PowerPoint PresentationHow Do You Use Magnetic Fields in Your Everyday Life!?Lecture 18: FRI 26 FEBSlide 4Electric vs. Magnetic FieldsSlide 6Slide 7Magnetic vs. Electric ForcesSlide 9Definition of Magnetic FieldSlide 11Slide 12Slide 13QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.How Do You Use Magnetic Fields in Your Everyday Life!?Lecture 18: FRI 26 FEB Lecture 18: FRI 26 FEB Magnetic fields Magnetic fields Ch.28.1–5 Physics 2102Jonathan Dowling“I’ll be back….Aurora BorealisQuickTime™ and a decompressorare needed to see this picture.Second Exam Review:6-7PM WED 04 MAR Nicholson 130Second Exam (Chapters 24–28):6–7PM THU 05 MAR Lockett 6Electric vs. Magnetic FieldsElectric vs. Magnetic FieldsElectric fields are created:• microscopically, by electric charges (fields) of elementary particles (electrons, protons)• macroscopically,by adding the field of many elementary charges of the same signMagnetic fields are created :• microscopically, by magnetic “moments” of elementary particles (electrons, protons, neutrons)• macroscopically, by • adding many microscopic magnetic moments (magnetic materials); or by• electric charges that move (electric currents)Magnetic Field DirectionFROM North PolesTO South PolesB+–Compare to ElectricField DirectionsEQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Ritchie’s Rule for MagnetsOpposite Poles AttractLike Poles RepelWe know that an electric fields exists because it accelerates electric charges, with a force independent of the velocity of the charge, proportional to the electric charge: FE = qEWe know that a magnetic field exists because it accelerates electric charges in a direction perpendicular to the velocity of the charge, with a magnitude proportional to the velocity of the charge and to the magnitude of the charge: FB= q v x BMagnetic forces are perpendicular to both the velocity of chargesand to the magnetic field (electric forces are parallel to the field).Since magnetic forces are perpendicular to the velocity,they do no work! (W=F · r)Speed of particles moving in a magnetic field remains constantin magnitude, ONLY the direction changes. Kinetic energy is constant! (no work).Magnetic vs. Magnetic vs. Electric ForcesElectric ForcesMagnetic vs. Electric ForcesMagnetic vs. Electric Forces € r F E= qr E € r F E= qr E Electric Force on Charge Parallel to E:Electric Force on Charge Parallel to E: € r F B= qr v ×r B € r F B= qr v ×r B Magnetic Force on Charge Perpendicular to B and v. Magnetic Force on Charge Perpendicular to B and v. +q € r F E € r F E € r E € r E € r F B € r F B € r B € r B +q € r v € r vDefinition of Magnetic Definition of Magnetic FieldField € r E =r F Eq € r E =r F EqDefinition of Electric Field:Definition of Electric Field: € B =r F Bqr v € B =r F Bqr v Definition of Magnetic Field:Definition of Magnetic Field:€ Units : B =NewtonCoulomb ⋅ meter/sec( ) ⎡ ⎣ ⎢ ⎤ ⎦ ⎥=NewtonCoulomb/sec( )⋅meter ⎡ ⎣ ⎢ ⎤ ⎦ ⎥=NewtonAmpere ⋅meter ⎡ ⎣ ⎢ ⎤ ⎦ ⎥=NA ⋅m ⎡ ⎣ ⎢ ⎤ ⎦ ⎥€ Units : B =NewtonCoulomb ⋅ meter/sec( ) ⎡ ⎣ ⎢ ⎤ ⎦ ⎥=NewtonCoulomb/sec( )⋅meter ⎡ ⎣ ⎢ ⎤ ⎦ ⎥=NewtonAmpere ⋅meter ⎡ ⎣ ⎢ ⎤ ⎦ ⎥=NA ⋅m ⎡ ⎣ ⎢ ⎤ ⎦ ⎥QuickTime™ and a decompressorare needed to see this picture.Thompson ExperimentForces Balance: v=E/BL€ E ≠ 0, B = 0; qE = FE= maa = FE/m = qE /mL = vt; y =12at2; Solve : y =qEL22mv2yII: E≠0, B=0I: E=0, B=0III: vB=E€ v = E /B; y =qEL22mv2y =qEL2B22mE2=qL2B22mE€ mq=L2B22yEQuickTime™ and a decompressorare needed to see this
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