Question

Two similar spheres having in +Q and -Q charges kept at a certain distance.F force acts between the two.If middle of the two spheres , another similar spheres having +Q charge is kept,then its experience the force between magnitude and direction as

Answer 1

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Explanation:

Electrodynamics II Exam 2 problems Spring 2014

Section 21. Landau Problems 1-3

1. Consider two coaxial conducting cylinders with radii a and 3a and length L. The

region a<r<2a is filled with a material with conductivity σ1, and the region

2a<r<3a has conductivity σ2. Assume ε1 = ε2 = 1. The inner cylinder is held at

potential φ0 by a battery while the outer cylinder is grounded, so there is radial

current I. Determine the resistance in terms of σ1, σ2, and L. Determine the

surface charge density on the boundary at r = 2a.

2. A capacitor, filled with material of permittivity ε and conductivity σ, is charged to

Q0. (a) Find how the charge leaks off the plates with time. (b) Determine how

much of the initial stored energy is converted to heat. (c) What is the

characteristic time for discharge if the material is SiO2 (ε = 4.3, ρ = 1013 Ω-m)?

(d)What is the implication for computer memory chips?

3. The leakage resistance of cable insulation is measured by immersing a length of

insulated cable in salt water, applying a voltage between central conductor and

solution, and measuring the current. If length = 3 m, voltage = 200 V, the

insulation thickness is twice the central conductor radius, and a current of 2 nA is

measured, what is the resistivity of the insulation?

4. A steady current with uniform density j flows through a flat interface between a

medium with conductivity σ1 and permittivity ε1 and a medium with σ2 and ε2.

Find the extraneous charge that accumulates on the interface.