a).Considering a particular metal wire with resistivity ? = 30 x 10-9 Om and cur

Question

a).Considering a particular metal wire with resistivity ? = 30 x 10-9 Om and current density J = 1.34 x 106 A/m2, what is the potential difference over 127 m of the wire?

Express the result in the unit [V] and to three significant figures. If you must use scientific notation, please enter as follows: e.g. 0.000123 = 1.23E-4. Only answer in numerical values, no units. For negative numbers, leave no space between the negative sign and the number: e.g. right: -1.00, wrong: - 1.00.

b).A person notices a mild shock if the current along a path through the thumb and index finger of one hand exceeds 80 µA. Calculate the maximum allowable potential for a hand with moist skin with a resistance of 85.9 kO.

Express the result in the unit [V] and to three significant figures. If you must use scientific notation, please enter as follows: e.g. 0.000123 = 1.23E-4. Only answer in numerical values, no units. For negative numbers, leave no space between the negative sign and the number: e.g. right: -1.00, wrong: - 1.00.

Explanation / Answer

a) we have

 

=30x10^-9m

 

J=1,34x10^6A/m^2

 

l=127m

 

 

 

also

 

R=l/A

 

l  is the cable length  and  A he area of cross section

 

J=I/A

 

determine  V by law ohms V=IR

 

 

 

solving I=JA     THEN   V=(JA)*(l/A)

 

V=J*l

 

V=1,34x10^6A/m^2 *30x10^-9m*127m

 

V=5,105

 

 

 

b)

 

We  have

 

I=80A

 

R=85,9k

 

by law ohms  V=IR

 

V=80x10^-6A*85,9x10^3

 

V=6,872 V

 

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