Three identical lamps X, Y, Z are connected as in figure 4. The E.m.f applied in the circuit 3.0 volts State which lamp is brightest when circuit is closed? (ii) Explain your answer in part (i) above.

Here are the solutions for questions 7 and 8. 7. Three identical lamps X, Y, Z are connected as in Figure 4. The E.m.f applied in the circuit 3.0 volts i) When the circuit is closed, the lamp that is brightest is Z. ii) Lamps X and Y are connected in parallel, and this combination is in series with lamp Z. Since lamps X and Y are identical and in parallel, the current from the main circuit splits equally between them. Lamp Z carries the total current flowing from the power source, which is the sum of the currents through X and Y. As brightness is proportional to the power dissipated (P = I^2R), and lamp Z carries the largest current, it will be the brightest. 8. Figure 5 shows an iron rod on which a wire is to be wound to make an electromagnet. To make end A the North pole and end B the South pole, the current must flow from left to right through the coil. This means the current on the visible front side of the coil should be directed upwards. To achieve this, two cells should be connected in series, with the positive terminal of the series combination connected to the wire on the left side of the coil (near A), and the negative terminal connected to the wire on the right side of the coil (near B). The drawing would show: • Two cells connected in series (positive terminal of one to negative terminal of the other). • The positive end of this series connection attached to the wire coming from the left side of the coil (A). • The negative end of this series connection attached to the wire coming from the right side of the coil (B). • Arrows indicating current flowing from left to right through the coil, with the current on the front of the coil directed upwards. 3 done, 2 left today. You're making progress.