Physics 2018 1 Question booklet 1

• Questions 1 to 12 (56 marks) • Answer all questions • Write your answers in this question booklet • You may write on page 18 if you need more space • Allow approximately 55 minutes

Examination information

Materials • Question booklet 1 • Question booklet 2 • SACE registration number label

Reading time • 10 minutes • You may begin writing during this time • You may begin using an approved calculator during this time

Writing time • 2 hours • Use black or blue pen • You may use a sharp dark pencil for diagrams and representations • Approved calculators may be used

Total marks 116

© SACE Board of South Australia 2018

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page 4 of 18 1. Monochromatic light of wavelength 589 nm from a coherent light source is incident on two slits. The distance between the slits is 2.4  10–4 m. An interference pattern is observed on a screen. The slit-to-screen distance is 0.75 m. Calculate the distance between adjacent maxima on the screen.

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page 5 of 18 PLEASE TURN OVER 2. The diagram below shows some of the energy levels of hydrogen.

eV 0 n = ’ 0.54 n = 5

0.85 n = 4

1.51 n = 3

3.40 n = 2

13.6 n = 1

[This diagram is not drawn to scale.]

A hydrogen atom that has been raised to the n  4 excited state quickly returns to its ground state. The arrow on the diagram above represents one possible transition between energy levels.

(a) Determine the frequency of the photons that would be emitted when a hydrogen atom undergoes the transition shown on the diagram.

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(b) (i) On the diagram above, show one way that the hydrogen atom can return from the n  4 excited state to its ground state by emitting two photons. (1 mark)

(ii) State the region (ultraviolet, visible, or infrared) in the electromagnetic spectrum of each of the photons emitted in the transition that you drew in part (b)(i).

First photon emitted: ______

Second photon emitted: ______(2 marks)

page 6 of 18 eV' 3. (a) Derive the formula f , for the maximum frequency of X-rays produced in a simple PD[ h X-ray tube operating at a potential difference 'V.

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(b) Using vf O and the formula in part (a), determine the minimum wavelength X-ray produced in a simple X-ray tube operating at a potential difference of 3.0  104 V.

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page 7 of 18 PLEASE TURN OVER 4. Cyclotrons are used to accelerate protons to high speeds. The diagram below represents the main components of a cyclotron.

alternating magnetic field power supply B into page

electric field E between dees

G (a) Describe how an electric field E between the dees can transfer energy to a proton passing between the dees.

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(b) A cyclotron with a magnetic field strength of magnitude 2.3 T is used to accelerate protons to a kinetic energy of 2.9  10–11 J.

(i) Calculate the period for the circular motion of the protons.

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page 8 of 18 (ii) Determine the radius at which the protons emerge from the cyclotron.

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5. An aeroplane in flight can gain a large electric charge. Static discharge wicks have sharp points and are installed on the wings and the wing tips of an aeroplane. These static discharge wicks cause charge movement away from the aeroplane via a corona discharge.

Source: Adapted from Nehrener, D 2006, ‘File: Wingletdetail.jpg’, Wikimedia Commons, the free media repository, https://commons.wikimedia.org/w/index.php?title=File:Wingletdetail.jpg&oldid=231922076

Describe how an electric field near sharp points may ionise the air.

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page 9 of 18 PLEASE TURN OVER G G 6. The diagram below shows two velocity vectors, v and v, of a particle moving with uniform circular motion.

G v1

G v2

G G Using the velocity vectors v and v , draw a labelled vector diagram showing the change G   in velocity 'v. (3 marks)

page 10 of 18 7. The generator in a particular electricity power station produces an alternating voltage of 2.50  104 V. A transformer is used to increase the voltage to 2.75  105 V, before it is fed into transmission lines. The primary coil of the transformer has 2000 turns.

(a) State whether this is a step-up transformer or a step-down transformer.

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(b) Calculate the number of turns in the secondary coil of the transformer.

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(c) State why a high voltage is used in transmission lines when electricity is transmitted over very long distances between cities.

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page 11 of 18 PLEASE TURN OVER 8. (a) An electron enters a uniform magnetic field at a right angle. It travels in a circular path with a period of 1.41  10–4 s and a radius of 0.56 m.

(i) Explain why the electron undergoes uniform circular motion.

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(ii) Calculate the speed of the electron.

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(b) A bubble chamber is used to identify charged particles. It contains a liquid that produces small bubbles that show the paths of charged particles that are travelling through it. A magnetic field is set up at right angles to the bubble chamber.

(i) Explain why a charged particle will spiral inwards within the bubble chamber.

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page 12 of 18 The diagram below shows the path of a positive alpha particle and the path of an electron within the magnetic field. Both particles were initially travelling at the same speed.

path A

path B

(ii) State which of the two particles produced path B. Give a reason for your answer.

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9. One type of charmed Xi baryon consists of one down quark, one strange quark, and one charm quark. Determine the charge of this charmed Xi baryon.

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page 13 of 18 PLEASE TURN OVER 10. If a passenger vehicle travels in a circular path at too high a speed, it can tip over. The image below shows a vehicle beginning to tip over.

A group of students investigated the speed at which a passenger vehicle will begin to tip over by using a remote-control toy car. The students hypothesised that the speed at which a remote-control toy car travelling in uniform circular motion will begin to tip over is directly proportional to the radius of its path. The graph below shows the data collected by the students:

14

12 ) 1  (m s (m

10

8

6

4 Speed at which toy car begins to tip over 2

0 01234 56 78 Radius (m)

page 14 of 18 (a) Using the graph on page 14, state whether or not the results support the students’ hypothesis. Justify your answer.

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(b) Some people think that using a remote-control toy car for this investigation is an appropriate choice. Other people think that it is an inappropriate choice. Justify one of these opinions.

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page 15 of 18 PLEASE TURN OVER 11. The diagram below shows the magnetic field produced by a current flowing in two loops of wire.

A

(a) On the diagram above, show the direction of the current in the loops of wire. (1 mark)

(b) Point A is midway between the tops of the two loops of wire. Explain why there is no magnetic field at point A.

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page 16 of 18 12. The electric field produced by a point charge in a vacuum has a magnitude of 7.5  10–2 N C–1 at a distance of 2.4  10–4 m from the point charge. Determine the magnitude of the charge.

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page 17 of 18 PLEASE TURN OVER You may write on this page if you need more space to finish your answers to any of the questions in this question booklet. Make sure to label each answer carefully (e.g. 8(a)(i) continued).

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page 18 of 18 — end of question booklet Physics 2018

Question booklet 2

• Questions 13 to 20 (60 marks) • Answer all questions • Write your answers in this question booklet • You may write on page 16 if you need more space • Allow approximately 65 minutes

2

© SACE Board of South Australia 2018

Copy the information from your SACE label here

CHECK SEQ FIGURES LETTER BIN page 2 of 16 13. The image below shows the line absorption spectra of a mixture of different atoms in a gaseous state.

Account for the presence of absorption lines in the spectra shown above.

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page 3 of 16 PLEASE TURN OVER 14. The photograph below shows a projectile launcher used by a group of students to investigate the range of a marble.

position 1

spring

The spring can be compressed by different amounts by selecting a position from 1 to 5. This allows the marble to be launched at different speeds. The students set the launch angle to 30.0° and compressed the spring to position 1. The marble was launched, and its initial speed was measured to be 5.60 m s–1. The landing height was the same as the launch height.

(a) (i) Show that the magnitude of the horizontal component of the initial velocity is 4.85 m s–1, and that the magnitude of the vertical component of the initial velocity is 2.80 m s–1.

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(ii) Determine the time of flight for the marble. Ignore air resistance.

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(iii) Calculate the horizontal range of the marble. Ignore air resistance.

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page 4 of 16 Credit will be given for answers to part (b) that are coherent and contain only relevant information. (2 marks)

(b) The students decide to adjust the projectile launcher to increase the range of the marble. Describe two adjustments that the students could make, and explain how each adjustment would increase the range of the marble.

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page 5 of 16 PLEASE TURN OVER 15. A student used a spectrometer (similar to the one shown below) and a diffraction grating to determine the distance between the slits on the diffraction grating.

The student used a light source with a wavelength of 589 nm and measured the angle  of each principal maximum. The student calculated VLQT for each of the measured angles and used a spreadsheet to graph VLQT against the order of the maxima. The graph is shown below.

line of best fit 1.0 0.9 0.8 0.7 0.6

T

n 0.5 i s 0.4 0.3 0.2 0.1 0 0 1 2 3 4 5 6 Order of maxima

The equation of the line of best fit is y  0.18x  6.0  10–16.

page 6 of 16 Using the gradient of the line of best fit, determine the number of slits per metre on the diffraction grating.

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page 7 of 16 PLEASE TURN OVER 16. (a) An experiment was performed in which light of different frequencies f was incident on a metal surface. Electrons were emitted through the photoelectric effect, and their maximum kinetic energies were measured. The data obtained are shown on the graph below.

2.5

2.0

1.5

1.0

(eV)

(max)

K K

K 0.5

E E

0 1.010... 2.2.0...03 3..0...04 4..0.0 5.5.0...06 6..007 7..0...08 8..0.9..09 9..001 100 f (u 1014 Hz) –0.5

–1.0

Determine the work function of the metal surface. Give your answer in electronvolts.

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(b) Scientists are investigating a new environmentally friendly way to generate electricity. This will require a material with a very low work function. One new material has been engineered to have a work function of 0.80 eV. On the graph above, draw a line to show the relationship between the maximum kinetic energy of the electrons emitted from this new material and the frequency of incident light. (2 marks)

page 8 of 16 17. To detect vehicles, a rectangular conducting loop is embedded in a road surface. A varying current in the loop produces a changing magnetic flux. When a vehicle is above the loop, eddy currents are produced on the metal underside of the vehicle. Using Lenz’s Law, explain the production of the eddy currents.

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page 9 of 16 PLEASE TURN OVER 18. Particle accelerators can be used to accelerate protons to very high speeds.

(a) In one particle accelerator, protons pass through a potential difference of 6.3  103 V.

(i) Using Emv   and the law of conservation of energy, show that the protons are K  accelerated to a speed of 1.1  106 m s–1.

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(ii) Show that the momentum of the protons is 1.8  10–21 kg m s–1 after this acceleration.

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(iii) Show that the relativistic effects on this momentum are negligible.

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page 10 of 16 (b) The Large Hadron Collider can cause protons to reach a relativistic speed of 0.99991c. Determine the momentum of a proton travelling at this speed.

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page 11 of 16 PLEASE TURN OVER 19. In 2018 a satellite named Transiting Exoplanet Survey Satellite (TESS) was launched. The satellite travels in an elliptical orbit around the Earth.

(a) The diagram below shows an elliptical orbit.

Earth

Using Kepler’s Second Law of Planetary Motion, explain why a satellite in an elliptical orbit travels faster when it is closer to the Earth.

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page 12 of 16 (b) Transiting Exoplanet Survey Satellite (TESS) was launched by the private company SpaceX. Scientists use the cameras on the satellite to search for and understand exoplanets — planets outside our solar system. The wide-field cameras and detectors aboard TESS are capable of searching more of the sky than any previous technology is. TESS will monitor over 200 000 nearby bright stars and identify planets that are much smaller than those that can be detected by ground-based technologies. Partly due to the presence of liquid water, the Earth is the only planet known to be able to support life. Another satellite to be launched in 2021 will examine the atmosphere of exoplanets identified by TESS for evidence of liquid water. TESS has found types of planets that were not predicted to exist: massive planets orbiting very close to their stars, and planets approximately three times the size of the Earth. Other unexpected discoveries include planets in binary star systems and planets orbiting dead stars. The TESS project involves partnerships between the United States National Aeronautics and Space Administration (NASA), the Massachusetts Institute of Technology, the Space Telescope Science Institute, and the aerospace manufacturing company Orbital ATK. Many universities, research institutes, and individual astronomers will be able to use data from TESS for their own research.

Using the information above, describe three examples of how the Transiting Exoplanet Survey Satellite (TESS) project demonstrates science as a human endeavour.

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page 13 of 16 PLEASE TURN OVER 20. When two protons travelling at high speeds collide, they undergo a reaction. In one possible reaction, shown below, the products are a proton, a neutron, and a kaon particle.

p  p p  n  K

(a) Complete the following table:

Reactants Products pppnK

Baryon number 111

Charge (e) (2 marks)

(b) Before they collided, the protons were travelling in opposite directions with momenta of equal magnitude. Following the reaction, the proton and the neutron each have a momentum of 3.0  10–18 kg m s–1 in the directions shown on the diagram below.

p n

Using the law of conservation of momentum, determine the magnitude of the momentum of the kaon particle produced in the reaction.

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page 14 of 16 (c) The kaon particle produced in the reaction is travelling at a very high speed. In its moving frame of reference it can travel for a time of 1.23  10–8 s, and a distance of 3.68 m, before decaying. However, scientists can detect kaon particles more than 50 m from the collisions that produce them. Explain why it is possible for kaon particles to travel more than 50 m and be detected by scientists.

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page 15 of 16 PLEASE TURN OVER You may write on this page if you need more space to finish your answers to any of the questions in this question booklet. Make sure to label each answer carefully (e.g. 19(b) continued).

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page 16 of 16 — end of question booklet PHYSICS 2018

ACKNOWLEDGMENT

Question 5, photo: Adapted from Nehrener, D 2006, ‘File: Wingletdetail.jpg’, Wikimedia Commons, the free media repository, https://commons.wikimedia.org/w/index.php?title=File:Wingletdetail.jpg&oldid=231922076

The SACE Board of South Australia has made every effort to trace copyright holders. If however, any material has been incorrectly acknowledged, we apologise and invite the copyright holder to contact us.