Major Concepts of Physics PHY102 – Lecture #  Syracuse University Lecture #3 Magnetic fields and forces January 27 th, 2016 Prof. Liviu Movileanu Room 211, Physics Bldg., Major Concepts of Physics PHY102

Major Concepts of Physics PHY102 – Lecture #  Syracuse University What’s the link for the ebook? Here is the correct link for Physics 3/e

Major Concepts of Physics PHY102 – Lecture #  Syracuse University 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 #  Syracuse University

Major Concepts of Physics PHY102 – Lecture #  Syracuse University Why do we have a tilt of the magnetic field? Cross-product

Major Concepts of Physics PHY102 – Lecture #  Syracuse University Conceptual example Continuation

Example (text problem 19.20): An electron moves with speed 2.0  10 5 m/s in a 1.2 Tesla uniform magnetic field. At one instant, the electron is moving due west and experiences an upward magnetic force of 3.2  10  14 N. What is the direction of the magnetic field? v (west) F (up) y x   The angle can be either north of west OR north of east. Major Concepts of Physics PHY102 – Lecture #  Syracuse University north east

§ 19.3 Charged Particle Moving Perpendicular to a Uniform B-field 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 #  Syracuse University v FBFB

Applying Newton’s 2 nd Law to the charge: Major Concepts of Physics PHY102 – Lecture #  Syracuse University Conceptual example

Mass Spectrometer A charged particle is shot into a region of known magnetic field. Here, Particles of different mass will travel different distances before striking the detector. (v, B, and q can be controlled.) V Detector B Major Concepts of Physics PHY102 – Lecture #  Syracuse University

Other devices that use magnetic fields to bend particle paths are cyclotrons and synchrotrons. Cyclotrons are used in the production of radioactive nuclei. For medical uses see the website of the Nuclear Energy Institute.Nuclear Energy Institute Synchrotrons are being tested for use in treating tumors. Major Concepts of Physics PHY102 – Lecture #  Syracuse University Conceptual example Continuation

Fig Major Concepts of Physics PHY102 – Lecture #  Syracuse University Ernest Lawrence Cyclotron

Major Concepts of Physics PHY102 – Lecture #  Syracuse University Proton-beam radiosurgery

§ 19.6 Magnetic Force on a Current Carrying Wire The force on a current carrying wire in an external magnetic field is L is a vector that points in the direction of the current flow. Its magnitude is the length of the wire. Major Concepts of Physics PHY102 – Lecture #  Syracuse University

The magnitude of is and its direction is given by the right-hand rule. Major Concepts of Physics PHY102 – Lecture #  Syracuse University Conceptual example Continuation

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 B Left: F out of page Top: no force Right: F into page Bottom: no force Major Concepts of Physics PHY102 – Lecture #  Syracuse University Conceptual example L1L1 L2L2

The magnitudes of the nonzero forces are: (b) What is the net force on the loop? Example continued: Major Concepts of Physics PHY102 – Lecture #  Syracuse University Conceptual example Continuation

Fig Major Concepts of Physics PHY102 – Lecture #  Syracuse University

Major Concepts of Physics PHY102 – Lecture #  Syracuse University 1.This week we will have the first workshop (Workshop #1), titled “Electric Motor” 1.Read textbook materials, pp Sections 19.3 Charged particle moving perpendicularly to a uniform magnetic field pp , Magnetic force on a current-carrying wire pp Conceptual examples 19.2, 19.3, Homework assignment HW #1 is due on next week’s lab sessions. This is Problems 1-8 on pages of the text.Announcements