The figure shows the principle circuit diagram of measuring the DC resistance of the coil. The known internal resistance of the voltmeter is 2kΩ. If after the measurement is completed , the switch K is suddenly turned on, the maximum voltage that the voltmeter can withstand is________V. Choose A,B,C or D. In the steady state of DC circuit, the inductance is treated as short wire. So before the switch K is turned on, this circuit is equal to the circuit consisted of one direct voltage and two resistors. After the swith K is suddenly truned on ,the inductor can be treated as a current source of 2/(8+2) A, there exists a loop circuit consisted of the indcutor, the resistor 2 Ω and the voltage meter. So the inductor will release the magnetic field energy through the loop , at last there is no current in the loop. So the maximum voltage of the voltage meter can withstand is equal to the current in the loop circuit times the internal resistor 2kΩ.