A wire made from copper with a cross-section of diameter 0.730 mm carries a curr

Question

A wire made from copper with a cross-section of diameter 0.730 mm carries a current of 11.0 A. Calculate the "areal current density"; in other words, how many electrons per square meter per second flow through this wire? (Enter your answer without units.)

The density of copper is 8.97 g/cm3, and its atomic mass is 63.7. Assuming each copper atom contributes one mobile electron to the metal, what is the number density of free charges in the wire, in electrons/m3? (Enter your answer without units.

Explanation / Answer

Here ,

in series ,

the total capacitance is

1/Ceq = 1/2.75 + 1/5.90

Ceq = 1.875 uF

Energy stored = 0.5 * CV^2

Energy stored = 0.5 * 1.875 *10^-6 * 21^2

Energy stored = 4.136 *10^-4 J

Now, In parallel

Ceq = 2.75 + 5.90

Ceq = 8.65 uF

for same energy

4.136 *10^-4 =0.5* 8.65 *10^-6 * V^2

V = 9.8 V

the battery needed is 9.8 V

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