An experimental setup of verification of photoelectric effect is shown if Fig. The voltage across the electrodes is measured with the help of an ideal voltmeter, and which can be varied by moving jockey J on the potentiometer with wire. The battery used in potentiometer circuit is of 20 V and its internal resistance is 2 Omega. The resistance of 100cm long potentiometer wire is 8 Omega. The photocurrent is measured with the help of an ideal ammeter. Two plates of potassium oxide of area 50 cm^2 at separation 0.5mm are used in the vacuum tube. Photocurrent in the circuit is very small, so we can treat the potentiometer circuit as an independent circuit. The wavelength of various colors is as follows: Q. When radiation falls on the cathode plate, a current of 2muA is recorded in the ammeter. Assuming that the vacuum tube setup sollows Ohm's law, the equivalent resistance of vacuum tube operating in this case when jockey is at end P is