Problem 30.51 Part A A hollow metal sphere has inner radius a, outer radius b, a

Question

Problem 30.51 Part A A hollow metal sphere has inner radius a, outer radius b, and conductivity . The current I is radially outward from the inner surface to the outer surface Find an expression for the electric field strength inside the metal as a function of the radius r from the center Express your answer in terms of the variables 1,0, r, and appropriate constants Submit My Answers Give Up Correct Part B Evaluate the electric field strength at the inner surface of a copper sphere if a 1.1 cm . b = 2.8 cm , and 1-23 A Express your answer to two significant figures and include the appropriate units. E=( Value Units Submit Mv Answers Give Up Incorrect; Try Again; 4 attempts remaining Part C Evaluate the electric field strength at the outer surface of a copper sphere if a 1.1 cm , b = 2.8 cm , and 1-23 A Express your answer to two significant figures and include the appropriate units. alue Submit My Answers Give Up

Explanation / Answer

A)

If you were to consider a thin radial section of the cylinder (so that the cross section would be almost uniform throughout), what would be its resistance?
The radial area, not cross-sectional this time, is A = 2rL
the L = 2r A = 4r2
J = I/A = E E = I/(A) = I/(4r2)

B)

Givens/ Conversions:

a = 1.1 cm = 1.1×10-2 m

b = 2.8 cm = 2.8×10-2 m
I = 23 A
material = copper,

= 6.0×107 1/(m)

they want the strength at the inner surface, so use a as r...
E = (23 A)/[4(6.0×107 1/(m))(1.1×10-2 m)2]

E = 2.52×10-4 V/m

C)

they want the strength at the outer surface, so use a as r...
E = (23 A)/[4(6.0×107 1/(m))(2.8×10-2 m)2]

E = 3.9×10-5 V/m

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