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

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.

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.

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

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.

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.

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

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?

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? M1a1= M2a2 = F = kq2/r2 M2= M1a1/a2 = 2.86x10-7 kg q2 = r2 M1a1/k q = 4.68x10-11 C

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

Phy 2049: Physics II 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? FX = .607N Fy = -.303 N

Induction and Contact How much charge is transferred when they touch? 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?

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. 3/16

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

Coulombs law Properties of charges Electric fields Summary Coulombs law Properties of charges Electric fields