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voltage drops















        What is the resistance of such a                        The resistance of an incandes-

        10W/12V light bulb? It doesn't                          cent lamp can also not be deter-
        make sense to measure the re-                           mined with Ohm's law, because

        sistance with an ohmmeter, be-                          the resistance depends on the

        cause the resistance of the light                       temperature of the filament and
        bulb will change once current                           is therefore not linear. We have

        passes through it. The filament                         determined the resistance of the

        will become very hot, and it will                       incandescent lamp in our lab

        have a higher resistance value                          by switching 12 V over the bulb
        than cold.                                              with a stabilized power supply

                                                                and see how much current flows

                                                                through it. The current is 0.87 A.
                                                                With Ohm's law we can deter-

                                                                mine the resistance of our incan-

                                                                descent lamp:




                                                                      Rbulb= U/I = 12V/0,87A














                                                                                               13,8 Ω






                                                         12V









                            Paruzzi Magazine 23                                                                 9



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