Lect08 handout

Magnetism Physics 102: Lecture 08 This material is NOT on exam 1!

Lecture Overview ,[object Object],[object Object],[object Object],[object Object]

Magnets & magnetic fields ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

No Magnetic Charges ,[object Object],[object Object],[object Object],We’ll return to this in Lecture 25 & 26 Orbits of electrons about nuclei Intrinsic “spin” of electrons (more important effect)

Magnetic Fields and Forces ,[object Object],Magnitude Direction ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Note: there are different versions of RHR

ACT: Direction of Magnetic Force on + Moving Charge ,[object Object],[object Object],[object Object],1) Up 2) Down 3) Right 4) Left 5) Zero out of page up

Direction of Magnetic Force on Moving Charges ,[object Object],[object Object],[object Object],[object Object],[object Object],right left

Preflight 8.3 What is the direction of the force on the particle just as it enters region 1? 1) up 2) down 3) left 4) right 5) into page 6) out of page 1 2 v = 75 m/s q = +25 mC Each chamber has a unique magnetic field. A positively charged particle enters chamber 1 with velocity 75 m/s up, and follows the dashed trajectory.

Preflight 8.4 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],1 2 v = 75 m/s q = +25 mC Each chamber has a unique magnetic field. A positively charged particle enters chamber 1 with velocity 75 m/s up, and follows the dashed trajectory. B 1

ACT: 2 Chambers ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],1 2 v = 75 m/s q = +25 mC Each chamber has a unique magnetic field. A positively charged particle enters chamber 1 with velocity 75 m/s up, and follows the dashed trajectory. B 2

Magnitude of Magnetic Force on Moving Charges Only component of v ⊥ to B (or B ⊥ to v) matters If v is parallel to B then F = 0 Does not matter whether you use  or 180 –  B  V Force depends on magnitude of charge, velocity, and magnetic field B ⊥ V ⊥ 

ACT: Moving Charges ,[object Object],[object Object],[object Object],[object Object],[object Object],B 1 2 3 F = qvBsin(  )

Comparison Electric vs. Magnetic ,[object Object],[object Object],[object Object],[object Object],[object Object]

Velocity Selector ,[object Object],v E For straight line, need |F E |= |F B | q E= q v B sin(90) B = E/v What direction should B point if you want to select negative charges? A) Into Page B) Out of page C) Left D) Right F E would be up so F B must be down. Electric force is down, so need magnetic force up. By RHR, B must be into page Example F E F B

Motion of q in uniform B field ,[object Object],[object Object],[object Object],[object Object],Uniform B into page ,[object Object],[object Object],Recall circular motion from Phys 101 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x v F v F v F v F v F v F R

Preflight 8.6 ,[object Object],[object Object],[object Object],[object Object],1 2 v = 75 m/s q = +25 mC Each chamber has a unique magnetic field. A positively charged particle enters chamber 1 with velocity v 1 = 75 m/s up, and follows the dashed trajectory.

Preflight 8.8 ,[object Object],[object Object],[object Object],[object Object],1 2 v = 75 m/s q = +25 mC Each chamber has a unique magnetic field. A positively charged particle enters chamber 1 with velocity v 1 = 75 m/s up, and follows the dashed trajectory.

ACT: 2 chambers ,[object Object],[object Object],[object Object],[object Object],1 2 v = 75 m/s q = ?? mC Each chamber has a unique magnetic field. A positively charged particle enters chamber 1 with velocity v 1 = 75 m/s up, and follows the dashed trajectory.

Summary ,[object Object],[object Object]

Lect08 handout

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