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Faraday Cages

Faraday Cages. Van der Graaf generator at Boston Museum of Science. Music group ArcAttack. Charge  3 nC is in a hollow cavity inside a large chunk of metal that is electrically neutral. The total charge on the exterior surface of the metal is 0 nC. +3 nC. –3 nC.

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Faraday Cages

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  1. Faraday Cages Van der Graaf generator at Boston Museum of Science Music group ArcAttack

  2. Charge 3 nC is in a hollow cavity inside a large chunk of metal that is electrically neutral. The total charge on the exterior surface of the metal is • 0 nC. • +3 nC. • –3 nC. • Can’t say without knowing the shape and location of the hollow cavity.

  3. Discussion question: conductor with holes Charges qb and qc are positive and negative with qb having the larger magnitude, qd is positive, r is large compared to size of metal sphere. What are the forces on the three charges and on the sphere?

  4. The electric flux through the shaded surface is • 0. • 400cos20 N m2/C. • 400cos70 N m2/C. • 400 N m2/C. • Some other value.

  5. Which surface, A or B, has the larger electric flux? Surface A has more flux. Surface B has more flux. The fluxes are equal. It’s impossible to say without knowing more about the electric field.

  6. Quick Proof of Gauss's Law

  7. Surfaces A and B have the same shape and the same area. Which has the larger electric flux? • Surface A has more flux. • Surface B has more flux. • The fluxes are equal. • It’s impossible to say without knowing more about the electric field.

  8. Which spherical Gaussian surface has the larger electric flux? • Surface A. • Surface B. • They have the same flux. • Not enough information to tell.

  9. Spherical Gaussian surfaces of equal radius R surround two spheres of equal charge Q. Which Gaussian surface has the larger electric field? • Surface A. • Surface B. • They have the same electric field. • Not enough information to tell.

  10. A spherical Gaussian surface surrounds an electric dipole. The net enclosed charge is zero. Which is true? The electric field is zero everywhere on the Gaussian surface. The electric field is not zero everywhere on the Gaussian surface. Whether or not the field is zero on the surface depends on where the dipole is inside the sphere.

  11. The electric flux is shown through two Gaussian surfaces. In terms of q, what are charges q1 and q2? • q1 = 2q; q2 = q. • q1 = q; q2 = 2q. • q1 = 2q; q2 = –q. • q1 = 2q; q2 = –2q. • q1 = q/2; q2 = q/2.

  12. A cylindrical Gaussian surface surrounds an infinite line of charge. The fluxethrough the two flat ends of the cylinder is • 0. • 2  2rE. • 2 r2E. • 2 rLE. • It will require an integration to find out.

  13. QuickCheck 27.13 A cylindrical Gaussian surface surrounds an infinite line of charge. The fluxethrough the wall of the cylinder is • 0. • 2rLE • r2LE. • rLE. • It will require an integration to find out. Slide 27-95

  14. A point charge q is located distance rfrom the center of a neutral metal sphere. The electric field at the center of the sphere is • . • . • . • 0. • It depends on what the metal is.

  15. Assigning Normal Area Vectors to Small Patches of Closed Surface

  16. Flux Corresponds to Amount of “Fluid”Passing Through Area Per Unit Time

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