(a) What is the radius of section 1? 1 mm (b) What is the radius of section 2? 2

Question

(a) What is the radius of section 1?
1           mm

(b) What is the radius of section 2?
2           mm I need help with b, i have got the answer for a bur can't seam to get the answer for b. Part (a) of the figure below gives the magnitude E(x) of the electric fields that have been set up by a battery along a resistive rod of length 9.00 mm (part (b) of the figure). The vertical scale is set by Es = 7.20 times 103 V/m. The rod consists of three sections of the same material but with different radii. (The schematic diagram of part (b) of the figure does not indicate the different radii.) The radius of section 3 is 5.20 mm.

Explanation / Answer

given length of wire = L = 9mm length of every section = L = l/3 let r1, r2 and r3 be the radii of three respective parts where r3 = 5.2mm vertical scale E = 7.20 * 10^3 V/m from the current density J = i/A = E/? AE = i? A) since i& ? are constant so A1E1 = A2E2= A3E3 A1E1 = A3E3 ?r12E1 = ?r32 E3 r12 = E3/E1)r32 = (3.744 * 10^3/3.456 * 10^3) ( 5.2 mm)2 r1 = 5.63mm B) A2E2= A3E3 ?r22E2 = ?r32 E3 r22 = E3/E2)r32 = (3.744 * 10^3/7.2 * 10^3) ( 5.2 mm)2 r2 = 2.70mm    given length of wire = L = 9mm length of every section = L = l/3 let r1, r2 and r3 be the radii of three respective parts where r3 = 5.2mm vertical scale E = 7.20 * 10^3 V/m from the current density J = i/A = E/? AE = i? A) since i& ? are constant so A1E1 = A2E2= A3E3 A1E1 = A3E3 ?r12E1 = ?r32 E3 r12 = E3/E1)r32 = (3.744 * 10^3/3.456 * 10^3) ( 5.2 mm)2 r1 = 5.63mm B) A2E2= A3E3 ?r22E2 = ?r32 E3 r22 = E3/E2)r32 = (3.744 * 10^3/7.2 * 10^3) ( 5.2 mm)2 r2 = 2.70mm    r1 = 5.63mm B) A2E2= A3E3 ?r22E2 = ?r32 E3 r22 = E3/E2)r32 = (3.744 * 10^3/7.2 * 10^3) ( 5.2 mm)2 r2 = 2.70mm    r2 = 2.70mm   

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