A cylindrical wire of radius \( 0.5 \, \text{mm} \) and conductivity \( 5 \times 10^{7} \, \text{S/m} \) is subjected to an electric field of \( 10 \, \text{mV/m} \). The expected value of current in the wire will be \( x^{3}\pi \, \text{mA} \). The value of \( x \) is ________.