Answers

2015-07-05T23:54:29+05:30
1. I suppose you meant 1mA, please be very careful in writing units, mA means milli Amperes, MA means Mega Amperes, which is very unusual. So the answer below assumes mA or milli amperes.

1 Ampere = 1 Coulomb per 1 second, so if 1 Ampere flows for 1 second, charge transferred is 1 Coulomb

For given problem, current = 1 * 10^-3 Amperes
Time = 30 * 60 = 1,800 seconds
so Charge = 1 * 10 ^-3 * 1800
= 1.8 Coulombs ... Answer

2. Resistance = Rho * l / A (Rho = resistivity, l = length, A = Area)
So Length l - R * A / Rho
= 5 *  \pi * 1 ^2 / 4 / 0.8 * 10^-8
= 4.91 * 10^8 mm
= 491 km.. Answer


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