1. The problem statement, all variables and given/known data The filament of the lamp in X breaks and the lamp no longer conducts. It is observed that the voltmeter reading decreased and the lamp Y glows more brightly. a) Explain without calculation why the voltmeter reading decreases. b) Explain without calculation why the lamp Y glows more brightly. 2. Relevant equations R = V/I (R = resistance, V = voltage, I = current) 3. The attempt at a solution I've thought of two explanations to why the voltmeter reading decreases. But I don't know which is the right one, or whether both are perfectly legit explanations: 1) Current now has to flow through one route (before the lamp at X broke, there were two routes), so resistance at the top branch (where lamp Y is) will increase. The whole circuit is now in series, which means that the battery's voltage will be divided up in accordance with the ratio of resistance between the two resistors. Because resistance at where lamp Y is has increased, this means that it will now take a larger share of the voltage, leaving less for the resistor where the voltmeter is placed at. 2) Before lamp X broke, there was a parallel circuit, current would've had to split off. Now that's gone, current flowing through lamp Y must be greater than what it was before. Hence using the R = V/I, we can figure out voltage for this part of the circuit will have increased, and because the battery's voltage hasn't changed, this must mean that theres less voltage at where the volt-meter is placed at. Basically I'm not sure whether it is resistance OR current at the top branch (where lamp Y and resistor R2 is placed at) which has increased. To be honest, I'm not sure exactly what the rectangular box symbols mean, I know they are resistors, but I don't know if they are 'fixed' which means they'll produce the same resistance regardless of any other changes made in the circuit (if so, then that would suggest it is current which increases, not resistance) and to complicate things further, do the lamps have resistance? (obviously in reality yes, but I'm not sure whether the question has simplified things - please note this isn't university level, this from an AQA A-level physics past paper) because if they do, the fact that lamp X has gone, would surely affect the amount of current flowing through the circuit (I = V/R).