Two bulbs when connected in parallel to a source take 100 w each. the total power consumed when they are connected in series with the same source is
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There are many answers to this questions and all are correct. So, I wont discuss the solution to the problem but the confusion between the two relations for power, i.e., P = I^2. R and P = VI.
Assuming the power across one bulb is P.
P = I^2. R = VI
When we are using P = I^2. R
The current through the resistors when connected in series will be 0.5 times that when in parallel for a single bulb.
So, power consumed = (0.5 I)^2. R = 0.25 I^2. R = 0.25 P
When we are using P = VI
In case of series connection of resistors, the voltage gets divided in the ratio of the resistance. So, voltage across a bulb = 0.5 times of that in parallel connected bulbs. The current is also 0.5 times as we saw earlier.
So, power consumed = (0.5)V*(0.5)I = 0.25 VI = 0.25 P
It can be seen that we got the same result by both the formulas.
Note : The voltage across the resistance is considered not the supply voltage!!!
Assuming the power across one bulb is P.
P = I^2. R = VI
When we are using P = I^2. R
The current through the resistors when connected in series will be 0.5 times that when in parallel for a single bulb.
So, power consumed = (0.5 I)^2. R = 0.25 I^2. R = 0.25 P
When we are using P = VI
In case of series connection of resistors, the voltage gets divided in the ratio of the resistance. So, voltage across a bulb = 0.5 times of that in parallel connected bulbs. The current is also 0.5 times as we saw earlier.
So, power consumed = (0.5)V*(0.5)I = 0.25 VI = 0.25 P
It can be seen that we got the same result by both the formulas.
Note : The voltage across the resistance is considered not the supply voltage!!!
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Power consumed when connected in series is 0.25Watt
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