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In the below circuit diagram, calculate the power consumed in the circuit when:

(a) the switch S1 is closed, and the switch S2 is open.

(b) the switch S2 is closed, and the switch S1 is open.

In the below circuit diagram, calculate the power consumed in the circuit when: Physics Competency Focused Practice Questions Class 10 Solutions.

Household Circuits

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Answer

(a) When switch S1 is closed, and the switch S2 is open.

Here, 60 Ω and 20 Ω are in parallel

Let total resistance of circuit in this condition = R1

So, by formula

1R1=160+1201R1=1+360R1=604R1=15 Ω\dfrac{1}{\text R1} = \dfrac{1}{60} + \dfrac{1}{20} \\[1em] \dfrac{1}{\text R1} = \dfrac{1+3}{60} \\[1em] \text R1 = \dfrac{60}{4} \\[1em] \text R1 = 15\ Ω

Power consumed = V2R1=5×515=53=1.67 W\dfrac{{\text V}^2}{R_1}=\dfrac{{}5 \times 5}{15} = \dfrac{5}{3} =1.67 \text{ W}

(b) When switch S2 is closed, and the switch S1 is open.
Here, negligible current flows through the 60 Ω resistor because the majority of the current takes the path of least resistance, which includes the 20 Ω resistor. Therefore, most of the current flows through the 20 Ω path.
So, total resistance of circuit R2 = 20 Ω

Power consumed = V2R2=5×520=54=1.25 W\dfrac{{\text V}^2}{R_2}=\dfrac{{}5 \times 5}{20} = \dfrac{5}{4} =1.25 \text{ W}

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