared energy/waves/radiation
explain the reduction in the intensity of the emergent beam in an hydrogen energy level diagram
energy removed from beam; re-emitted in other directions/at other wavelengths as electrons returned to energy state;
Explain what is meant by degraded energy.
energy transferred to surroundings/from system (do not allow bald "energy lost") energy no longer available for use/cannot be used again
Derive emf = Blv
equating electric to magnetic force: qE=qvB substituting E=V/L L=width of wire E=electric field strength B=magnetic field v=velocity of electrons
rms value
equivalent direct current dissipating same power in a fixed resistor as the rms current
gravitational field strength
force per unit mass acting on a small point mass placed at the point in the field
define gravitational field strength
g = F/m The force per unit mass experienced by a point mass
Identify one process in the power station where energy is degraded.
heat exchanger allows transfer of (thermal) energy between reactor and coolant; coolant transfers (thermal) energy to steam/other named fluid; steam/fluid allows turbine to drive generator/dynamo;
A projectile is shot at 3/4 escape velocity. Find the maximum height it reaches in terms of R, the planet's radius.
important: - GPE is negative - you cannot assume g to stay constant, it varies in a radial field. Hence, solve energetically KE initial + GPE initial = GPE at max 9/16 (GMm/R) - GMm/R = -GMm/r (r=maximum distance from center) r = 16/7R so h (maximum height) = 16/7R - R = 9/7R
According to the Bohr model for hydrogen, visible light is emitted when electrons make transitions from excited states down to the state with n = 2. The dotted line in the following diagram represents the transition from n = 3 to n = 2 in the spectrum of hydrogen.Which of the following diagrams could represent the visible light emission spectrum of hydrogen?
increasing wavelength to the right
An electron enters the region between two charged parallel plates initially moving parallel to the plates. The electromagnetic force acting on the electron
is parallel to the field lines and in the opposite direction to them.
Suggest what becomes of the work done (induced emf) on the loop.
it is dissipated as thermal energy (due to the resistance) in the loop / radiation
In a mass spring system, A second identical spring is placed in parallel and the experiment in (b) is repeated. Suggest how this change affects the fractional uncertainty in the mass of the block.
k will increase T would be smaller fractional uncertainty in T would be greater, so fractional uncertainty of mass of block would be greater
SI unit of intensity
kgs⁻³
The use of alternating current (ac) in a transformer gives rise to energy losses. State how eddy current loss is minimized in the transformer.
laminated core
The diagram shows four spectral lines in the visible line emission spectrum of atomic hydrogen. Outline how such a spectrum may be obtained in the laboratory.
light from a hydrogen discharge tube is passed onto a prism/diffraction grating and then is observed on a screen/through a telescope
Outline why the beam has to be coherent in order for the fringes to be visible
light waves (from slits) must have constant phase difference
The density of the universe will determine its ultimate fate. Outline the problems associated with determining the density of the universe.
measurement of mass in a given volume is (very) uncertain/difficult; there exists dark matter that is difficult to observe;measurement of distances is uncertain/difficult;matter not uniformly distributed;
A ball of mass m is thrown with an initial speed of u at an angle q to the horizontal as shown. Q is the highest point of the motion. Air resistance is negligible. What is the momentum of the ball at Q?
mu cosθ
evB
mv2/r
thermal energy
net amount of energy transferred between two bodies at different temperatures
Outline why deviations from Rutherford scattering are observed when high-energy alpha particles are incident on nuclei.
nuclear forces act nuclear recoil occurs significant penetration into nucleus / probing internal structure of individual nucleons incident particles are relativistic
Suggest why the beta minus decay is followed by the emission of a gamma ray photon
nucleus emits the photon when it decays into the ground state «from the excited state»
isotope
nuclides (atoms of the same element) with the same proton number but different nucleon/neutron numbers
Outline why the gravitational potential is negative.
potential is defined to be zero at infinity so a positive amount of work needs to be supplied for a mass to reach infinity
An estimate of the age of the universe is 1/H where H is the Hubble constant. Suggest why 1/H overestimates the age of the universe
present value of expansion rate is used for estimate but in the past the expansion rate was greater
Cell X is replaced by a second cell of identical emf E but with internal resistance 2.0. Comment on the length of AC for which the current in the second cell is zero.
since the current in the cell is still zero there is no potential drop across the internal resistance and so the length would be the same
The fraction of the internal energy that is due to molecular vibration varies in the different states of matter. What gives the order from highest fraction to lowest fraction of internal energy due to molecular vibration?
solid > liquid > gas Gases have the most kinetic energy, not vibrational energy since they are free to move. Since atoms in a solid are confined to lattice, they possess the most vibrational energy
A train is approaching an observer with constant speed c/34. where c is the speed of sound in still air. The train emits sound of wavelength λ. What is the observed speed of the sound and observed wavelength as the train approaches?
speed of the sound: c wavelength: 33/34λ
Two identical circular coils are placed one below the other so that their planes are both horizontal. The top coil is connected to a cell and a switch. The switch is closed and then opened. What is the force between the coils when the switch is closing and when the switch is opening?
switch closing: repulsive switch opening: attractive
What is the frictional coefficient in trigonometric terms
tangent θ
Another way of finding tau -> from halflife
tau = half-life/ln2 (reciprocal equation as for lambda)
State the de Broglie hypothesis as it applies to an electron.
the electron has an associated wavelength λ given by E= hp/λ where p is its momentum
Bohr modified the Rutherford model by introducing the condition mvr = nh/2π . Outline the reason for this modification.
the electrons accelerate and so RADIATE they would therefore spiral into the nucleus/atoms would be unstable electrons have discrete/only certain energy levels the only orbits where electrons do not radiate are those that satisfy the Bohr condition (quantised angular momentum)
decay constant
the fraction of the number of nuclei that decay in one/the next second
Define magnetic flux
the product of (the magnitude of) the normal component of magnetic field strength and area through which it passes/with which it is associated φ = BAcosθ
define electrical resistance of a conductor.
the ratio of the voltage across to the current in the conductor
define principle of superposition
the resultant displacement is the vector sum of the individual components (DO NOT SAY AMPLITUDE!)
State Faraday's law of induction
the size of the induced emf is proportional to the rate of change of flux linkage
Describe what is meant by radioactive decay.
unstable nuclei change spontaneously and emit energy by the emission of alpha particles, electrons, gamma rays
principle of superposition
when 2 waves meet the resultant displacement is the vector sum of their individual displacements
Outline how eddy currents reduce transformer efficiency.
«as flux linkage change occurs in core, induced emfs appear so» current is induced - induced currents give rise to resistive forces - eddy currents cause thermal energy losses - power dissipated by eddy currents is drawn from the primary coil/reduces power delivered to the secondary
Explain, in terms of molecular motion, fall of pressure with an increase in volume
«volume has increased and» average velocity/KE remains unchanged (The idea of average must be included) «so» molecules collide with the walls less frequently/longer time between collisions with the walls Decrease in number of collisions is not sufficient for MP2. Time must be included. «hence» rate of change of momentum at wall has decreased «and so pressure has decreased»
