Phys 150 Lecture 71 Please sit together in pairs: –Onyema and John W. –Alejandra and Dian –Chris and Michael –Ryan and Honglu –John F. and Matt –Walter and Lin –Max and Anwen –Amanda and Mengyue –Pauline and Melissa –Jennifer and Erich –Alexandra and Irfan –David and Jason –Abigael and Jiayuan –Jake and Erica

Phys 150 Lecture 122 Announcements Homework 7 is due on Sunday, March 10 at midnight. Quiz on Chapter 7 on Tuesday, March 12

Phys 150 Lecture 133 Chapter 6 – Electricity and Magnetism Magnetism Bar magnets

Phys 150 Lecture 134 i>clicker question Magnetism is created by A.electric charges B.electric currents C.magnetic charges D.magnetic currents

Phys 150 Lecture 135 i>clicker question Magnetism is created by A.electric charges B.electric currents C.magnetic charges – don’t exist D.magnetic currents – also don’t exist -Permanent magnet: spinning electrons -Electromagnet: electric current Magnetic fields Electromagnet Superconductor

Phys 150 Lecture 136 i>clicker question A magnetic field exerts a force on A.moving electric charges B.electric currents C.other magnets D.All of the above

Phys 150 Lecture 137 i>clicker question A magnetic field exerts a force on A.moving electric charges B.electric currents C.other magnets D.All of the above -Electric current = moving electric charges Television Electric generator Rail Gun

Phys 150 Lecture 138 i>clicker question An electric motor A.is identical to an electric generator B.uses an electric field and a magnetic field C.uses only electric fields D.switches back and forth between electric and magnetic fields

Phys 150 Lecture 139 i>clicker question An electric motor A.is identical to an electric generator B.uses an electric field and a magnetic field C.uses only electric fields D.switches back and forth between electric and magnetic fields -Hybrid autos have “motor/generators” -They also have rectifiers (AC -> DC) and inverters (DC -> AC) Electric motor

Phys 150 Lecture 1310 i>clicker question A changing magnetic field produces A.another magnetic field B.an electric field C.AC current D.DC current

Phys 150 Lecture 1311 i>clicker question A changing magnetic field produces A.another magnetic field B.an electric field C.AC current D.DC current -This is called magnetic induction -The produced electric field can then generate a current Coil and magnet Transformer

Phys 150 Lecture 1312 i>clicker question A step-up transformer increases the voltage and A.increases the current B.decreases the current C.increases the power D.decreases the power

Phys 150 Lecture 1313 i>clicker question A step-up transformer increases the voltage and A.increases the current B.decreases the current C.increases the power D.decreases the power -P = IV cannot change (conservation of energy) -Increase V -> Decrease I

Phys 150 Lecture 1314 i>clicker question The Earth’s magnetic field is produced by A.permanent magnets in the Earth’s outer core B.permanent magnets in the Earth’s inner core C.electric currents in the Earth’s outer core D.electric currents in the Earth’s inner core

Phys 150 Lecture 1315 i>clicker question The Earth’s magnetic field is produced by A.permanent magnets in the Earth’s outer core B.permanent magnets in the Earth’s inner core C.electric currents in the Earth’s outer core D.electric currents in the Earth’s inner core -The outer core is liquid (molten iron and nickel) -The inner core is solid (iron and nickel)

Phys 150 Lecture 1316 i>clicker question The Earth’s magnetic field flips A.about once every 100 years B.about once every 10,000 years C.about once every million years D.about once every 100 million years

Phys 150 Lecture 1317 i>clicker question The Earth’s magnetic field flips A.about once every 100 years B.about once every 10,000 years C.about once every million years D.about once every 100 million years -Why? How?