Answer:
[tex]P'=\dfrac{P_1P_2}{P_1+P_2}[/tex]
Explanation:
Lets take
Resistance of bulb 1 =R₁
Resistance of bulb 2 =R₂
As we know that power P
P= ΔV²/R
Given that voltage difference is same for both bulbs
So
P₁R₁= ΔV² --------1
P₂R₂= ΔV² -----------2
When these resistance are connected in series then equivalent resistance R
R=R₁+ R₂
The new power P'
P'=ΔV²/R
P'R=ΔV² ------3
From equation 1 ,2 and 3
P'(R₁+ R₂) = ΔV²
[tex]P'\left(\dfrac{\Delta V^2}{P_1}+\dfrac{\Delta V^2}{P_2}\right)=\Delta V^2[/tex]
[tex]P'=\dfrac{P_1P_2}{P_1+P_2}[/tex]