Calculate the power used in the 2 Ω resistor in each of the following circuits:

(i) a 6V battery in series with 1 Ω and 2 Ω resistors.


(ii) a 4 V battery in parallel with 12 Ω and 2Ω resistors.

(a) Here V = 6 volt, R1 = 1 ohm, R2 = 2 ohm

The connection is in series. So Equivalent resistance = R1+R2 = 1 + 2 = 3 ohm


We know that


Total current I = V/R = 6/3 = 2A


Current through R2 = I2 = I = 2A


Voltage across R2 = V2 = I2R2 = 2×2 = 4 ohm


Power used in R2 = I2V2 = 2×4 = 8W


(b) Here, V = 4 volt,R1 = 12 ohm, R2 = 2 ohm


We know that, as the connection is in parallel so voltage across R2 = V2 = V = 4V


Current across R2 = I2 = V2/R2 = 4/2 = 2A


As power = IV


Power used in R2 = I2V2 = 2×4 = 8W


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