An electric heater has two power settings. One setting is 0.5 kW and the other is 1.5 kW. One kWh of electricity costs 11 pence. Calculate how much you would save if you used the heater 12 hours on the 0.5 kW setting instead of the 1.5 kW setting.

Students in an introductory physics lab are performing an experiment with a parallel-plate capacitor made of two circular aluminum plates, each 11 cm in diameter, separated by 1.0 cm. how much charge can be added to each of the plates before a spark jumps between the two plates? for such flat electrodes, assume that value of 3×106n/c of the field causes a spark.