Two identical resistors with resistances 15 ohm are connected in series and parallel to a battery of 6 V. Calculate ratio of power consumed.

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In order to calculate the ratio of the power consumed in the combination of resistors in each case, we have to:

Resistance of two identical resistors, R1 = R2 = 15Ω

Voltage of battery, V = 6V.

Now, in order to determine the ratio of power that is consumed in the combination of resistors in each case, PS/PR.

  1. In case of Series combination

In series, total resistance can be represented as:

RS = R1 + R2

After replacing the values,

⇒ RS = 15 + 15

⇒ RS = 30Ω

Therefore, total resistance in series, RS is 30Ω 

Now, we are already aware that the power consumed by a resistor can be denoted as:

Power = Voltage2/Resistance 

Or,  

P = V2/R

Thus, Replacing the values of V and R, we can obtain:

PS = 62/30

⇒ PS = 36/30

⇒ PS = 1.2W

Hence, the power that is consumed in series, PS is 1.2 watt.

  1. In case of Parallel combination: 

In a parallel combination, the total resistance can be given as:

1/RP = 1/R1  + 1/R2 

After replacing the values,

⇒ 1/RP  = 1/15 + 1/15

⇒ 1/RP  = 1 + 1/15

⇒ 1/RP  = 2/15

⇒ RP  = 15/2

⇒ RP  = 7.5Ω

Therefore, effective resistance in parallel combination, RP is 7.5Ω.

Now, we are already aware that the power consumed by a resistor is expressed as:

Power = Voltage2/Resistance Or,  P=V2/R

Replacing the values of V and R, we can obtain:

PR = 62/7.5

PR = 36/7.5

PR = 360/75

PR = 4.8W

Hence, power consumed in a parallel combination, PR is 4.8 watt

With the given data, the ratio of power consumed in the two combinations will be,

PS/P= 1.2 W/4.8

Hence, W = 1/4 = 1:4 

Therefore, ratio of power consumed in the combination of resistors in both cases is 1:4.


Related Questions

  1. X and Y, that are two resistors, with resistances of 2 Ω and 3 Ω respectively are first connected in parallel and then in series. In both cases, the voltage that is supplied is 5 V. (i) Illustrate a circuit diagram to show the combination of resistors. (ii) Calculate amount of voltage across 3 Ω resistor in the series combination of resistors.
  2. A Circuit Consists Of A Battery Of 3 Cells (2 V Each), A Combination Of Three Resistors, 10 Ohm, 20 Ohm And 30 Ohm, Attached Parallelly, With Plug Key And Ammeter (In Series).

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                          CBSE CLASS XII Previous Year Papers

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