Dim Bulb
Electricity and Magnetism
Level
2
What will be the current running through an incandescent light bulb that is marked when it is connected to a voltage source of ?
0.5
4
1
2
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1 solution
While Ohm's law formula I[A]=P[W]/U[V] is correct, the light bulb's power rating of 220 [W] only holds when it is connected to its rated voltage of 220[V]. Therefore it is incorrect to use the formula I [A]= 220[W]/110[V]= 2[A]. Rather one must compute the bulb's resistance from its rated parameters: R[ohm]= U squared/P= 48400/220= 220 [ohm]. Then, when connected to a voltage source of 110 [V], the current will be I=110[V]/220[ohm]=0.5[A].