OCR A-Level Physics 2027 Predicted Practice Paper — Unified Physics

Answer ALL questions. Write your answers in the spaces provided. You must write down all the stages in your working.

Section A

Synoptic and practical-based questions. Answer ALL the questions.

• 1

  Question SECTION-A1 (6 marks)

  A student investigates the discharge of a capacitor through a fixed resistor. A 4700 microfarad capacitor is charged to 9.0 V and then discharged through a 22 kilo-ohm resistor. (a) Calculate the time constant of the circuit and state what it represents physically. (b) Calculate the potential difference across the capacitor 60 s after discharge begins. (c) The student wishes to determine the time constant experimentally by plotting a straight-line graph. State what quantities should be plotted on each axis, and explain how the time constant is obtained from the graph.

  (Total for Question SECTION-A1 is 6 marks)
• 2

  Question SECTION-A2 (7 marks)

  A satellite of mass 1200 kg orbits the Earth in a circular geostationary orbit. Take G = 6.67e-11 N m^2 kg^-2 and the mass of the Earth M = 5.97e24 kg. (a) State the two conditions that define a geostationary orbit. (b) Show that the orbital radius of a geostationary satellite is approximately 4.2e7 m. (c) Calculate the gravitational potential energy of the satellite in this orbit.

  (Total for Question SECTION-A2 is 7 marks)
• 3

  Question SECTION-A3 (6 marks)

  A mass-spring system consists of a 0.25 kg mass on a spring of spring constant 40 N m^-1, oscillating vertically with simple harmonic motion of amplitude 0.080 m. (a) Calculate the period of oscillation. (b) Calculate the maximum speed of the mass. (c) Sketch and describe how the kinetic energy and potential energy of the system vary with displacement over one complete oscillation.

  (Total for Question SECTION-A3 is 6 marks)
• 4

  Question SECTION-A4 (6 marks)

  In a nuclear physics experiment, the binding energy per nucleon of iron-56 is 8.79 MeV and that of helium-4 is 7.07 MeV. (a) Explain what is meant by binding energy per nucleon. (b) Explain, with reference to the binding energy per nucleon curve, why energy is released in both nuclear fusion of light nuclei and nuclear fission of heavy nuclei. (c) Calculate the total binding energy of a helium-4 nucleus in joules. (1 MeV = 1.60e-13 J.)

  (Total for Question SECTION-A4 is 6 marks)
• 5

  Question SECTION-A5 (5 marks)

  A student uses a search coil connected to a data logger to investigate electromagnetic induction. A bar magnet is dropped so it falls vertically through a horizontal circular coil of 240 turns and cross-sectional area 1.5e-3 m^2. (a) State Faraday's law and Lenz's law. (b) As the magnet approaches the coil, the average rate of change of magnetic flux density through the coil is 0.85 T s^-1. Calculate the magnitude of the average induced e.m.f. (c) Explain why the induced e.m.f. is greater as the magnet leaves the coil than as it enters.

  (Total for Question SECTION-A5 is 5 marks)
• 6

  Question SECTION-A6 (5 marks)

  An ideal gas is contained in a sealed cylinder of fixed volume 2.0e-3 m^3. The gas contains 0.15 mol of molecules at a temperature of 27 degrees C. Take R = 8.31 J mol^-1 K^-1 and the Boltzmann constant k = 1.38e-23 J K^-1. (a) Calculate the pressure of the gas. (b) Calculate the mean (average) translational kinetic energy of a single gas molecule. (c) The gas is heated so that its absolute temperature doubles. State and explain the effect on the root-mean-square speed of the molecules.

  (Total for Question SECTION-A6 is 5 marks)
• 7

  Question SECTION-A7 (6 marks)

  A student measures the resistivity of a metal wire. The wire has a measured length of 1.500 m (+/- 0.001 m), a diameter measured with a micrometer as 0.38 mm (+/- 0.01 mm), and a resistance measured as 2.85 ohm (+/- 0.05 ohm). (a) Calculate the resistivity of the metal. (b) Determine the percentage uncertainty in the calculated value of resistivity. (c) State which single measurement contributes most to the overall uncertainty, and suggest one improvement to reduce it.

  (Total for Question SECTION-A7 is 6 marks)

Section B

Extended response and synoptic questions. Answer ALL the questions.

• 1

  Question SECTION-B1 (10 marks)

  A capacitor is used in a camera flash circuit. A 220 microfarad capacitor is charged through a 15 kilo-ohm resistor from a 6.0 V supply, then rapidly discharged through the flash lamp. (a) Calculate the energy stored on the capacitor when fully charged to 6.0 V. (b) Calculate the maximum charging current at the instant charging begins. (c) The flash lamp fully discharges the capacitor in 4.0 ms. Estimate the average power delivered to the lamp during the flash. (d) The designer replaces the capacitor with one of larger capacitance but keeps the same charging resistor and supply. Discuss the effects this has on (i) the maximum energy stored, (ii) the time taken to charge the capacitor, and (iii) the peak brightness and duration of the flash.

  (Total for Question SECTION-B1 is 10 marks)
• 2

  Question SECTION-B2 (10 marks)

  This question compares gravitational and electric fields. (a) State two similarities and two differences between gravitational fields and electric fields. (b) An alpha particle (charge +2e, mass 6.64e-27 kg) is fired directly towards a stationary gold nucleus (charge +79e) from far away with an initial kinetic energy of 8.0 MeV. Take e = 1.60e-19 C, 1/(4 pi epsilon_0) = 8.99e9 N m^2 C^-2, and 1 MeV = 1.60e-13 J. Calculate the closest distance of approach, assuming the gold nucleus remains stationary. (c) Explain why the actual closest approach would differ slightly from your calculated value if the gold nucleus were free to recoil. (d) Sketch a graph showing how the electric potential energy of the alpha particle varies with its distance from the nucleus as it approaches and then recoils.

  (Total for Question SECTION-B2 is 10 marks)
• 3

  Question SECTION-B3 (9 marks)

  Radioactive decay and its applications. A sample of the radioisotope sodium-24 is used as a medical tracer. Sodium-24 has a half-life of 15.0 hours and decays by beta-minus emission. The initial activity of the sample is 2.4e6 Bq. (a) Define the decay constant and calculate its value for sodium-24 in s^-1. (b) Calculate the number of sodium-24 nuclei present in the sample initially. (c) Calculate the activity of the sample after 40 hours. (d) Explain why a beta-emitting isotope with a half-life of several hours is suitable as a medical tracer, referring to both the type of radiation and the half-life.

  (Total for Question SECTION-B3 is 9 marks)