At what voltage is a 2kΩ resistor if a current of 0.3A flows through it.

According to Ohm’s law, the current in the rheostat will be directly proportional to the voltage on the rheostat and inversely proportional to the resistance of the rheostat.
I = U / R, where I is the current in the rheostat (I = 0.3 A), U is the voltage across the rheostat (V), R is the resistance of the rheostat (R = 2 kΩ = 2 * 10 ^ 3 Ohms).
Let us express and calculate the voltage across the rheostat:
U = I * R = 0.3 * 2 * 10 ^ 3 = 600 V.
Answer: The voltage across the rheostat is 600 V.