2022, Prova 1

QUESTION 1 Electromotive force is (A) the production of voltage across an electrical conductor due to its dynamic interaction with a magnetic field. (B) a difference in potential that tends to give rise to an electric current. (C) the repulsion experienced by two negatively charged particles. (D) one of the four fundamental forces.

QUESTION 2 A photon is described as (A) a continuous wave of light energy. (B) a particle that can only propagate in a medium. (C) a quantum of all forms of electromagnetic energy. (D) a particle that mediates the forces between protons.

QUESTION 3 Which free body diagram best represents an object being pulled at a constant speed up an inclined plane? (A) FN FT Ff Fg (B) Ff FN Fg FT (C) FT FN Fg Ff (D) Ff FT Fg FN

QUESTION 4 An object orbiting Earth has an orbital period of 5.6 × 103 s. What is the object’s orbital radius? (A) 3.8 × 105 m (B) 6.8 × 106 m (C) 1.8 × 1010 m (D) 1.3 × 1012 m

QUESTION 5 Tau particles are classified as (A) bosons. (B) leptons. (C) mesons. (D) baryons.

QUESTION 6 After coherent light has been passed through a double slit, the observation of an interference pattern on a screen is explained by the (A) wave nature of light. (B) equal width of the slits. (C) discrete packets of photons. (D) distance from the slits to the screen.

QUESTION 7 Which change would produce the greatest increase in magnetic field strength inside a current-carrying solenoid? (A) decreasing the thickness of the wire (B) increasing the length of the solenoid (C) adding more turns of wire to the solenoid (D) using an alternating current instead of a direct current

QUESTION 8 Determine the wavelength of an electromagnetic wave with an energy of 2.4 × 10−23 J. (A) 7.2 × 10−15 m (B) 2.8 × 10−11 m (C) 8.3 × 10−3 m (D) 1.2 × 102 m

QUESTION 9 Which diagram would result in the furthest horizontal distance travelled? (A) v = 12 m s−1 20° (B) v = 11 m s−1 45° (C) v = 10 m s−1 20° (D) v = 9 m s−1 45° Not to scale

QUESTION 10 Electric field strength refers to the (A) intensity of an electric field at a particular location. (B) change in electrical potential energy between two defined points. (C) sum of electrically charged particles passing a point in a given time. (D) physical property of an object experiencing a force in an electromagnetic field.

QUESTION 11 The maximum kinetic energy of an electron ejected from a metallic surface can be increased by (A) using a positively ionised metal. (B) using a metal with a larger work function. (C) increasing the intensity of the incident light. (D) decreasing the wavelength of the incident light.

QUESTION 12 An object experiencing uniform circular motion in a horizontal plane travels at an average speed of 8.0 m s−1. Calculate the radius of the object’s path if it takes 0.3 s to complete a full rotation. (A) 3.8 × 10−1 m (B) 2.6 × 100 m (C) 1.5 × 101 m (D) 1.7 × 102 m

QUESTION 13 A rectangular coil of 3000 turns and dimensions 0.1 m × 0.2 m is rotated in a uniform magnetic field of 2 mT. Calculate the minimum number of revolutions per second required to produce an average EMF of 6 V. (A) 1 (B) 3 (C) 13 (D) 50

QUESTION 14 Which Feynman diagram correctly depicts neutron decay? (A) Space Time u d d u d d e− W+ veˇ (B) Space Time e− W+ veˇ d u u d u d (C) Space Time e− W− veˇ u d d u u d (D) Space W− veˇ u d d u d d

QUESTION 15 An object’s velocity can only be measured relative to (A) a fixed reference frame. (B) the speed of light. (C) an object at rest. (D) an observer.

QUESTION 16 Two vectors are shown. 40.0° 60.0° X = 35 Y = 48 Which option represents the resultant vector of X + Y? (A) 51.6° 81.8 (B) 43.4° 69.9 (C) 36.1° 59.4 (D) 20.6° 54.3 Not to scale

QUESTION 17 An object is in orbit 400 km above the surface of the Earth. The Earth has a radius of 6.4 × 106 m. What is the magnitude of the gravitational field strength experienced by the object? (A) 8.6 × 100 m s−2 (B) 9.7 × 100 m s−2 (C) 2.5 × 103 m s−2 (D) 5.9 × 107 m s−2

QUESTION 18 The primary and secondary coils from a lossless transformer are shown. Secondary Primary Compared to the primary coil, the secondary coil will experience decreased (A) power. (B) current. (C) voltage. (D) resistance.

QUESTION 19 A current-carrying wire is placed perpendicular to two magnets. As the current in the wire is changed, the force acting on it is recorded. Current (A) Force (10−5 N) 0 0.2 0.4 0.6 0.8 1.0 6 3 2 1 0 5 4 The gradient of the line of best fit is proportional to the (A) potential difference. (B) electromotive force. (C) resistance of the wire. (D) magnetic field strength.

QUESTION 20 Which option lists the gauge bosons in ascending order of the strength of force they mediate? (A) W boson < Z boson < Photon (B) Gluon < Z boson < W boson (C) Photon < W boson < Gluon (D) Z boson < Photon < Gluon

QUESTION 21 (2 marks) A hot iron bar was observed to have a deep red colour. As the iron bar was heated further, the colour changed to orange. Explain the observed colour change in terms of black-body radiation.

QUESTION 22 (2 marks) A collection of mesons was observed by a detector to move an average distance of 11.0 m when travelling at 95% of the speed of light. However, based on their properties, the mesons were expected to travel an average distance of 3.4 m. Explain the difference between the observed and expected average distances.

QUESTION 23 (6 marks) The diagram shows the electron energy levels for hydrogen. n = 6 −0.38 eV n = 5 −0.54 eV n = 4 −0.85 eV n = 3 −1.51 eV n = 2 −3.40 eV n = 1 −13.60 eV Ionisation Ground level a) Calculate the energy released, in joules, when an electron moves from the third to the first energy level. Show your working. [3 marks] Energy released = J (to three significant figures) The visible light emission spectrum for hydrogen is shown. 410 434 486 656 Wavelength (nm) b) Explain why hydrogen only has four emission spectrum lines in the visible (i.e. 400–700 nm) spectrum. [3 marks]

QUESTION 24 (3 marks) A rectangular loop is placed in a uniform magnetic field of 5 mT. N S 20 cm 30 cm Not to scale Calculate the change in flux through the loop when it is rotated 60° around the vertical axis. Show your working. Change in flux = Wb (to two significant figures)

QUESTION 25 (2 marks) Describe how electromagnetic radiation is propagated by the interaction between electric and magnetic fields.

QUESTION 26 (1 mark) Carbon-14 undergoes nuclear decay to nitrogen-14. 14 14 6 7 − → + + e C N e v List the two types of particles whose total number must be conserved in this reaction.

QUESTION 27 (5 marks) Object A is five times the mass of object B. The graph shows the contribution of each object towards the strength of the net gravitational field between them. 10 1 0.1 0.01 0.001 0.0001 0.00001 10 20 30 40 0 Distance from the centre of A (107 m) Gravitational field strength (m s−2) A B Determine the total distance between the centre of the two objects. Show your working. Total distance = m (to two significant figures)

QUESTION 28 (7 marks) An object of mass 200 g moves in a uniform circular path with a radius of 25 cm. The time taken for 10 revolutions is 3.0 s. a) Calculate the distance travelled by the object after 3.9 s. Show your working. [2 marks] Distance = m (to two significant figures) b) Calculate the centripetal force acting on the object. Show your working. [5 marks] Centripetal force = N (to two significant figures)