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Chapter 21, Electric Charge, and electric Field

Chapter 21, Electric Charge, and electric Field. HW 3: Chapter 21, Pb.1, Pb. 12, Pb.13, Pb.25, Pb. 31, Pb. 36 due Wednesday, Feb. 13 No quiz this coming Friday. Problem 20.

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Chapter 21, Electric Charge, and electric Field

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  1. Chapter 21, Electric Charge, and electric Field HW 3: Chapter 21, Pb.1, Pb. 12, Pb.13, Pb.25, Pb. 31, Pb. 36 due Wednesday, Feb. 13 No quiz this coming Friday

  2. Problem 20 20. (III) Two small positively charged spheres hang from cords of equal length l as shown in Fig. 21–55 and make small angles θ1 and θ2 with the vertical. (a) If Q1=Q, Q2=2Q, and m1=m2=m determine the ratio θ1/ θ2 (b) If Q1=Q, Q2=2Q, and m1=m and m2=2m, determine the ratio θ1/ θ2 (c) Estimate the distance between the spheres for each case.

  3. 21-6 Electric Field https://www.youtube.com/watch?v=xg0Lg-uSMSQ

  4. 21-6 The Electric Field Gravitational Field • Electric Field Units N/C + + -e + +

  5. 21-6 Electric Field: point charge If we have a charge (or a system of charges) we can ask ourselves what the electric field is at any point in space, P, a distance r from the charge. P -e Units: N/C r P +e r

  6. 21-6 The Electric Field The electric field is defined as the force on a small charge, divided by the magnitude of the charge: The electric field is a vector

  7. 21-6 The Electric Field For a point charge: ε0 is the permittivity of the free space=8.85x10-12C2/N.m2

  8. 21-6 The Electric Field Force on a point charge in an electric field, the direction of the force depends on the charge sign

  9. Electric Field: system of charges If we have a system of charges we can ask ourselves what the electric field is at any point in space, P? In this case we find the Electric field due to each charge in the system at that point, P, and we do a vector sum of these fields. r2 P Q2 r3 r1 Q3 Q1

  10. Problem 26

  11. Problem 27

  12. 21-6 The Electric Field Example 21-7: E at a point between two charges. Two point charges are separated by a distance of 10.0 cm. One has a charge of -25 μC and the other +50 μC. (a) Determine the direction and magnitude of the electric field at a point P between the two charges that is 2.0 cm from the negative charge. (b) If an electron (mass = 9.11 x 10-31 kg) is placed at rest at P and then released, what will be its initial acceleration (direction and magnitude)?

  13. 21.6 Electric Field 2-D Problem: Two charges are positioned as seen below. Q1= +2.0 µC and Q2= +8.0µC. What is the magnitude and the direction of the Electric Field at point P? y q1 r1=0.090m P q2 x r2=0.12m k = 8.99x10+9 Nm2/C2 = Coulomb’s constant

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