Power in Circuits Video Lessons

Concept

# Problem: Two light bulbs use 30 W and 60 W, respectively, when connected in parallel to a 120-V source. How much power does each bulb use when connected in series across the 120-V source, assuming that their resistances remain the same?

###### FREE Expert Solution

Power is expressed as:

$\overline{){\mathbf{P}}{\mathbf{=}}\frac{{\mathbf{V}}^{\mathbf{2}}}{\mathbf{R}}}$

Therefore, R = V2/P

For the 30W bulb, R30 = (120)2/30 = 480Ω

For 60W bulb, R60 = (120)2/60 = 240Ω

Curent, i = V/R

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###### Problem Details

Two light bulbs use 30 W and 60 W, respectively, when connected in parallel to a 120-V source.

How much power does each bulb use when connected in series across the 120-V source, assuming that their resistances remain the same?