A Level Particles 1 Exam Question a lesson How to use this pack These questions have been chosen to supplement the AQA A level particles module with at least one exam question for each lesson. You MUST complete the relevant questions after each lesson. Lesson 1.1 Inside the atom 1.2 Stable and unstable nuclei 1.3 Photons 1.4 Particles and antiparticles 1.5 Particle interactions 2.1 The particle zoo 2.2 Particle sorting 2.3 Leptons at work 2.4 Quarks and antiquarks 2.5 Conservation rules 3.1 The photelectric effect 3.2 More about photoelectricity 3.3 Collisions of electrons with atoms 3.4 Energy levels in atoms 3.5 Energy levels and spectra 3.6 Wave particle duality Score 1.1 Inside the atom Q1. Fluoride ions are produced by the addition of a single electron to an atom of fluorine . What is the magnitude of specific charge of the fluoride ion? A 3.2 × 10–26 C kg–1 B 8.4 × 10–21 C kg–1 C 5.0 × 106 C kg–1 D 4.5 × 107 C kg–1 (Total 1 mark) Q2. Which nucleus has a smaller value of specific charge than the nucleus ? A B C D (Total 1 mark) Q3. A calcium ion is formed by removing two electrons from an atom of specific charge of the calcium ion? A 3.2 × 10–19 C kg–1 B 2.9 × 10–18 C kg–1 C 4.8 × 106 C kg–1 D 4.8 × 107 C kg–1 . What is the (Total 1 mark) Q4. An atom of gains 3 electrons. What is the specific charge of the ion? A 1.80 × 107 C kg–1 B –1.80 × 107 C kg–1 C 4.19 × 107 C kg–1 D –4.19 × 107 C kg–1 (Total 1 mark) Q5. Which of the following nuclei has the smallest specific charge? A B C D (Total 1 mark) Q6. (a) The nucleus of a particular atom has a nucleon number of 14 and a proton number of 6. (i) State what is meant by nucleon number and proton number. nucleon number ________________________________________________ ______________________________________________________________ ______________________________________________________________ proton number __________________________________________________ ______________________________________________________________ ______________________________________________________________ (1) (ii) Calculate the number of neutrons in the nucleus of this atom. answer = ____________________ (1) (iii) Calculate the specific charge of the nucleus. answer = ____________________ Ckg–1 (3) (b) The specific charge of the nucleus of another isotope of the element is 4.8 × 107 Ckg–1. (i) State what is meant by an isotope. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (2) (ii) Calculate the number of neutrons in this isotope. answer = ____________________ (3) (Total 10 marks) 1.2 Stable and unstable nuclei 1. (a) (i) Determine the charge, in C, of a 239 92 U nucleus. ........................................................................................................................... ........................................................................................................................... –19 (ii) A positive ion with a 239 C. 92 U nucleus has a charge of 4.80 × 10 Determine how many electrons are in this ion. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (4) (b) nucleus A X Y Pu . 239 92 U nucleus may decay by emitting two – particles to form a plutonium State what X and Y represent and give the numerical value of each. X ....................….......................................................................................…………. ........................….......................................................................................…………. Y ....................….......................................................................................…………. ........................….......................................................................................…………. (4) (Total 8 marks) 1.3 Photons 1. (i) Calculate the energy, in J, of a photon of wavelength 4.50 × 10–7 m. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (ii) Calculate the speed of an electron which has the same wavelength as the photon in part (i). ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (Total 5 marks) 1.4 Particles and antiparticles 1. In a particle accelerator a proton and an antiproton, travelling at the same speed, undergo a head-on collision and produce subatomic particles. (a) The total kinetic energy of the two particles just before the collision is 3.2 10–10 J. (i) What happens to the proton and antiproton during the collision? (ii) State why the total energy after the collision is more than 3.2 × 10–10 J. (2) (b) In a second experiment the total kinetic energy of the colliding proton and antiproton is greater than 3.2 10–10 J. State two possible differences this could make to the subatomic particles produced. 1 ................................................................................................................................. 2 ................................................................................................................................. (2) (Total 4 marks) 1.5 Particle interactions 1. (a) A positron is emitted from a nucleus when a proton changes to a neutron in the nucleus. The Feynman diagram for this process is shown in the figure below. Identify the particles labelled A, B, C and D in the diagram. C D A B up quark particle A ............................................... particle B ............................................... particle C ............................................... particle D ............................................... (b) Name an exchange particle of the weak nuclear force. ..................................................................................................................................... (c) State one difference between the photon and the exchange particle of the weak nuclear force. ..................................................................................................................................... (Total 7 marks) 2.1 The Particle zoo Q1. (a) The positive kaon, K+, has a strangeness of +1. (i) What is the quark structure of the K+? .............................................................................................................. (1) (ii) What is the baryon number of the K+? .............................................................................................................. (1) (iii) What is the antiparticle of the K+? .............................................................................................................. (1) (b) The K+ may decay into a neutrino and an antimuon in the following way. K →v +µ + (i) + µ Complete the table using ticks and crosses as indicated in the first row. Classification K vµ µ lepton × ✓ ✓ + + charged particle hadron meson (3) (ii) In this decay, charge, energy and momentum are conserved. Give another quantity that is conserved in this decay and one that is not conserved. Conserved ............................................................................................ Not conserved ....................................................................................... (2) (c) Another possible decay of the K+ is shown in the following equation, K →π +X + (i) + Identify X by ticking one box from the following list. electron muon negative pion neutral pion neutrino neutron positron (1) (ii) Give one reason for your choice in part (i). .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. (1) (Total 10 marks) Q2. (a) (i) The K– meson has strangeness –1. State the quark composition of a meson. .............................................................................................................. (1) (ii) State the baryon number of the K– meson. .............................................................................................................. (1) (iii) What is the quark composition of the K– meson? .............................................................................................................. .............................................................................................................. (1) (b) The figure below shows a Feynman diagram for a possible decay of the strange quark. (i) Which interaction is responsible for this decay? .............................................................................................................. (1) (ii) Energy and momentum are conserved when the W – particle is produced. State two other quantities that are also conserved and one that is not. conserved ............................................................................................. conserved ............................................................................................. not conserved ....................................................................................... (3) (iii) Complete this equation for the decay of a K– meson. K– → ............. + ............. + ............. (2) (Total 9 marks) 2.2 Particle sorting 1. A + pion is composed of which combination of quarks? A ud B ud C ud D ud (Total 1 mark) 2. (a) State what is meant by the term baryon. ..................................................................................................................................... ..................................................................................................................................... (1) (b) In β– decay a neutron decays into a proton. Explain how the quark structure of the baryon changes in this process. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 3 marks) 3. (i) In the Sun, fusion reactions convert hydrogen nuclei into helium nuclei. One step of this process involves a + decay. Complete a full nuclear equation for this part of the reaction by adding nucleon and proton numbers to each particle. p → n + + + (2) (ii) Tick the appropriate boxes to indicate which particles fit which classification. baryon hadron meson lepton antimatter proton neutron + (4) (Total 6 marks) 4. Classify each of the following particles by ticking all the appropriate boxes in the table. Particle Lepton Baryon Hadron Meson Neutron, n Neutrino, υ Muon, μ (Total 3 marks) 5. The equation for – decay can be written as: n p + – + v (i) For each particle, either give its quark composition or state that fundamental particle. n .................................................................................................................................. p .................................................................................................................................. β .................................................................................................................................. v .......................................................................................................................... (2) (ii) Write a similar equation for β+ decay. (2) (Total 4 marks) 2.3 Leptons at work 1. (a) (i) How do hadrons differ from all other subatomic particles? .......................................................................................................................... .......................................................................................................................... (ii) Give the quark composition of the following particles. neutron ............................................................................................................. neutral pion ...................................................................................................... .......................................................................................................................... (iii) Classify the following as either leptons, baryons or mesons. kaon ................................................................................................................ muon ................................................................................................................ (5) (b) Which is the most stable baryon? ..................................................................................................................................... (1) (c) This table may be useful in answering the questions which follow. particle baryon number lepton number strangeness – 0 0 0 p 1 0 0 p –1 0 0 e– 0 1 0 e+ 0 –1 0 ve 0 –1 0 The particle X, which is a strange particle, decays in the following way: X – + p (i) State whether X is a meson, a baryon or a lepton. .......................................................................................................................... (ii) Use conservation laws to decide whether each of the following decays of the – is possible. Give a reason for your answer. – e+ + e (A) Is this decay possible? ................................................... reason .................................................................................................... π – p e– e (B) Is this decay possible? ................................................... reason .................................................................................................... (5) (Total 11 marks) 2.4 Quarks and antiquarks 1. (i) Name two hadrons. ..................................................................................................................................... ..................................................................................................................................... (ii) Name two leptons which are also antiparticles. ..................................................................................................................................... ..................................................................................................................................... (iii) State a possible quark structure of the pion 0. A table of the properties of quarks is given in the Data Sheet. ..................................................................................................................................... (iv) A K– kaon is a strange particle. State one characteristic of a strange particle. ..................................................................................................................................... ..................................................................................................................................... (Total 4 marks) 2. A carbon-14 nucleus undergoes – decay, forming a new nucleus, releasing a – particle and one other particle which is difficult to detect. (a) Write down the proton number and the nucleon number of the new nucleus. proton number ............................................................................................................ nucleon number .......................................................................................................... (b) Name the particle which is difficult to detect. ..................................................................................................................................... (c) Name the baryons and leptons involved in the decay. baryons ....................................................................................................................... leptons ........................................................................................................................ (d) Give the quark structure for the neutron and the proton. neutron ........................................................................................................................ proton ......................................................................................................................... Hence state the quark transformation that occurs during – decay. ..................................................................................................................................... (Total 7 marks) 3. (a) State whether or not each of the following properties of a baryon is conserved when it decays by the weak interaction. charge ................................................................................................................. baryon number ................................................................................................... strangeness ......................................................................................................... (2) (b) State, with a reason, whether or not each of the following particle reactions is possible. (i) p + – K– + + .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (ii) p + v n + e+ .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (4) (Total 6 marks) 4. (a) There are a number of ways in which u, d and s quarks and their associated antiparticles may be combined to form mesons. Use the table ‘properties of quarks’, in the Data Sheet, to complete parts (i) to (iii). (i) The kaon K– has a strangeness –1. Write down its quark composition. K– ..................................................................................................................... (ii) The kaons K0 and K+ both have strangeness +1. Write down their quark composition. K0 ..................................................................................................................... K+ ..................................................................................................................... (iii) Write down the quark composition of a proton. p ....................................................................................................................... (5) (b) In the strong interaction, K– + p K0 + K+ + X, deduce the quark composition of, and state the type of, hadron represented by X. ..................................................................................................................................... ..................................................................................................................................... (2) (c) A positive muon may decay to a positron and two neutrinos. Write down an equation representing the muon decay. + (2) (Total 9 marks) 2.5 Conservation rules Q1. Some subatomic particles are classified as hadrons. (a) What distinguishes a hadron from. other subatomic particles? ...................................................................................................................... ...................................................................................................................... (1) (b) Hadrons fall into two subgroups. Name each subgroup and describe the general structure of each. subgroup 1 ................................................................................................... ...................................................................................................................... subgroup 2 ...................................................………...................................... ...................................................................................................................... (3) (c) The following equation represents an event in which a positive muon collides with a neutron to produce a proton and an antineutrino. n + μ+ p + . Show that this equation obeys the conservation laws of charge, lepton number and baryon number. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (3) (Total 7 marks) 3.1 The photoelectric effect Q1. (a) When monochromatic light is shone on a clean cadmium surface, electrons with a range of kinetic energies up to a maximum of 3.51 × 10–20 J are released. The work function of cadmium is 4.07 eV. (i) State what is meant by work function. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. (2) (ii) Explain why the emitted electrons have a range of kinetic energies up to a maximum value. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. (4) (iii) Calculate the frequency of the light. Give your answer to an appropriate number of significant figures. answer = ................................ Hz (4) (b) In order to explain the photoelectric effect the wave model of electromagnetic radiation was replaced by the photon model. Explain what must happen in order for an existing scientific theory to be modified or replaced with a new theory. ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... (2) (Total 12 marks) Q2. When a clean metal surface in a vacuum is irradiated with ultraviolet radiation of a certain frequency, electrons are emitted from the metal. (a) (i) Explain why the kinetic energy of the emitted electrons has a maximum value. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (2) (ii) Explain with reference to the work function why, if the frequency of the radiation is below a certain value, electrons are not emitted. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (2) (iii) State a unit for work function. ............................................................................................................. (1) (b) Light energy is incident on each square millimetre of the surface at a rate of 3.0 × 10–10 J s–1. The frequency of the light is 1.5 × 1015 Hz. (i) Calculate the energy of an incident photon. answer = ....................................... J (2) (ii) Calculate the number of photons incident per second on each square millimetre of the metal surface. answer = ......................................... (2) (c) In the wave theory model of light, electrons on the surface of a metal absorb energy from a small area of the surface. (i) The light striking the surface delivers energy to this small area at a rate of 3.0 × 10–22 J s–1. The minimum energy required to liberate the electron is 6.8 × 10–19 J. Calculate the minimum time it would take an electron to absorb this amount of energy. answer = ....................................... s (1) (ii) In practice the time delay calculated in part c (i) does not occur. Explain how this experimental evidence was used to develop the particle model for the behaviour of light. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (2) (Total 12 marks) 3.2 More about photoelectricity 1. When a clean metal surface in a vacuum is irradiated with ultraviolet radiation, electrons are emitted from the metal. The following equation relates the frequency of the incident radiation to the kinetic energy of the emitted electrons. hf = + EK (a) Explain what each of the following terms represents in the above equation. (i) hf ...................................................................................................................... .......................................................................................................................... (ii) ...................................................................................................................... .......................................................................................................................... (iii) EK .................................................................................................................... .......................................................................................................................... (3) (b) (i) State what would happen to the number of photoelectrons ejected per second if the ultraviolet source were replaced by a source of red light of the same intensity but of frequency less than / h. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (ii) What would the wave theory of light predict about the effect of using the red light source instead of an ultraviolet source? .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (iii) Use the photon theory of light to explain the effect of using the red light source instead of an ultraviolet source. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (3) (c) Monochromatic radiation of wavelength 3.00 × 10–7 m ejects photoelectrons at kinetic energies of up to 3.26 × 10–19 J when incident on a clean metal surface. Calculate the work function of the metal, in J. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 8 marks) 3.3 Collisions of electrons with atoms Q2. (a) When free electrons collide with atoms in their ground state, the atoms can be excited or ionised. (i) State what is meant by ground state. .............................................................................................................. .............................................................................................................. .............................................................................................................. (1) (ii) Explain the difference between excitation and ionisation. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. (3) (b) An atom can also become excited by the absorption of photons. Explain why only photons of certain frequencies cause excitation in a particular atom. ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... (4) (c) The ionisation energy of hydrogen is 13.6 eV. Calculate the minimum frequency necessary for a photon to cause the ionisation of a hydrogen atom. Give your answer to an appropriate number of significant figures. answer ..........................................Hz (4) (Total 12 marks) 3.4 Energy levels in atoms Q1. The diagram below shows the lowest three energy levels of a hydrogen atom. (a) An electron is incident on a hydrogen atom. As a result an electron in the ground state of the hydrogen atom is excited to the n = 2 energy level. The atom then emits a photon of a characteristic frequency. (i) Explain why the electron in the ground state becomes excited to the n = 2 energy level. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. (2) (ii) Calculate the frequency of the photon. frequency = ......................................... Hz (3) (iii) The initial kinetic energy of the incident electron is 1.70 × 10−18 J. Calculate its kinetic energy after the collision. kinetic energy = ............................................ J (2) (iv) Show that the incident electron cannot excite the electron in the ground state to the n = 3 energy level. (2) (b) When electrons in the ground state of hydrogen atoms are excited to the n = 3 energy level, photons of more than one frequency are subsequently released. (i) Explain why different frequencies are possible. .............................................................................................................. .............................................................................................................. (1) (ii) State and explain how many possible frequencies could be produced. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. .............................................................................................................. (2) (Total 12 marks) 3.5 Energy levels and spectra Q1. (a) Line spectra were observed before they could be explained by theory. We now know that photons of characteristic frequency are emitted when the vapour of an element is bombarded by energetic electrons. The spectrum of the light emitted contains lines, each of a definite wavelength. Explain how • the bombarding electrons cause the atoms of the vapour to emit photons • the existence of a spectrum consisting of lines of a definite frequency supports the view that atoms have discrete energy levels. The quality of your written communication will be assessed in this question. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (6) (b) The ionisation energy of a hydrogen atom is 13.6eV. (i) State what is meant by the ionisation energy of hydrogen. ............................................................................................................. ............................................................................................................. (2) (ii) Express the ionisation energy of hydrogen in joules, giving your answer to an appropriate number of significant figures. answer = ....................................... J (3) (Total 11 marks) 3.6 Wave particle duality 1. Use data from the Data Sheet in this question. (a) (i) Define the electronvolt. .......................................................................................................................... .......................................................................................................................... (ii) Show that the speed of an electron accelerated through a potential difference of 6.0kV is 4.6 × 107 m s–1. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (4) (b) State what is meant by the duality of the nature of electrons. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (1) (Total 5 marks) 2. (a) Calculate the speed of electrons which have a de Broglie wavelength of 1.5 × 10–10 m. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) Would you expect the electrons in part (a) to be diffracted by crystals in which the atom spacing is 0.10 nm? Explain your answer. ..................................................................................................................................... ..................................................................................................................................... (2) (Total 4 marks)
