First slide

Thermal effect of current

Question

Electric bulb 50 W-100V glowing at full power are to be used in parallel with battery 120 V, 10 $Ω$ . Find maximum number of bulbs that can be connected so that they glow in full power.

Moderate

Solution

When each bulb is glowing at full power,
Current from each bulb $i = \frac{P}{V} = \frac{50}{100} = \frac{1}{2} A$
So main current $i = \frac{n}{2} A$
$Also E = V + i r$
$\Rightarrow 120 = 100 + (\frac{n}{2}) \times 10$
$\Rightarrow n = 4$

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