Question

Laxmi and her mother went ot the market to purchase some household articles. Laxmi's mother was goind to purchase $100W$ bulb. Laxmi advised to purchase a CFL. She told her mother about the advantage of CFL.
(a) What quality do you notice in laxmi?
(b) A $100W$ bulb and a $250W$ bulb joined in series to ac mains. Which bulb will consume more power>

Answer 1

$\left(a\right)$

Laxmi has quality of energy saver.

$\left(b\right)$

we know $power=V^2/Resistance$ so for bulb having more $power\left(250W\right)$ will have $less$ resistance.

But in series the voltage is different in different bulbs so we will use formula $power=I^2\times Resistance$ according to which the bulb having more resistance$\left(100W\right)(more-resitance)$ will consume more power so the $first$ bulb will consume more power because it has more resistance but this time it will not consume 100W because voltage across it is different from the rated voltage.

Note-

When electric appliances are sold the have rating on them considering that they will be used in parallel combination i.e. all component in home are made for $220V.$