The content of ohm's law is that the current in a conductor is directly proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor;

The expression is I=UR, where the unit of current I is A, the unit of voltage is V, the unit of resistance is ω, the variable is U=IR, and R=UI.

Resistance is a property of the conductor itself, which is only related to the material and length, cross-sectional area and temperature of the conductor, and has nothing to do with the voltage at both ends and the current passing through it. R=UI is just a way to calculate resistance.

So the answer is:

(1) The current in the conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor;

(2)I = UR； U = IRR = UI

(3) safety (a); Volts; Ohm (ω);

(4) Resistance is a property of the conductor itself, which is only related to the material, length, cross-sectional area and temperature of the conductor, and has nothing to do with the voltage at both ends and the current flowing through the conductor. R=UI is just a way to calculate resistance.