L.36 PRE-LEAVING CERTIFICATE EXAMINATION, 2015 PHYSICS HIGHER LEVEL TIME 3 HOURS Answer three questions from Section A and five questions from Section B. N.B. Relevant data are listed in the Formulae and Tables booklet, which is available from the Superintendent. 2015.1 L.36 1/12 page 1 of 12
Answer three questions from this section. Each question carries 40 marks. SECTION A (120 marks) 1. In an experiment to measure the acceleration due to gravity g, a student measured the time for a small sphere to fall through a height s. The student repeated the procedure for a series of different values of the height and recorded the following data. s/m 0.4 0.5 0.6 0.7 0.8 0.9 1.0 t/ms 286 320 349 378 405 426 454 Describe, with the aid of a labelled diagram, how the student obtained the data. (12) What is the relationship between s and t for the sphere falling under gravity? Based on this relationship, draw a suitable graph based on the recorded data. (15) = 56.5 g = 131.8 g Use your graph to calculate a value for the acceleration due to gravity, g. (9) State one possible source of error in measuring the distance travelled s or one source of error in measuring the time of fall t. (4) 2. In an experiment to measure the specific latent heat of fusion of ice, ice was added to water in an insulated copper calorimeter. The following measurements were recorded: Mass of copper calorimeter Mass of calorimeter + water Initial temperature of water = 29.4 C Temperature of ice = 0 C Final temperature of water = 11.9 C Mass of calorimeter + water + melted ice = 147.3 g State two procedures used to prepare the ice before adding it to the water, to ensure a more accurate result. Give a reason for each of these procedures. (12) State a method, other than insulating the copper calorimeter, of minimising heat loss in the experiment. (4) Using the recorded data, calculate the specific latent heat of fusion of ice. (18) Why should the final temperature of the water not be allowed to drop to near 0 C? (6) (specific heat capacity of copper = 390 J kg 1 K 1 ; specific heat capacity of water = 4180 J kg 1 K 1 ) 2015.1 L.36 2/12 page 2 of 12
3. A student performed two experiments to investigate the variation of the fundamental frequency of a stretched string with two different factors. In experiment 1, the student measured and recorded the frequency of the stretched string and its corresponding length (in metres), using a range of tuning forks from 256 Hz to 512 Hz. In experiment 2, the student recorded the frequency of the same stretched string and its corresponding tension (in Newtons), using the same range of tuning forks. The following graphs were plotted for each experiment. 2.5 Experiment 1 7 Experiment 2 A Vertical scale 2.0 1.5 1.0 0.5 0 0 100 200 300 400 500 600 f (Hz) 0 Explain, using a labelled diagram, how the frequency, length and tension were measured for each experiment. (12) Label the vertical scales, A and B, in both graphs using suitable quantities and units. (10) Use the graph to estimate the longest length of the stretched string in experiment 1. (9) Given that the mass per unit length of the string is 1.1 10 4 kg m 1, use the graph to estimate the constant length at which the string was maintained in experiment 2. (9) 4. In an experiment to determine the resistivity of nichrome, the following data was collected. B Vertical scale 6 5 4 3 2 1 0 100 200 300 400 500 600 f (Hz) length of the wire resistance of the wire = 70.7 cm = 9.2 Position 1 2 3 4 5 6 Diameter (mm) 0.36 0.37 0.35 0.35 0.34 0.36 zero error reading = 0.03 mm Describe how the data was collected. (15) Using the recorded data, calculate the resistivity of nichrome. (12) Tungsten has very low resistivity and is often used as the filament in a filament bulb. Sketch a graph of current against voltage for the tungsten filament in the bulb. Use your graph to explain how the resistivity varies as the voltage is increased. (13) 2015.1 L.36 3/12 page 3 of 12
Answer five questions from this section. Each question carries 56 marks. SECTION B (280 marks) 5. Answer any eight of the following parts, (a), (b), (c), etc. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) State the conditions necessary for the equilibrium of a body under a set of co-planar forces. A gun of mass 1.5 kg fires a bullet of mass 12 g which exits the gun at 450 m s 1. Calculate the recoil velocity of the gun. Why is there a need to choose a standard thermometer based on one specific thermometric property? Define solar constant. State two adjustments that need to be made to a spectrometer before using it to measure the wavelengths present in a light source. Water gains 365 kj of energy while being heated for 2 minutes in a kettle that is 80% efficient. The element of the kettle has a resistance of 18. Calculate the current flowing in the element of the kettle. A wire of length 70 cm and carrying a current of 2 A experiences a force of 5.4 N in a magnetic field of flux density 6 T. Calculate the angle between the magnetic field and the wire. What is meant by the term self induction? Give two applications of the photoelectric effect. Give the quark composition of a proton and an anti-neutron. or State the principle on which an induction motor is based. (8 7) 2015.1 L.36 4/12 page 4 of 12
6. State Archimedes principle. Describe an experiment that demonstrates Archimedes principle. (18) Explain how the law of flotation relates to Archimedes principle for a floating object. (9) A cube of side 30 cm is placed underwater with the top side parallel to the surface and 20 cm below the surface. Calculate (i) the pressure exerted on the top surface of the cube due to the water (6) (ii) the force exerted on the top surface due to the water (6) (iii) the force exerted on the bottom surface due to the water. (9) 30 cm 20 cm If the mass of the cube is 25 kg, will it sink or float? Explain your answer. (8) (density of water = 1000 kg m 3 ; acceleration due to gravity, g = 9.8 m s 2 ) 7. In the 1920s, an English postgraduate student, Cecelia Payne, proposed that the spectra observed from the Sun were not of iron but were mostly hydrogen and also helium. Though initially there was widespread opposition to Payne s results, it was eventually accepted that hers was the correct interpretation. Explain how an emission line spectrum is produced from a sample of hydrogen or helium gas. (12) What is the name of the reaction in which helium is produced in the Sun? Explain how this reaction occurs. Include a possible equation for this reaction in your answer. (15) When looking at a distant star (containing the same gases as those of the Sun), it was found that the lines of the spectrum were slightly shifted from those of the spectrum of the Sun. The observed wavelength of one helium line from the Sun s spectrum was measured as 587 nm and the corresponding line from the spectrum of the distant star was measured as 591 nm. The wavelength of one hydrogen line observed from the Sun s spectrum was measured as 695 nm. A corresponding line from the spectrum of the distant star was observed and its wavelength was measured. Is the distant star moving towards or away from the Earth? Explain your answer. (6) What is the speed at which the star is moving in relation to the Earth? (14) What is the wavelength of the corresponding hydrogen line from the distant star? (9) 2015.1 L.36 5/12 page 5 of 12
8. Computers today have integrated circuits that contain millions of components such as transistors, diodes, resistors and capacitors. Transistors can be made from p-type and n-type silicon semiconductor materials. Explain how p-type and n-type silicon semiconductors can be produced. What is the benefit of using p-type and n-type silicon semiconductors instead of intrinsic semiconductors? (15) A semiconductor diode is a device that allows current to flow through it in one direction only. Explain, using diagrams, how p-type and n-type semiconductors are used to achieve this function in (i) forward bias and (ii) reverse bias. (18) One application of a diode is rectification of a.c. electricity. Explain the underlined term. (6) An oscilloscope is connected across the resistor in the circuit shown below. V R oscilloscope DEB Exams Sketch the graph that would be observed on the oscilloscope. If the peak voltage of the a.c. supply is 75 V and this produces a peak current of 0.8 A, what is the energy dissipated from the resistor in 10 seconds? (17) 9. X-rays have a wide range of applications: from taking X-ray photographs and removing cancerous cells within medicine to detecting flaws and thicknesses of objects in industry. What are X-rays? Name the scientist who discovered them. (9) Name two energy conversions that take place in an X-ray tube. State where each energy conversion occurs within the X-ray tube. (12) Draw a labelled diagram of an X-ray tube. (12) X-rays of maximum wavelength 2 10 11 m are required in an X-ray tube. (i) Calculate the minimum kinetic energy of the electrons in the X-ray tube. (ii) Calculate the minimum voltage needed across the X-ray tube. (14) Why would the voltage across a cathode ray tube be much less than that of an X-ray tube? (6) Give a reason why it may be better to use X-rays rather than gamma-rays in detecting flaws in thin pipes. (3) 2015.1 L.36 6/12 page 6 of 12
10. Answer either part (a) or part (b). (a) There are two main types of circular particle accelerators: cyclotrons and synchrotrons. Cyclotrons are normally used in small-scale projects. They involve the charged particle starting from the centre of a cylinder or sphere and accelerating outwards in a spiral. Synchrotrons are normally used in large projects such as the Large Hadron Collider (LHC) at CERN. They involve the particles being accelerated in a fixed circle called a torus. How are particles accelerated in cyclotron or synchrotron accelerators? (6) A proton is a suitable baryon for use as the accelerating particle in a particle accelerator. Name two baryons that could not be used as accelerating particles in a particle accelerator and explain why they could not be used. (12) The accelerator complex at CERN is a succession of machines that accelerate particles to increasingly higher energies, starting with the Linac 2 (which accelerates particles to 50 MeV). The beam is then injected into the proton synchrotron booster (PSB) (particles accelerated to 1.4 GeV), followed by the proton synchrotron (PS) (particles accelerated to 25 GeV). They are then sent to the super proton synchrotron (SPS) (particles accelerated to 450 GeV) and finish with the LHC (which accelerates particles to 4 TeV). What is the maximum speed of a proton in the Linac 2 accelerator? (9) What is the mass of the largest particle that could be produced in the PSB accelerator if two protons collided travelling in opposite directions? (9) Identify the lowest-energy particle accelerator in CERN that could result in a detector in that accelerator observing the presence of a + meson following two protons colliding. (11) In July 2012, scientists at CERN announced that they detected uncharged particles from detectors on the LHC, of mass 2.22 10 25 kg, which were consistent with the model of the Higgs Boson. What is the maximum number of these particles that could have been produced in one collision of two protons in the LHC accelerator? (9) 2015.1 L.36 7/12 page 7 of 12
(b) A solenoid is a type of coil of wire that is widely used in different electrical applications. The name solenoid was introduced by André-Marie Ampère and means pipe shape. Sketch the magnetic field due to a current in a solenoid. Show the direction of the current in your answer. State two ways by which the strength of the magnetic field around a solenoid could be increased. (12) Solenoids are used in electromagnetic relays to start motors in a car. Draw a circuit for an electromagnetic relay that could be used to start a car motor. Why are wires of two different thicknesses used in different parts of the circuit? (19) The moving-coil loudspeaker also includes a solenoid or coil. Explain, using a diagram, how a moving-coil loudspeaker converts an a.c. signal into an audible sound. (15) An induction coil uses two solenoids, called the primary and secondary coils. State two differences in the structures of primary and secondary coils. Give a reason for each of these differences. (10) 2015.1 L.36 8/12 page 8 of 12
11. Read the following passage and answer the accompanying questions. LASIK is eye surgery that permanently changes the shape of the cornea (the clear covering on the front of the eye) in order to improve vision and reduce a person s dependency on glasses or contact lenses. For clear vision, the eye s cornea and lens must bend (refract) light rays properly, so that images are focused clearly on the retina. Otherwise, the images will be blurry. This blurriness is referred to as a refractive error. It is caused by a difference between the shape of the cornea (curvature) and the length of the eye. LASIK uses an excimer laser (an ultraviolet laser) to precisely remove corneal tissue, giving it a new shape so that light rays are focused clearly on the retina. LASIK causes the cornea to be thinner. LASIK is an outpatient surgical procedure. It will take 10 to 15 minutes to perform for each eye. The only anaesthetic used is eye drops that numb the surface of the eye. The procedure is done when you are awake, but you will get medicine to help you relax. LASIK may be done on one or both eyes during the same session. LASIK involves creating a flap of corneal tissue which is then peeled back so that the excimer laser can reshape the corneal tissue underneath. The amount of tissue the laser will remove is calculated ahead of time. Once the reshaping is done, the surgeon replaces and secures the flap. No stitches are needed. The cornea will naturally hold the flap in place. (i) (ii) (Adapted from MedlinePlus LASIK Eye Surgery) The lens is based on the principle of refraction of light. Explain the underlined term. Without having laser eye surgery, how does the eye adjust to ensure sharp images are focused on the retina from a particular distance? (iii) How does making the thickness of the cornea thinner during laser eye surgery help to improve sight when viewing distant objects? (iv) If the distance between the lens system in an eye and the retina in 2 cm, what is the power of the lens system when light from a distant object is focused on the retina? (v) If the cornea acts as a lens with a power of 40 m 1, what is the focal length of the variable lens when the lens system focuses on a distant object? (vi) If the nearest distance from the eye that an object can be placed and still be in focus is 10 cm, what is the maximum power of the variable lens? (vii) Prior to getting laser eye surgery, a person wore corrective lenses to correct for long sightedness. Draw a ray diagram to show the formation of an image in the eye. Include the lens system of the eye and the corrective lens in your diagram. (viii) Give two reasons why lasers are used in eye surgery. (8 7) 2015.1 L.36 9/12 page 9 of 12
12. Answer any two of the following parts (a), (b), (c), (d). (a) Define centripetal force. (6) A car of mass 2000 kg takes off from rest from traffic light A and accelerates, at a constant rate in a straight line, to traffic light B, a distance of 100 m away. The car passes through traffic light B and continues at constant speed around a circular bend of radius 50 m (through a quarter of a circle as shown). It then continues, at constant speed, in a straight line to traffic light C, a distance of 70 m from the end of the bend. Traffic light C 50 m 70 m 100 m Traffic light B Traffic light A The minimum frictional force between the car and the road that is required to keep the car travelling around the bend is 16 kn. Calculate the maximum speed at which the car can travel around the bend. (6) The car travels from traffic light A to traffic light C, not exceeding this maximum speed, in the shortest time. (i) Find the average net force supplied to the car from traffic light A to traffic light B. (ii) Find the time taken to travel from traffic light A to traffic light C. (16) (b) State the units for (i) sound intensity and (ii) sound intensity level. (6) An alarm at a factory goes off at night. After 10 minutes the sound intensity observed by a stationary person multiplies by 4. What change is observed in the sound intensity level? (6) If there is no further change in the sound intensity at that point, how many times further than the original distance should the person move away from the alarm so that they observe the same sound intensity as when the alarm originally went off? (10) The observer is using a sound-level meter based on the db(a) scale. Why would they use this type of meter? (6) 2015.1 L.36 10/12 page 10 of 12
(c) Explain how point discharge occurs. (9) The diagram shows three small spheres containing charges of +2 μc, +6 μc and +8 μc held 20 cm apart in a straight line. 20 cm 20 cm 2 μc 6 μc 8 μc Calculate the electric field strength at the position of the 6 μc charge. (12) How far does the 2 μc charge have to be moved so that the electric field strength at the 6 μc charge becomes zero? (7) (d) State the law of radioactive decay. (6) In Ernest Rutherford s experiments that determined the presence of the nucleus in atoms, radium 226 was used as the source of alpha-particles. The sample he used produced approximately 4 billion decays per second. What was observed by Rutherford in these experiments? (7) Calculate the number of undecayed radium 226 nuclei in the sample. Hence, calculate the mass of the sample used. (15) 2015.1 L.36 11/12 page 11 of 12
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