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Physics · 2023 · 3 marks
CBSE 2023 · Region 2 · Set 1 · Q28
A series CR circuit with R =200 Ω and C =(50 / π) μ F is connected across an ac source of peak voltage ε_0=100 V and frequency v=50 Hz. Calculate (a)…
A series CR circuit with $\displaystyle \mathrm{R}=200 \Omega$ and $\displaystyle \mathrm{C}=(50 / \pi) \mu \mathrm{F}$ is connected across an ac source of peak voltage $\displaystyle \varepsilon_{0}=100 \mathrm{~V}$ and frequency $\displaystyle v=50 \mathrm{~Hz}$. Calculate
(a)
impedance of the circuit (Z), (b) phase angle ( $\displaystyle \phi$ ), and (c) voltage across the resistor.
Marking-scheme solution
Calculating\[\text { (a) } \begin{aligned}
& Z=\sqrt{\mathrm{R}^{2}+X_{c}^{2}}==\sqrt{\mathrm{R}^{2}+\left(\frac{1}{2 \pi v \mathrm{C}}\right)^{2}} \\
& X_{c}=\frac{1}{2 \pi v \mathrm{C}}=\frac{1}{2 \times \pi \times 50 \times \dfrac{50}{\pi} \times 10^{-6}}=200 \Omega \\
& Z=\sqrt{(200)^{2}+(200)^{2}}=200 \sqrt{2} \Omega \\
& \approx 282 \Omega
\end{aligned}
\]
\[\text { (b) } \begin{aligned}
\tan \phi & =\frac{X_{c}}{\mathrm{R}}=\frac{200}{200} \\
\phi & =45^{0} \quad \text { or } \frac{\pi}{4} \mathrm{rad}
\end{aligned}
\]
\[\text { (c) } \begin{aligned}
V_{r m s} & =I_{r m s} \mathrm{R}=\frac{V_{r m s}}{Z} \mathrm{R} \\
& =\frac{100}{\sqrt{2} \times 200 \sqrt{2}} \times 200 \\
& =50 \mathrm{~V}
\end{aligned}
\]
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