Comprehension

In the circuit, a metal filament lamp is connected in series with a capacitor of capacitance $C\, \mu F$ across a $200\, V , 50\, Hz$ supply. The power consumed by the lamp is $500\, W$ while the voltage drop across it is $100\, V$. Assume that there is no inductive load in the circuit. Take $r m s$ values of the voltages. The magnitude of the phase-angle (in degrees) between the current and supply voltage is $\phi $. Assume, $\pi \sqrt{3} \approx 5$

Question: 1

The value of C is ___.

Updated On: May 25, 2024
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Correct Answer: 100

Solution and Explanation

\(P = \frac{V^2}{2}\)

\(⇒\) \(500 = \frac{100^2}{R}\)

\(⇒ R = 20 Ω\)

Now across resistance 500 = I × 100

\(⇒\) I rms = 5 A

Vrms = 200 V,

\(\frac{V_{\text{rms}}}{\text{real}} = 100 \, \text{V}\)

\(\cos \varphi = \frac{100}{200} = \frac{1}{2} \quad \Rightarrow \quad \varphi = 60^\circ\)

\(\tan \varphi = \frac{X_C}{R} = \frac{1}{\omega RC}\)

\(\sqrt{3} = \frac{1}{100\pi(20)C}\)

\(C = \frac{1}{{20\pi\sqrt{3} \times 100}}\)

\(C = 10^{-4} \, \text{F}\)

\(= 100 μF\)

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Question: 2

The value of 𝜑 is ___.

Updated On: May 23, 2024
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Correct Answer: 60

Solution and Explanation

\(P = \frac{V^2}{2}\)

\(⇒\) \(500 = \frac{100^2}{R}\)

\(⇒ R = 20 Ω\)

Now across resistance 500 = I × 100

\(⇒\) I rms = 5 A

Vrms = 200 V,

\(\frac{V_{\text{rms}}}{\text{real}} = 100 \, \text{V}\)

\(\cos \varphi = \frac{100}{200} = \frac{1}{2} \quad \Rightarrow \quad \varphi = 60^\circ\)

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