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Answer 1 · 2015-10-15T16:12:22

60W lamp is brighter.

Suposing both lamps are designed to operate with the same voltage, as 220V:

The resistance of the 60W lamp is:

$R = \frac{v^{2}}{P}$ $R = v^2/P$ = $\frac{220^{2}}{60}$ $220^2/60$ = 806,67 Ohms

The resistance of the 250W lamp is:

$R = \frac{220^{2}}{250}$ $R = 220^2/250$ = 193,6 Ohms

If we connect both in series at a 220V mains, the current will be:

I = $\frac{220}{806, 67 + 193, 6}$ $220/(806,67 +193,6)$ = 0,22 A

As far as Power = $R \cdot I^{2}$ $R*I^2$ ,

The power dissipated by the 60W lamp is:

P(60) = $806, 67 \cdot 0, 22^{2}$ $806,67*0,22^2$ = 39W

And the power dissipated by the 250W lamp is:

P(250) = $193, 6 \cdot 0, 22^{2}$ $193,6*0,22^2$ = 9,37W

So, the 60W lamp will be brighter.