Two equal resistances when connected in series to a battery,
Question:

Two equal resistances when connected in series to a battery, consume electric power of $60 \mathrm{~W}$. If these resistance are now connected in parallel combination to the same battery, the electric power consumed will be :

  1. (1) $60 \mathrm{~W}$

  2. (2) $240 \mathrm{~W}$

  3. (3) $120 \mathrm{~W}$

  4. (4) $30 \mathrm{~W}$


Correct Option: , 2

Solution:

(2) When two resistances are connected in series,

$R_{e q}=2 R$

Power consumed, $P=\frac{\varepsilon^{2}}{R_{e q}}=\frac{\varepsilon^{2}}{2 R}$

In parallel condition, $R_{e q}=R / 2$.

New power, $\mathrm{P}^{\prime}=\frac{\varepsilon^{2}}{(\mathrm{R} / 2)}$

or $\mathrm{P}^{\prime}=4 \mathrm{P}=240 \mathrm{~W} \quad(\because \mathrm{P}=60 \mathrm{~W})$

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