1. Consider two light bulbs, A and B. The laments in both are the same length an

Question

1. Consider two light bulbs, A and B. The laments in both are the same length
and made of the same material but lament A is thicker than lament B. If they
are plugged into the same voltage, which bulb will be brighter?
2. Bulb C is rated 0 Watts" in the U.S. where the common voltage is 120 V.
What power would it produce if plugged into 240 V as is common in Europe?
Neglect the temperature dependence of resistivity.
3. How would your answer to question 2 change if you do not neglect the
temperature dependence of resistivity? (The laments are ordinary" laments;
they are neither semiconductors nor superconductors.)

Explanation / Answer

a) A reason : as A is thicker, its resistance is less and hence it dissipates more power (P=V^2/R) b) R = V^2/P NOW, V' = 2V P' = V'^2/R = = 4V^2/R = 4P = 4*60 = 240 W c) P' = 4V^2/R but R will increase with increase in temperature hence power will be a little less than 240 W

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