1 / 11

CHAPTER-28

CHAPTER-28. Magnetic Field. Ch 28-2 What produces a Magnetic Field?. Electric field E produces a electric force F E on a stationary charge q Magnetic field B produces a magnetic force F B on a moving charge q

reya
Download Presentation

CHAPTER-28

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHAPTER-28 Magnetic Field

  2. Ch 28-2 What produces a Magnetic Field? • Electric field E produces a electric force FE on a stationary charge q • Magnetic field B produces a magnetic force FB on a moving charge q • What produces a Magnetic Field? A Magnetic Monopole? Magnetic monopoles do not exists • Two ways to produce magnetic field B: Electromagnet: magnetic field due to a current Permanent magnet: net magnetic field due to intrinsic magnetic field of electrons in certain material.

  3. Ch 28-3 The Definition of B • Electric field E: E field is tested by measuring force FE on a static charge q E=FE/q • Magnetic Field B is tested by measuring force FB on a moving charge q. If v is charge velocity then FB=q(vxB)=qvBsin • is angle between the v and B. • Direction of B: that direction of V for which FB=0 • Direction of FB:  to plane of V and B

  4. Ch 28-3 The Definition of B • Unit of B Tesla (T): B=FB/qvsin SI unit of magnetic field B (T):Newtons/Coulomb.(m/s) = N/(C/s).m=N/A.m 1T=1N/A.m • Magnetic Field Lines: • B field line starts from N pole ans terminates at S pole • Like magnetic pole repel each other and opposite pole attract each other.

  5. Ch 28-4 Crossed Fields • Crossed fields: a region with E and B field  to each other. If the net force due to these two fields on a charge particle is zero, particle travels undeviated Then FE=FB qE=qvB (=90) E=vB or v=E/B

  6. Ch 28-6 A Circulating Charged Particle • When a charge q moves in a B field then the magnetic force FB=qvBsin=qvB (=90) • For =90 the particle moves in a circular orbit wit a radius given by : FR=FB • mv2/R=|q|vB (m is particle mass) • R=mv/qB or v=|q|RB/m • Particle period T=2R/v • Frequency f=1/T=v/2R • Angular frequency =2f =2f=v/R=|q|B/m If v has a component along B then particle trajectory is a helix (helical path)

  7. Ch 28-8 Magnetic Force on a Current-Carrying Wire • A force is exerted by a magnetic field B on a charge +q moving with velocity v. • Direction of force is same for an electron (-q) moving with velocity vD( in opposite direction to v). • For a wire carrying a current i, number of electrons passing a length of wire L in time t are q-given by : • q-=it=iL/vD & q- =-q and vD=-v • q-=iL/vD reduces to q=iL/v Then FB=q(vxB)= (iL/v)(vxB) FB = i(LxB) FB = iLB

  8. Ch 28-9 Torque on a Current Loop A current carrying rectangular loop placed between the N and S poles of a magnet, no magnetic force on shorter sides but forces in opposite direction on longer sides

  9. Ch 28-9 Torque on a Current Loop Same Magnitude of forces F2 and F4 on shorter sides F2=F4=ibBcos Same Magnitude of forces F1 and F3 on longer sides F1=F3=iaBsin=iaB Net torque due to F1 and F3 is ’ = iaB x (bsin/2) + iaB x (bsin/2) =iabBsin ’ =iABsin= i(AxB)=i

  10. Ch 28-10 Magnetic Dipole Moment • Magnetic moment of a coil: • =NiA ( A is coil area); Then  =  x B =NiAB sin • Torque  exerted on an electric dipole p in an electric field E :  = p x E • Torque due to electric or magnetic field = vector product of dipole moment and field vector • Electric potential energy U() of a electric dipole moment p in an E field U()= -p.E • Magnetic potential energy of a magnetic dipole  U() = -  . B = -  B cos Max. value of U() : for  = 180 Min. value of U() for  =0 Work done by a magnetic field in rotating a a magnetic dipole from initial orientation i to final orientation f W=-U= -(Uf-Ui) Wappl=-W

  11. Suggested problems Chapter 28

More Related