Suppose you wish to fabricate a uniform wire from a mass m of a metal with density rhom and resistivity rho. if the wire is to have a resistance of r and all the metal is to be used, what must be the length and the diameter of this wire? (use any variable or symbol stated above as necessary.

Name three different units of energy used to measure heat and describe what type of situations each is usually used.

Explain why electric current cannot exist if a current doesn't have a voltage source.

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.