CBSE 2025 · Region 6 · Set 2 · Q33 · 5 marks
(i)Write the principle of working of an ac generator. Draw its labelled diagram and explain its working.(ii)A resistor of $\displaystyle 400 \Omega$, an inductor of $\displaystyle \left(\frac{5}{\pi}\right) \mathrm{H}$ and a capacitor of $\displaystyle \left(\frac{50}{\pi}\right) \mu \mathrm{F}$ are joined in series across an ac source $\displaystyle \mathrm{v}=140 \sin (100 \pi) \mathrm{tV}$. Find the rms voltages across these three circuit elements. The algebraic sum of these voltages is more than the rms voltage of source. Explain.(i)Write the principle of working of a transformer. With the help of a labelled diagram, explain the working of a step-up transformer.(ii)An ideal transformer is designed to convert $\displaystyle 50$ V into $\displaystyle 250$ V. It draws $\displaystyle 200$ W power from an ac source whose instantaneous voltage is given by $\displaystyle \mathrm{v}_{\mathrm{i}}=20 \sin (100 \pi) \mathrm{tV}$. Find:(I)$$ rms value of input current.(II)expression for instantaneous output voltage.(III)expression for instantaneous output current.
(i)
Write the principle of working of an ac generator. Draw its labelled diagram and explain its working.
(ii)
A resistor of $\displaystyle 400 \Omega$, an inductor of $\displaystyle \left(\frac{5}{\pi}\right) \mathrm{H}$ and a capacitor of $\displaystyle \left(\frac{50}{\pi}\right) \mu \mathrm{F}$ are joined in series across an ac source $\displaystyle \mathrm{v}=140 \sin (100 \pi) \mathrm{tV}$. Find the rms voltages across these three circuit elements. The algebraic sum of these voltages is more than the rms voltage of source. Explain.
(i)
Write the principle of working of a transformer. With the help of a labelled diagram, explain the working of a step-up transformer.
(ii)
An ideal transformer is designed to convert $\displaystyle 50$ V into $\displaystyle 250$ V. It draws $\displaystyle 200$ W power from an ac source whose instantaneous voltage is given by $\displaystyle \mathrm{v}_{\mathrm{i}}=20 \sin (100 \pi) \mathrm{tV}$. Find:
(I)
$$ rms value of input current.
(II)
expression for instantaneous output voltage.
(III)
expression for instantaneous output current.
Marking-scheme solution
(a)
(i) Principle: It works on the principle of electromagnetic induction.
Working: The coil is mechanically rotated in the uniform magnetic field. The rotation of the coil causes the magnetic flux through it to change, so an emf is induced in the coil.
(i) \(\displaystyle Z=\sqrt{R^{2}+\left(\omega L-\frac{1}{\omega C}\right)^{2}}\)
Alternating CurrentAC Voltage Applied to a Series LCR CircuitApplylong_answerhard
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CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.