Laws of Equilibrium - Physics - Exam Paper, Exams of Physics

Download Laws of Equilibrium - Physics - Exam Paper and more Exams Physics in PDF only on Docsity! LEAVING CERTIFICATE EXAMINATION 2007: PHYSICS – HIGHER LEVEL 2007 Question 1 A student investigated the laws of equilibrium for a set of co-planar forces acting on a metre stick. The student found that the centre of gravity of the metre stick was at the 50.4 cm mark and its weight was 1.2 N. (i) How did the student find the centre of gravity? (ii) How did the student find the weight, of the metre stick? (iii) Why is the centre of gravity of the metre stick not at the 50.0 cm mark? (iv) The student applied vertical forces to the metre stick and adjusted them until the metre stick was in equilibrium. How did the student know that the metre stick was in equilibrium? The student recorded the following data. (v) Calculate the net force acting on the metre stick. (vi) Calculate the total clockwise moment about a vertical axis of the metre stick. (vii) Calculate the total anti-clockwise moment about a vertical axis of the metre stick. (viii) Use these results to verify the laws of equilibrium. 2007 Question 2 The specific heat capacity of water was found by adding hot copper to water in a copper calorimeter. The following data was recorded. (i) Describe how the copper was heated and how its temperature was measured. (ii) Using the data, calculate the energy lost by the hot copper. (iii) Using the data, calculate the specific heat capacity of water. (iv) Give two precautions that were taken to minimise heat loss to the surroundings. (v) Explain why adding a larger mass of copper would improve the accuracy of the experiment. (specific heat capacity of copper = 390 J kg–1 K–1) 2007 Question 3 In an experiment to measure the focal length of a concave mirror, an approximate value for the focal length was found. The image distance v was then found for a range of values of the object distance u. The following data was recorded. u/cm 15.0 20.0 25.0 30.0 35.0 40.0 v/cm 60.5 30.0 23.0 20.5 18.0 16.5 (i) How was an approximate value for the focal length found? (ii) What was the advantage of finding the approximate value for the focal length? (iii) Describe, with the aid of a labelled diagram, how the position of the image was found. (iv) Calculate the focal length of the concave mirror by drawing a suitable graph based on the recorded data. 2007 Question 4 The following is part of a student’s report of an experiment to investigate of the variation of current I with potential difference V for a semiconductor diode. I put the diode in forward bias as shown in the circuit diagram. I increased the potential difference across the diode until a current flowed. I measured the current flowing for different values of the potential difference. I recorded the following data. (i) Draw a circuit diagram used by the student. (ii) How did the student vary and measure the potential difference? (iii) Draw a graph to show how the current varies with the potential difference. (iv) Estimate from your graph the junction voltage of the diode. (v) The student then put the diode in reverse bias and repeated the experiment. What changes did the student make to the initial circuit? position on metre stick/cm 11.5 26.2 38.3 70.4 80.2 magnitude of force/N 2.0 4.5 3.0 5.7 4.0 direction of force down up down up down mass of calorimeter 55.7 g mass of calorimeter + water 101.2 g mass of copper + calorimeter + water 131.4 g initial temperature of water 16.5 oC temperature of hot copper 99.5 oC final temperature of water 21.0 oC V/V 0.60 0.64 0.68 0.72 0.76 0.80 I /mA 2 4 10 18 35 120 (vi) Draw a sketch of the graph obtained for the diode in reverse bias. 2007 Question 5 (a) State Archimedes’ principle. (b) Why is a filament light bulb not an efficient source of light? (c) Why does the temperature of an athlete reduce when she perspires? (d) How is infra-red radiation detected? (e) The refractive index of a liquid is 1.35, what is the critical angle of the liquid? (f) Calculate the energy stored in a 5 μF capacitor when a potential difference of 20 V is applied to it. (g) Why does a magnet that is free to rotate point towards the North? (h) State the principle on which the definition of the ampere is based. (i) How are electrons accelerated in a cathode ray tube? (j) A kaon consists of a strange quark and an up anti-quark. What type of hadron is a kaon? or Draw the basic structure of a bi-polar transistor. 2007 Question 6 (i) State Hooke’s law. (ii) A stretched spring obeys Hooke’s law. When a small sphere of mass 300 g is attached to a spring of length 200 mm, its length increases to 285 mm. Calculate its spring constant. (iii) The sphere is pulled down until the length of the spring is 310 mm. The sphere is then released and oscillates about a fixed point. Derive the relationship between the acceleration of the sphere and its displacement from the fixed point. (iv) Why does the sphere oscillate with simple harmonic motion? (v) Calculate the period of oscillation of the sphere (vi) Calculate the maximum acceleration of the sphere (vii) Calculate the length of the spring when the acceleration of the sphere is zero. (acceleration due to gravity = 9.8 m s–2) 2007 Question 7 (i) What is the Doppler Effect? (ii) Explain, with the aid of labelled diagrams, how this phenomenon occurs. (iii) The emission line spectrum of a star was analysed using the Doppler Effect. Describe how an emission line spectrum is produced. (iv) The red line emitted by a hydrogen discharge tube in the laboratory has a wavelength of 656 nm. The same red line in the hydrogen spectrum of a moving star has a wavelength of 720 nm. Is the star approaching the earth? Justify your answer. (v) Calculate the frequency of the red line in the star’s spectrum. (vi) Calculate the speed of the moving star. (speed of light = 3.00 × 108 m s–1) 2007 Question 8 (i) Define electric field strength and give its unit of measurement. (ii) Describe how an electric field pattern may be demonstrated in the laboratory. (iii) The dome of a Van de Graff generator is charged. The dome has a diameter of 30 cm and its charge is 4 C. A 5 μC point charge is placed 7 cm from the surface of the dome. Calculate the electric field strength at a point 7 cm from the dome (iv) Calculate the electrostatic force exerted on the 5 μC point charge. (v) All the charge resides on the surface of a Van de Graff generator’s dome. Explain why. (vi) Describe an experiment to demonstrate that total charge resides on the outside of a conductor. (vii) Give an application of this effect. (permittivity of free space = 8.9 × 10–12 F m–1)