National Examinations Board Grade 12 Physics — Model Question 2079 (2023)

National Examinations Board · Physics (Grade 12) · 2079 (2023) BS · Model Question — 22 questions — a free old question paper on Goodone.club’s exam-paper archive.

  1. The product of moment of inertia and angular velocity gives (A) force (B) torque (C) linear momentum (D) angular momentum [1 marks]
  2. (i) Define simple harmonic motion. [1] (ii) Derive an expression for the time period of oscillation for a mass m attached to a vertical spring of force constant k. [3] (iii) What will be the time period of this system if it is taken inside a satellite? [1] [5 marks]
  3. (a) What is the significance of the negative energy of the electron in an orbit? [1] (b) The energy levels of an atom are shown in the figure. Which one of these transitions will result in the emission of a photon of wavelength 275 nm? Explain with calculation. (h = 6.64×10⁻³⁴ Js, c = 3.0×10⁸ ms⁻¹) [3] (c) Find the expression for the wavelength of radiation emitted from a hydrogen atom when an electron jumps from a higher energy level n₂ to a lower energy level n₁. [2] (d) Calculate the magnitude of the wavelength of the second line of the Balmer series. (R = 1.09×10⁷ m⁻¹) [2] [8 marks]
  4. The bob of a simple pendulum has a mass of 0.40 kg. The pendulum oscillates with a period of 2.0 s and an amplitude of 0.15 m. At an extreme point in its cycle, it has a potential energy of 0.044 J. What is the kinetic energy of the pendulum bob at its mean point? (A) 0.022 J (B) 0.044 J (C) 0.011 J (D) 0.033 J [1 marks]
  5. (a) State Bernoulli's principle. [1] (b) The figure shows a liquid of density 1200 kg m⁻³ flowing steadily in a tube of varying cross-sections. The cross-section at point A is 1.0 cm² and that at B is 20 mm²; points A and B are in the same horizontal plane. The speed of the liquid at A is 10 cm/s. Calculate: (i) the speed at B. [2] (ii) the difference in pressure at A and B. [2] [5 marks]
  6. (a) A student is measuring the wavelength of green light from a mercury lamp (λ = 546 nm). Using a double slit of separation 0.50 mm, he sees ten clear fringes on a screen 0.80 m from the slits. He then uses a diffraction grating of 3000 lines/cm. (i) What is the width of the ten fringes in the first experiment? [2] (ii) What is the angle of the second-order maximum in the second experiment? [2] (iii) Suggest which experiment gives the more accurate measurement of wavelength. [1] (b) In what way can one differentiate between polaroid and non-polaroid sunglasses? [1] (c) At what angle of incide... [8 marks]
  7. What causes earthquakes? (A) The flow of magma (B) The expansion of the earth's crust (C) The rubbing together of earth's plates (D) Tsunami [1 marks]
  8. (a) Draw a PV diagram of a petrol engine and explain its working based on its PV diagram. [3] (b) Compare the efficiency of a petrol engine with that of a diesel engine based on their compression ratios. [2] [5 marks]
  9. (a) What is a choke coil? [1] (b) For the given a.c. circuits: (i) If the frequency of the e.m.f. is increased, what will be the effect on the currents flowing in them? Explain. [3] (ii) What difference do you expect in the opposition provided by the circuits for current flow in figures (a) and (b) if the given a.c. e.m.f. is replaced by its equivalent d.c. e.m.f.? [2] (c) Explain the working of the circuit. [2] OR (a) Define 1 ampere of current in terms of the force between two parallel current-carrying conductors. [1] (b) How do you explain the contraction of a solenoidal coil while current... [8 marks]
  10. What percentage of original radioactive atoms is left after 4 half-lives? (A) 1% (B) 6% (C) 10% (D) 20% [1 marks]
  11. (a) When the wire of a sonometer is 75 cm long, it is in resonance with a tuning fork. On shortening the wire by 0.5 cm it makes 3 beats with the same fork (the beat is the difference in frequencies). Calculate the frequency of the tuning fork. [3] (b) In an experiment to measure the speed of sound in a string, the frequency of the vibrator is adjusted until a standing wave is formed. The frequency of the vibrator is 120 Hz. Calculate the speed at which a progressive wave would travel along the string. [2] [5 marks]
  12. Two wave pulses travel toward each other as shown in the diagram. Which of the following diagrams represents the superposition of the pulses when they meet? [1 marks]
  13. (a) State Lenz's law in electromagnetism. Justify that this law is in favour of the principle of conservation of energy. [1+2=3] (b) A magnet is quickly moved in the direction indicated by an arrow between two coils C₁ and C₂. What will be the direction of the induced current in each coil? Explain. [2] [5 marks]
  14. Which one of the following properties of sound is affected by the change in air temperature? (A) amplitude (B) frequency (C) wavelength (D) intensity [1 marks]
  15. (a) State the principle of the potentiometer. A potentiometer is also called a voltmeter of infinite resistance — why? [1+1=2] (b) In the meter bridge experiment, the balance point was observed at J with l = 20 cm. (i) The values of R and X were doubled and then interchanged. What would be the new position of the balance point? [2] (ii) If the galvanometer and battery are interchanged at the balance position, how will the balance point be affected? [1] OR (a) State the two Kirchhoff's laws for electrical circuits. [2] (b) In a meter bridge, the null point is found at 60.0 cm from A. If now a r... [5 marks]
  16. Internal energy of an ideal gas depends on (A) volume only (B) pressure only (C) temperature only (D) both pressure and volume [1 marks]
  17. The graph shows the maximum kinetic energy of the emitted photoelectrons as the frequency of the incident radiation on a sodium plate is varied. (a) From the graph, determine the maximum frequency of incident radiation that can cause a photoelectric effect. [1] (b) Calculate the work function for sodium. [2] (c) Use the graph to calculate the value of the Planck constant in Js. [2] [5 marks]
  18. In which of the following processes of the gas, work done is the maximum? (A) Isothermal (B) Isobaric (C) adiabatic (D) Isochoric [1 marks]
  19. (a) The figure shows the experimental setup of Millikan's oil-drop experiment. Find the expression for the charge of an oil drop of radius r moving with constant velocity v in a downward direction using a free-body diagram. [2] (b) What will be the expression for the charge of an oil drop if the electric force is greater than its weight? [1] (c) Determine the electric field supplied when the electric force applied between the two horizontal plates just balances an oil drop with 4 electrons attached to it, given the mass of the oil drop is 1.3×10⁻¹⁴ kg. [2] OR (a) A diode can be used as a recti... [5 marks]
  20. The neutral temperature of a thermocouple is equal to 500°C when the temperature of cold junction is 0°C. Percentage change in the temperature of inversion when temperature of cold junction is equal to 20°C is (A) 2% (B) 3% (C) 4% (D) 5% [1 marks]
  21. In which of the following circuits the maximum power dissipation is observed? (A) a circuit having inductor and resistor in series (B) pure resistive circuit (C) pure inductive circuit (D) pure capacitive circuit [1 marks]
  22. Why are laminated cores placed in transformers? (A) to reduce hysteresis loss (B) to reduce eddy current (C) to reduce the magnetic effect (D) to increase coercivity [1 marks]