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Physics · 2026 · 3 marks
CBSE 2026 · Region 3 · Set 2 · Q25
A series combination of circuit elements X and Y is connected across an ac source. It is found that the voltage is ahead of current in phase by (π)/4…
A series combination of circuit elements X and Y is connected across an ac source. It is found that the voltage is ahead of current in phase by $\displaystyle \frac{\pi}{4}$ radian. When element Y is replaced by element Z , the current leads the voltage by $\displaystyle \frac{\pi}{4}$ radian.
(a)
Identify the elements X, Y and Z.
(b)
What will the phase angle and power factor for the circuit be if X, Y and Z were connected in series across the same ac source ? What can you say about the current that flows in the circuit in this case ?
Marking-scheme solution
(a)
X – Resistor
Y – Inductor
Z – Capacitor
(b)
$\displaystyle \tan \dfrac{\pi}{4}=\dfrac{X_{L}}{R}$, so $\displaystyle X_{L}=R$
$\displaystyle \tan \dfrac{\pi}{4}=\dfrac{X_{C}}{R}$, so $\displaystyle X_{C}=R$
Phase angle: $\displaystyle \tan \phi=\dfrac{X_{L}-X_{C}}{R}=0$, so $\displaystyle \phi=0^{\circ}$
Power factor $\displaystyle =\cos \phi=\cos 0^{\circ}=1$
Current in the circuit is maximum.
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CBSE Class 12 Physics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.