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December 2004


Lamp intensity

This time consider the circuit in Figure 1. Lamps La1 and La2 each have a nominal power P = 1 watt. Lamp La1 has an internal resistance of R1 = 100 Ohm while for lamp La2, R2 = 200 Ohm. Both resistance values are applicable at the nominal lamp power. The alternating voltage source show supplies a voltage U = 22.63 V at a frequency of 50 Hz. The value of capacitor C is such that the component also represents a reactance of 200 Ohm at 50 Hz, in other words, C has a value of 15.915 µF. Initially, switch is opened (as shown in the diagram) and the voltage source supplies a voltage U causing lamp La1 to be supplied with current and the lamp to light at a certain intensity. Next, switch S is closed, which leads us to the question: After closing the switch, will the intensity of lamp La1 increase, decrease or remain the same? Followed by a second question: After closing the switch, which of the two lamps La1 and La2 lights brighter?

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