Phy 2049: Physics II

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Phy 2049 Physics II

• Syllabus, grades and exams
• Electricity, Magnetism, optics
• Charge
• Force
• Constants

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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.

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Phy 2049 Homework

• Visit wileyplus
• Physics is a little like riding bicycle. No one
  has learned how to ride a bicycle by reading an
  owners 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.

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Phy 2049 Homework

• Coulombs law
• Addition of forces as vectors
• Induction and contact
• Electric fields and field lines

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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.

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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.

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Phy 2049 Physics II

• Coulombs 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

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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?
  2.86e-07 kg
• What is the magnitude of the charge of each
  particle? 4.68e-11 C

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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

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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) x 0.607 N and b) y -0.303 N
  components of the net electrostatic force on
  particle 3?

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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?

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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

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Summary

• Coulombs law
• Properties of charges
• Electric fields