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Question

An inductor of reactance \(1~\Omega\) and a resistor of \(2~\Omega\)are connected in series to the terminals of a \(6~𝑉(π‘Ÿπ‘šπ‘ )\) AC source.
The power dissipated in the circuit is:

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Solution

Formula used:

\(𝑃=𝑉_{π‘Ÿπ‘šπ‘ } 𝐼_{π‘Ÿπ‘š}~ π‘π‘œπ‘ β‘\phi=𝑉_{π‘Ÿπ‘šπ‘ } 𝐼_{π‘Ÿπ‘šπ‘ }\dfrac{ 𝑅}{𝑍}\)

Given,

Inductive reactance, \(𝑋_{l}=1~\Omega\)

Capacitive reactance, \(𝑋_{𝐢}=0\)

Resistance, \(𝑅=2~ \Omega\)

Rms voltage, \(𝑉_{π‘Ÿπ‘šπ‘ }=6~ 𝑉\)

As we know, Impedance of the circuit,

\(𝑍=\sqrt{𝑋_{𝐿}^{2}+𝑅^{2}}=\sqrt{(1)^{2}+(2)^{2}}\)

\(𝑍 =\sqrt{5}~ \Omega\)

The average power dissipated by resistor (power is never dissipated by inductor or capacitor) of resistance 𝑅 in any ac circuit with π‘Ÿπ‘šπ‘  current \(𝐼_{π‘Ÿπ‘šπ‘ }\) is given by,

\(𝐼_{π‘Ÿπ‘šπ‘ }=\dfrac{𝑉_{π‘Ÿπ‘šπ‘ }}{𝑍}=\dfrac{6}{\sqrt{5}} ~𝐴\)

Power dissipated,

\(𝑃=𝑉_{π‘Ÿπ‘šπ‘ } 𝐼_{π‘Ÿπ‘š}~ π‘π‘œπ‘ β‘\phi=𝑉_{π‘Ÿπ‘šπ‘ } 𝐼_{π‘Ÿπ‘šπ‘ }\dfrac{ 𝑅}{𝑍}\)

\(𝑃=6\times\dfrac{6}{\sqrt{5}}\times\dfrac{2}{\sqrt{5}}=\dfrac{72}{5}=14.4 ~π‘Š\)

Final Answer: Option (c)

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