1. The problem statement, all variables and given/known data I did a photoelectric experiment using the PASCO Model AP-9368 mercury lamp. The stopping potential I got was very low: 1.476V for ultra violet, 1.303V for violet, 1.181V for blue, 0.788V for green and 0.707V for yellow. And the Plansk's constant I got from this set of values was about 4.005e-34J.s which is nowhere close than the 6.626e-34J.s But when I did this experiment again about four days later, the stopping potential values I got changed: I got 1.964V for ultra violet, 1.686V for violet, 1.488V for blue, 0.840V for green and 0.728V for yellow. And this time the Planck's constant was 6.184e-34J.s which is better. And after another two days when I did it again, the stopping potential values changed again to the lower ones. I checked the battery for the apparatus and the battery level was the same all three times. Could anyone please give me an idea why this is happening? I'm so confused? Thanks!