To calculate the current using Ohm's Law, we can use the formula:
\[ I = \frac{V}{R} \]
Where:
- I is the current,
- V is the potential difference (voltage),
- R is the resistance.
In this case, the potential difference (V) is given as 81 mV, which we can convert to volts by dividing by 1000:
\[ V = 81 \, \mathrm{mV} = 81 \times 10^{-3} \, \mathrm{V} \]
The resistance (R) is given as \( 4.3 \times 10^9 \, \Omega \).
Now we can substitute these values into the formula to calculate the current (I):
\[ I = \frac{81 \times 10^{-3} \, \mathrm{V}}{4.3 \times 10^9 \, \Omega} \]
To simplify the calculation, we can divide the numerator and denominator by \( 10^{-3} \):
\[ I = \frac{81}{4.3 \times 10^9} \, \mathrm{A} \]
Thus, the current when the potential difference between the walls is 81 mV is approximately \( \frac{81}{4.3 \times 10^9} \) Amperes.