A nerve signal is transmitted along the long, thin axon of a neuron in a small fish. The transmission occurs as sodium ions (Na+)transfer like tipping dominos across the axon membrane from outside to inside. Each short section of axon gets an excess of about 6.0×108sodiumions/mm.

Determine the E field 4.0 cm from the axon produced by the excess sodium ions on the inside of the axon and an equal number of negative ions on the outside of a 1.0-mm length of axon. The ions are separated by the 8.0×10−9-m-thick axon membrane. Use κ = 81 for the dielectric constant of water.