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Major Concepts of Physics PHY102 Lecture #3 Magnetic fields and forces January 25th, 2017 Prof. Liviu Movileanu http://movileanulab.syr.edu/MajorConceptsPhysics.html [email protected] Room 211, Physics Bldg., 443-8078 Major Concepts of Physics PHY102 – Lecture #3 1 Lecture objectives • Motion of a Charged Particle in a Magnetic Field – Continuation • Magnetic force on a current-carrying wire • Lecture demonstrations • Conceptual Examples • Announcements/Homework Assignment Major Concepts of Physics PHY102 – Lecture #3 2 3 Conceptual example 19.2 - Continuation Major Concepts of Physics PHY102 – Lecture #3 4 Why do we have a tilt of the magnetic field? Major Concepts of Physics PHY102 – Lecture #3 5 §19.3 Charged Particle Moving Perpendicular to a Uniform B-field Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä FB Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä v A positively charged particle has a velocity v (orange arrow) as shown. The magnetic field is into the page. The magnetic force, at this instant, is shown in blue. In this region of space, this positive charge will move in a circular path. Major Concepts of Physics PHY102 – Lecture #3 6 §19.3 Charged Particle Moving Perpendicular to a Uniform B-field Applying Newton’s 2nd Law to the charge: åF = F B = mar v2 qvB = m r Major Concepts of Physics PHY102 – Lecture #3 7 Mass Spectrometer A charged particle is shot into a region of known magnetic field. B Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Ä Detector V 2 Here, v qvB = m r or qBr = mv = p Particles of different mass will travel different distances before striking the detector. (v, B, and q can be controlled.) Major Concepts of Physics PHY102 – Lecture #3 8 Other devices that use magnetic fields to bend particle paths are cyclotrons and synchrotrons. Synchrotrons are being tested for use in treating tumors. Ernest Lawrence 1929 - Cyclotron Major Concepts of Physics PHY102 – Lecture #3 9 Proton-beam radiosurgery Major Concepts of Physics PHY102 – Lecture #3 10 Magnetic force on a current carrying wire The magnitude of force is F = I (L ´ B) is and its direction is given by the right-hand rule. Where F is magnetic force, L is a length vector, and B is a magnetic field vector. Major Concepts of Physics PHY102 – Lecture #3 11 Conceptual example 19.50 Example (text problem 19.50): A 20.0 cm by 30.0 cm loop of wire carries 1.0 A of current clockwise. (a) Find the magnetic force on each side of the loop if the magnetic field is 2.5 T to the left. I = 1.0 A Left: F out of page L1 Top: no force B Right: F into page Bottom: no force L2 Major Concepts of Physics PHY102 – Lecture #3 12 Conceptual example 19.2 - Continuation Example continued: The magnitudes of the nonzero forces are: F = ILB sin q = (1.0 A )(0.20 m )(2.5 T )sin 90° = 0.50 N (b) What is the net force on the loop? Fnet = 0 Major Concepts of Physics PHY102 – Lecture #3 13 Announcements 1. This week we will have the first workshop (Workshop #1) 2. Read textbook materials, pp. 707-717. 3. Sections 19.3 Charged particle moving perpendicularly to a uniform magnetic field pp. 717-718, 720-721 19.6 Magnetic force on a current-carrying wire pp. 727-728 Conceptual examples 19.2 3. Homework assignment HW #1 is due on next week’s lab sessions. This is Problems 1-8 on pages 745-746 of the text (Please do not look at multiple-choice questions, which are on the same). Major Concepts of Physics PHY102 – Lecture #2 14