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Phy 2049: Physics II

Phy 2049: Physics II. Syllabus, grades and exams Electricity, Magnetism, optics Charge Force Constants. Phy 2049: Homework.

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Phy 2049: Physics II

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  1. Phy 2049: Physics II Syllabus, grades and exams Electricity, Magnetism, optics Charge Force Constants 2049, summerC, ‘07

  2. Phy 2049: Homework • Because the summer semester is quite short, the homework assignments are rather large. I would suggest that you do as many as you can at the earliest chance possible. I would certainly urge you not to try them all the night before they are due.

  3. Phy 2049: Homework • Visit wileyplus • Physics is a little like riding bicycle. No one has learned how to ride a bicycle by reading an owner’s manual. • It is very hard in the beginning, but then it becomes instinctive. That is when you start to enjoy the scenery • Try doing homework in a group.

  4. Phy 2049: Homework • Coulomb’s law • Addition of forces as vectors • Induction and contact • Electric fields and field lines

  5. Charges and Polarization • Two kinds of charges, positive and negative, unit is 1.6x10-19 Coulombs. • Like Charges repel. It takes force to hold them in place. • Induction: • Polarization is attractive. Like charges move back and unlike charges move up. • Contact leads to repulsion. Only like charges are left to be redistributed.

  6. Natural particles • Electrons are very light (m = 9.11 x10-31 kg). Their charge is 1.6x10-19 Coulomb. • Protons and neutrons are same weight (nearly so, m = 1.67x10-27 kg = 1/N ). Protons are positively charge but the neutrons are neutral.

  7. Phy 2049: Physics II • Coulomb’s Law • F in Newtons, r in meter, q in Coulomb and k is the fix. • F is a vector, directed along a line joining the charges. • The force can be added like a vector

  8. Phy 2049: Physics II • Two equally charged particles are held 2.5X 10-3 m apart and then released from rest. The initial acceleration of the first particle is observed to be 5.0 m/s2 and that of the second to be 11.0 m/s2. The mass of the first particle is 6.3X10-7 kg. What is the mass of the second particle? What is the magnitude of the charge of each particle?

  9. Two equally charged particles are held 2.5X 10-3 m apart and then released from rest. The initial acceleration of the first particle is observed to be 5.0 m/s2 and that of the second to be 11.0 m/s2. The mass of the first particle is 6.3X10-7 kg. What is the mass of the second particle? What is the magnitude of the charge of each particle? M1a1= M2a2 = F = kq2/r2 M2= M1a1/a2 = 2.86x10-7 kg q2 = r2 M1a1/k q = 4.68x10-11 C Phy 2049: Physics II

  10. Directions of Forces • Between two charged particles forces are directed along a line joining them. • Can be added as vectors

  11. In Fig. at right, the particles have charges q1 = -q2 = 298 nC and q3 = -q4 = 280 nC, and distance a = 4.0 cm. What are the a) Fx and b) Fy components of the net electrostatic force on particle 3? Phy 2049: Physics II

  12. Induction and Contact • What is the force between the balls in each case? • How much charge is transferred when they touch? • Calculate the force between the balls after they have touched?

  13. Touching charges • Three identical balls, 2q, q and –q • A touches B and separated back. • B touches C and separated back • Ratio of Force FAB now to force FAB at the start.

  14. Force and Electric Fields F = qE Electric field is the force felt by a unit positive charge Electric field lines come out of a positive charge and go into a negative charge. They do not cross

  15. Summary Coulombs law Properties of charges Electric fields

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