Tuesday, 8 January 2008 - 9:39 PM EST
1) the 100 W bulb draws more current because P = IV, therefore P/V = I, so Current is directly proportional with power. However, the 75 W bulb would have more resistance because R = V^2/P, so power is inversely proportional to Resistance.
2) If the 15A fuse blows, it means that too much current is passing through the circuit for the wiring to handle without overheating. With a 25 amp fuse, the wiring would be able to overheat because the fuse would blow at a higher current, thereby causing a major fire hazard.
3) with a series circuit the christmas tree lights would have an equal current all the way through, so the fuse can't blow, but have more resistance so they may be dimmer. A parallel circuit would have less resistance, meaning brighter light given off, however, current would be the sum of currents from all of the junctions, meaning a higher current, which could short out the lights