North Berwick High School Department of Physics Higher Physics Unit 2 Particles and Waves Section 2 Forces on Charged Particles Section 2 Forces on Charged Particles Note Making Make a dictionary with the meanings of any new words. Electric charge 1. Explain, in terms of simple electrostatics, why the electrons flow from negative to positive. Magnetic fields 1. Explain the concept of a magnetic field. Motion of Charged Particles in a Magnetic Field 1. Describe the motion of a charged particle travelling parallel or antiparallel to a magnetic field. 2. Describe the motion of a charged particle travelling perpendicular to a magnetic field. 3. Draw the pattern produced by a charged particle in a bubble chamber. Explain how these patterns are produced. Electric fields 1. Draw the patterns produced by two point sources, a positive point charge, a negative point charge and parallel plates. 2. Explain the direction of the field lines and the information they give us. 3. Describe the motion of a charged particle in an electric field. 4. Copy the example on page 15. 5. Copy the example starting on page 17 which relates to the electric field produced in a CRT. 6. Work through the ‘check your understanding section’. Particle accelerators 1. Describe the 5 main reasons for building the LHC 2. Describe the main components of a particle accelerator. 3. List the three types of particle accelerators. 4. Briefly describe the main experiments at the LHC. Section 2 Forces on Charged Particles Contents Content Statements ........................................................................................ 1 Particles and waves......................................................................................... 2 Electric charge ................................................................................................. 3 Magnetic fields................................................................................................ 4 Motion of Charged Particles in a Magnetic Field ........................................... 4 Deflections of charged particles in a bubble chamber ................................... 7 Electric fields ................................................................................................... 8 Using gravitational fields to help understand electric fields ........................ 11 Describe what happens to the energy of an object raised in a gravitational field ................................................................................... 11 Moving charged particles in electric fields: useful applications ................... 16 Particle accelerators ..................................................................................... 20 Why the LHC?................................................................................................ 21 A few unanswered questions... .................................................................... 21 Newton’s unfinished business... ................................................................... 21 An invisible problem... .................................................................................. 22 Nature’s favouritism... .................................................................................. 22 Secrets of the Big Bang ................................................................................. 23 Hidden worlds… ............................................................................................ 23 Facts and figures ........................................................................................... 24 The largest machine in the world... .............................................................. 24 The fastest racetrack on the planet... ........................................................... 24 The emptiest space in the Solar System... .................................................... 24 The hottest spots in the galaxy, but even colder than outer space... .......... 25 The biggest and most sophisticated detectors ever built... ......................... 25 The most powerful supercomputer system in the world... .......................... 25 How an accelerator works ............................................................................ 26 The physics of particle accelerators ............................................................. 27 The LHC: a look inside ................................................................................... 28 The accelerator ............................................................................................. 28 The experiments ........................................................................................... 35 ATLAS and CMS ............................................................................................. 37 LHCb .............................................................................................................. 38 ALICE ............................................................................................................. 39 The data challenge ........................................................................................ 40 Who works on the LHC? ............................................................................... 40 Problems ....................................................................................................... 44 Solutions ....................................................................................................... 54 Content Statements Content notes context a) Electric fields Examples of electric field Hazards, e.g. lightning, around charged patterns include single static electricity on particles and point charges, systems of microchips. between parallel two point charges and the plates. field between parallel plates. No calculation of electric field strength required. b) Movement of The relationship between Precipitators. Xerography. charge in an potential difference, work Paint spraying. electric field, p.d. and charge gives the Ink jet printing. and work, electrical definition of the volt. Electrostatic propulsion. energy. Calculating the speed of a charged particle accelerated in an electric field. c) Charged particles in A moving charge produces a magnetic field. a magnetic field. The direction of the force on a charged particle moving in a magnetic field should be described for negative and positive charges (right hand rule for negative charges). No calculations required. d) Particle Basic operation of Accelerators include linear accelerators. accelerator, cyclotron and particle accelerators in terms of acceleration, synchroton. deflection and collision Medical applications of cyclotron. of charged particles. Accelerators used to probe structure of matter. 1 Section 2 Particles and waves In this section we will explore the idea of the force field in physics, in relation to electric charge. Having studied electricity at a lower level, you may feel confident that you have a good grasp of the concepts surrounding electricity. Rest assured there will be new challenges in this section of work. Like many areas of physics, we build our understanding in a spiral – revisiting previous topics and building on them to extend our conceptual understanding, and explaining this verbally, graphically, mathematically, visually and in writing. Lord Kelvin (1824–1907) recognised the challenges associated with scientific understanding: But when I think how infinitely little is all that I have done I cannot feel pride; I only see the great kindness of my scientific comrades, and of all my friends in crediting me for so much. One word characterises the most strenuous of the efforts for the advancement of science that I have made perseveringly during fifty-five years; that word is failure. I know no more of electric and magnetic force, or of the relation between ether, electricity, and ponderable matter, or of chemical affinity, than I knew and tried to teach to my students of natural philosophy fifty years ago in my first session as Professor. Something of sadness must come of failure; but in the pursuit of science, inborn necessity to make the effort brings with it much of the certaminis gaudia, and saves the naturalist from being wholly miserable, perhaps even allows him to be fairly happy in his daily work. And what splendid compensation for philosophical failures we have had in the admirable discoveries by observation and experiment on the properties of matter, and in the exquisitely beneficent applications of science to the use of mankind with which these fifty years have so abounded! Lord Kelvin (William Thomson), Professor of Natural Philosophy, University of Glasgow (1846–1899) on the occasion of Lord Kelvin’s 50-year jubilee as a professor. 2 Michael Faraday (1791–1867) noted: The cases of action at a distance are becoming, in a physical point of view, daily more and more important. Sound, light, electricity, magnetism, gravitation, present them as a series. The nature of sound and its dependence on a medium we think we understand, pretty well. The nature of light as dependent on a medium is now very largely accepted. The presence of a medium in the phenomena of electricity and magnetism becomes more and more probable daily. We employ ourselves, and I think rightly, in endeavouring to elucidate the physical exercise of these forces, or their sets of antecedents and consequents, and surely no one can find fault with the labours which eminent men have entered upon in respect of light, or into which they may enter as regards electricity and magnetism. Then what