The fact that, in general, liquids and gases expand when heated gives rise to
a) convection currents in fluids due to changing masses.
b) convection currents in fluids due to changing densities.
c) heat transfer by conduction.
d) convection currents in fluids due to constant temperatures,

Cells in the nervous system have a potential difference of 70 mv across the cell membrane separating the interior of the cell from the extracellular fluid. this potential difference is maintained by ion pumps that move charged ions across the membrane. is this an emf? select the correct answer and explanation. 1)no. the ion pumps cannot separate charges; thus, they cannot create a potential difference. 2)yes. the ion pumps cannot separate charges, but they still can create a potential difference. 3)yes. the ion pumps can actively separate charge; thus, they can create a potential difference. 4)no. the ion pumps can separate charges, but they cannot create a potential difference.