Well the p.d of the resistor was 1,6 V u don't include the e.m.f because some volatge was used by the internal resistance regardless. The internal resistor is kind of like a second resistor in the circuit. So ya 4. something was the right answer. Also plancks constant was calculated by using W=QV of an electron and then equating it to E=hf. Then ya perecantage uncertanity and such and it was off by like 10% for me