Physics I / Current, Resistance, and DC Circuits
Practice question · Multiple choice

Two bulbs: a 60 W and a 100 W (both rated for mains voltage). You connect them in series across the mains. Which bulb glows brighter?

Hints
  1. From P=V2/RP = V^{2}/R at rated voltage: which bulb must have the higher resistance?
  2. In series the current II is identical, so compare P=I2RP = I^{2}R, power now grows with RR.
Show the answer

C. The 60 W bulb: larger resistance, shared current

Why

The 60 W bulb has the larger filament resistance (R=V2/PR = V^{2}/P). In series, both carry the same current, and P=I2RP = I^{2}R favours the larger RR, so the "weaker" bulb wins. Power ratings only apply in the circuit they were rated for.

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